Make QQuickAttachedPropertyPropagator public

This type has been used internally as QQuickAttachedObject by the
Imagine, Material and Universal styles to enable propagation of colors,
dark mode flags, etc. for a while now. Users would benefit from having
access to it to create their own styles (although it's not just limited
to that use case).

This patch:

- Makes the type public in quickcontrols2.
- Adds documentation and an example.
- Fixes the test_window test to ensure that propagation through child
  windows actually works.

[ChangeLog][Controls] Added QQuickAttachedPropertyPropagator, which
provides a way to propagate attached properties from parent objects
to children. This is especially useful when creating your own style.

Fixes: QTBUG-63267
Change-Id: I2f1794dc4a9f2be56fad2f5e5f39e2ab845157fa
Reviewed-by: Fabian Kosmale <[email protected]>
Reviewed-by: Richard Moe Gustavsen <[email protected]>

31 files changed, 1305 insertions, 363 deletions

diff --git a/examples/quickcontrols2/CMakeLists.txt b/examples/quickcontrols2/CMakeLists.txt
index 3473052f68..e4021bf430 100644
--- a/examples/quickcontrols2/CMakeLists.txt
+++ b/examples/quickcontrols2/CMakeLists.txt
@@ -1,6 +1,7 @@
 # Copyright (C) 2022 The Qt Company Ltd.
 # SPDX-License-Identifier: BSD-3-Clause
 
+qt_internal_add_example(attachedstyleproperties)
 qt_internal_add_example(gallery)
 if (TARGET Qt::Sql)
     add_subdirectory(chattutorial)
diff --git a/examples/quickcontrols2/attachedstyleproperties/CMakeLists.txt b/examples/quickcontrols2/attachedstyleproperties/CMakeLists.txt
new file mode 100644
index 0000000000..229129f5c6
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/CMakeLists.txt
@@ -0,0 +1,52 @@
+cmake_minimum_required(VERSION 3.16)
+project(attachedstyleproperties LANGUAGES CXX)
+
+set(CMAKE_AUTOMOC ON)
+
+if(NOT DEFINED INSTALL_EXAMPLESDIR)
+    set(INSTALL_EXAMPLESDIR "examples")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/quickcontrols2/attachedstyleproperties")
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Qml QuickControls2)
+qt_standard_project_setup()
+
+add_subdirectory(MyStyle)
+
+qt_add_executable(attachedstylepropertiesexample
+    WIN32
+    MACOSX_BUNDLE
+    attachedstyleproperties.cpp
+)
+
+qt_add_qml_module(attachedstylepropertiesexample
+    URI App
+    VERSION 1.0
+    QML_FILES
+        attachedstyleproperties.qml
+    NO_RESOURCE_TARGET_PATH
+)
+
+target_link_libraries(attachedstylepropertiesexample PRIVATE
+    Qt::Core
+    Qt::Gui
+    Qt::Qml
+    Qt::QuickControls2
+)
+
+add_dependencies(attachedstylepropertiesexample MyStyle)
+
+install(TARGETS attachedstylepropertiesexample
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)
+
+include(../../quick/shared/QtBundleQmlModuleForMacOS.cmake)
+
+set(app_target "attachedstylepropertiesexample")
+set(qml_plugin_target "MyStyleplugin")
+set(qml_module_uri "MyStyle")
+add_qml_module_to_macos_app_bundle(
+    "${app_target}" "${qml_plugin_target}" "${qml_module_uri}")
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/ApplicationWindow.qml b/examples/quickcontrols2/attachedstyleproperties/MyStyle/ApplicationWindow.qml
new file mode 100644
index 0000000000..8a7bbc7ed2
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/ApplicationWindow.qml
@@ -0,0 +1,17 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Templates as T
+
+import MyStyle
+
+T.ApplicationWindow {
+    color: MyStyle.windowColor
+
+    Behavior on color {
+        ColorAnimation {
+            duration: 150
+        }
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/Button.qml b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Button.qml
new file mode 100644
index 0000000000..7eabcb0b35
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Button.qml
@@ -0,0 +1,33 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Templates as T
+
+import MyStyle
+
+T.Button {
+    id: control
+
+    implicitWidth: Math.max(implicitBackgroundWidth + leftInset + rightInset,
+                            implicitContentWidth + leftPadding + rightPadding)
+    implicitHeight: Math.max(implicitBackgroundHeight + topInset + bottomInset,
+                             implicitContentHeight + topPadding + bottomPadding)
+
+    padding: 6
+    horizontalPadding: padding + 2
+    spacing: 6
+
+    contentItem: Text {
+        text: control.text
+        font: control.font
+        color: control.MyStyle.buttonTextColor
+        verticalAlignment: Text.AlignVCenter
+    }
+
+    background: Rectangle {
+        implicitWidth: 60
+        implicitHeight: 40
+        color: control.down ? Qt.darker(control.MyStyle.buttonColor, 1.1) : control.MyStyle.buttonColor
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/CMakeLists.txt b/examples/quickcontrols2/attachedstyleproperties/MyStyle/CMakeLists.txt
new file mode 100644
index 0000000000..310670677e
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/CMakeLists.txt
@@ -0,0 +1,47 @@
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+    message(FATAL_ERROR "MyStyle should be built as part of the 'attachedstyleproperties' project, and not in isolation.")
+endif()
+
+set(INSTALL_EXAMPLEDIR "${INSTALL_EXAMPLESDIR}/quickcontrols2/attachedstyleproperties")
+
+qt_add_qml_module(MyStyle
+    URI MyStyle
+    VERSION 1.0
+    IMPORTS
+        QtQuick.Controls.Material
+    QML_FILES
+        ApplicationWindow.qml
+        Button.qml
+        Label.qml
+        Popup.qml
+        Switch.qml
+        ToolBar.qml
+    SOURCES
+        mystyle.cpp
+        mystyle.h
+)
+
+include(GenerateExportHeader)
+target_include_directories(MyStyle PRIVATE ${CMAKE_CURRENT_BINARY_DIR}) # find autogenerated header
+generate_export_header(MyStyle)
+
+find_package(Qt6 REQUIRED COMPONENTS Core Gui Qml QuickControls2)
+
+target_link_libraries(MyStyle PRIVATE
+    Qt::Core
+    Qt::Gui
+    Qt::Qml
+    Qt::QuickControls2
+)
+
+message(STATUS "@@@ INSTALL_EXAMPLEDIR ${INSTALL_EXAMPLEDIR}")
+
+install(TARGETS MyStyle
+    RUNTIME DESTINATION "${INSTALL_EXAMPLEDIR}"
+    BUNDLE DESTINATION "${INSTALL_EXAMPLEDIR}"
+    LIBRARY DESTINATION "${INSTALL_EXAMPLEDIR}"
+)
+
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/qmldir
+    DESTINATION "${INSTALL_EXAMPLEDIR}"
+)
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/Label.qml b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Label.qml
new file mode 100644
index 0000000000..3d045aa70e
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Label.qml
@@ -0,0 +1,11 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Templates as T
+
+import MyStyle
+
+T.Label {
+    color: MyStyle.windowTextColor
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/Popup.qml b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Popup.qml
new file mode 100644
index 0000000000..0f5e753f60
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Popup.qml
@@ -0,0 +1,48 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Templates as T
+import MyStyle
+
+T.Popup {
+    id: control
+
+    implicitWidth: Math.max(implicitBackgroundWidth + leftInset + rightInset,
+                            contentWidth + leftPadding + rightPadding)
+    implicitHeight: Math.max(implicitBackgroundHeight + topInset + bottomInset,
+                             contentHeight + topPadding + bottomPadding)
+
+    padding: 12
+
+    enter: Transition {
+        NumberAnimation {
+            property: "opacity"
+            from: 0.0
+            to: 1.0
+            easing.type: Easing.OutCubic
+            duration: 150
+        }
+    }
+
+    exit: Transition {
+        NumberAnimation {
+            property: "opacity"
+            from: 1.0
+            to: 0.0
+            easing.type: Easing.OutCubic
+            duration: 150
+        }
+    }
+
+    background: Rectangle {
+        radius: 2
+        color: control.MyStyle.popupColor
+        border.color: control.MyStyle.popupBorderColor
+    }
+
+    T.Overlay.modeless: Rectangle {
+        color: control.MyStyle.backgroundDimColor
+        Behavior on opacity { NumberAnimation { duration: 150 } }
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/Switch.qml b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Switch.qml
new file mode 100644
index 0000000000..59bda147b7
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/Switch.qml
@@ -0,0 +1,58 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Templates as T
+
+import MyStyle
+
+T.Switch {
+    id: control
+
+    implicitWidth: Math.max(implicitBackgroundWidth + leftInset + rightInset,
+                            implicitContentWidth + leftPadding + rightPadding)
+    implicitHeight: Math.max(implicitBackgroundHeight + topInset + bottomInset,
+                             implicitContentHeight + topPadding + bottomPadding)
+
+    padding: 6
+    horizontalPadding: padding + 2
+    spacing: 6
+
+    indicator: Rectangle {
+        implicitWidth: 56
+        implicitHeight: 28
+
+        x: control.text
+           ? (control.mirrored ? control.width - width - control.rightPadding : control.leftPadding)
+           : control.leftPadding + (control.availableWidth - width) / 2
+        y: control.topPadding + (control.availableHeight - height) / 2
+
+        radius: 8
+        color: control.down ? Qt.darker(control.MyStyle.buttonColor, 1.1) : control.MyStyle.buttonColor
+
+        Rectangle {
+            x: Math.max(0, Math.min(parent.width - width, control.visualPosition * parent.width - (width / 2)))
+            y: (parent.height - height) / 2
+            width: 28
+            height: 28
+            radius: 8
+            color: Qt.lighter(control.MyStyle.buttonColor)
+
+            Behavior on x {
+                enabled: !control.down
+                SmoothedAnimation { velocity: 200 }
+            }
+        }
+    }
+
+    contentItem: Text {
+        leftPadding: control.indicator && !control.mirrored ? control.indicator.width + control.spacing : 0
+        rightPadding: control.indicator && control.mirrored ? control.indicator.width + control.spacing : 0
+
+        text: control.text
+        font: control.font
+        color: control.MyStyle.windowTextColor
+        elide: Text.ElideRight
+        verticalAlignment: Text.AlignVCenter
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/ToolBar.qml b/examples/quickcontrols2/attachedstyleproperties/MyStyle/ToolBar.qml
new file mode 100644
index 0000000000..b0cd597c87
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/ToolBar.qml
@@ -0,0 +1,24 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Templates as T
+
+import MyStyle
+
+T.ToolBar {
+    id: control
+
+    implicitWidth: Math.max(implicitBackgroundWidth + leftInset + rightInset,
+                            contentWidth + leftPadding + rightPadding)
+    implicitHeight: Math.max(implicitBackgroundHeight + topInset + bottomInset,
+                             contentHeight + topPadding + bottomPadding)
+
+    background: Rectangle {
+        implicitHeight: 40
+        // Ensure that we use Control's attached MyStyle object by qualifying
+        // the binding with its id. If we don't do this, an extra, unnecessary
+        // attached MyStyle object will be created for the Rectangle.
+        color: control.MyStyle.toolBarColor
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp b/examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
new file mode 100644
index 0000000000..40f7af702e
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
@@ -0,0 +1,136 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include "mystyle.h"
+
+// If no value was inherited from a parent or explicitly set, the "global" values are used.
+static MyStyle::Theme globalTheme = MyStyle::Light;
+
+MyStyle::MyStyle(QObject *parent)
+    : QQuickAttachedPropertyPropagator(parent)
+    , m_theme(globalTheme)
+{
+    // A static function could be called here that reads globalTheme from a
+    // settings file once at startup. That value would override the global
+    // value. This is similar to what the Imagine and Material styles do, for
+    // example.
+
+    initialize();
+}
+
+MyStyle *MyStyle::qmlAttachedProperties(QObject *object)
+{
+    return new MyStyle(object);
+}
+
+MyStyle::Theme MyStyle::theme() const
+{
+    return m_theme;
+}
+
+void MyStyle::setTheme(Theme theme)
+{
+    // When this function is called, we know that the user has explicitly
+    // set a theme on this attached object. We set this to true even if
+    // the effective theme didn't change, because it's important that
+    // the user's specified value is respected (and not inherited from
+    // from the parent).
+    m_explicitTheme = true;
+    if (m_theme == theme)
+        return;
+
+    m_theme = theme;
+    propagateTheme();
+    themeChange();
+
+}
+
+void MyStyle::inheritTheme(Theme theme)
+{
+    if (m_explicitTheme || m_theme == theme)
+        return;
+
+    m_theme = theme;
+    propagateTheme();
+    themeChange();
+}
+
+void MyStyle::propagateTheme()
+{
+    const auto styles = attachedChildren();
+    for (QQuickAttachedPropertyPropagator *child : styles) {
+        MyStyle *myStyle = qobject_cast<MyStyle *>(child);
+        if (myStyle)
+            myStyle->inheritTheme(m_theme);
+    }
+}
+
+void MyStyle::resetTheme()
+{
+    if (!m_explicitTheme)
+        return;
+
+    m_explicitTheme = false;
+    MyStyle *myStyle = qobject_cast<MyStyle *>(attachedParent());
+    inheritTheme(myStyle ? myStyle->theme() : globalTheme);
+}
+
+void MyStyle::themeChange()
+{
+    emit themeChanged();
+    // Emit any other change signals for properties that depend on the theme here...
+}
+
+QColor MyStyle::windowColor() const
+{
+    return m_theme == Light ? QColor::fromRgb(0xf0f0f0) : QColor::fromRgb(0x303030);
+}
+
+QColor MyStyle::windowTextColor() const
+{
+    return m_theme == Light ? QColor::fromRgb(0x5c5c5c) : QColor::fromRgb(0xe0e0e0);
+}
+
+QColor MyStyle::buttonColor() const
+{
+    return m_theme == Light ? QColor::fromRgb(0xc2e1ff) : QColor::fromRgb(0x74bbff);
+}
+
+QColor MyStyle::buttonTextColor() const
+{
+    return m_theme == Light ? QColor::fromRgb(0x5c5c5c) : QColor::fromRgb(0xffffff);
+}
+
+QColor MyStyle::toolBarColor() const
+{
+    return m_theme == Light ? QColor::fromRgb(0x4da6ff) : QColor::fromRgb(0x0066cc);
+}
+
+QColor MyStyle::popupColor() const
+{
+//    const QColor winColor = windowColor();
+//    return m_theme == Light ? winColor.darker(120) : winColor.lighter(120);
+    return windowColor().lighter(120);
+}
+
+QColor MyStyle::popupBorderColor() const
+{
+    const QColor winColor = windowColor();
+    return m_theme == Light ? winColor.darker(140) : winColor.lighter(140);
+}
+
+QColor MyStyle::backgroundDimColor() const
+{
+    const QColor winColor = windowColor().darker();
+    return QColor::fromRgb(winColor.red(), winColor.green(), winColor.blue(), 100);
+}
+
+void MyStyle::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)
+{
+    Q_UNUSED(oldParent);
+    MyStyle *attachedParentStyle = qobject_cast<MyStyle *>(newParent);
+    if (attachedParentStyle) {
+        inheritTheme(attachedParentStyle->theme());
+        // Do any other inheriting here...
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.h b/examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.h
new file mode 100644
index 0000000000..da87ab4718
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.h
@@ -0,0 +1,76 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#ifndef MYSTYLE_H
+#define MYSTYLE_H
+
+#include <QColor>
+#include <QQmlEngine>
+#include <QQuickAttachedPropertyPropagator>
+
+#include "mystyle_export.h"
+
+class MYSTYLE_EXPORT MyStyle : public QQuickAttachedPropertyPropagator
+{
+    Q_OBJECT
+    // Provide a RESET function in order to allow an item to set MyStyle.theme to undefined
+    // in order to use its parent's (or global) theme after one was explicitly set on it.
+    Q_PROPERTY(Theme theme READ theme WRITE setTheme RESET resetTheme NOTIFY themeChanged FINAL)
+    // As the values of these properties only depend on the theme, they can all use the theme
+    // property's change signal.
+    Q_PROPERTY(QColor windowColor READ windowColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor windowTextColor READ windowTextColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor buttonColor READ buttonColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor buttonTextColor READ buttonTextColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor toolBarColor READ toolBarColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor popupColor READ popupColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor popupBorderColor READ popupBorderColor NOTIFY themeChanged FINAL)
+    Q_PROPERTY(QColor backgroundDimColor READ backgroundDimColor NOTIFY themeChanged FINAL)
+
+    QML_ELEMENT
+    QML_ATTACHED(MyStyle)
+    QML_UNCREATABLE("")
+    QML_ADDED_IN_VERSION(1, 0)
+
+public:
+    enum Theme {
+        Light,
+        Dark
+    };
+
+    Q_ENUM(Theme)
+
+    explicit MyStyle(QObject *parent = nullptr);
+
+    static MyStyle *qmlAttachedProperties(QObject *object);
+
+    Theme theme() const;
+    void setTheme(Theme theme);
+    void inheritTheme(Theme theme);
+    void propagateTheme();
+    void resetTheme();
+    void themeChange();
+
+    QColor windowColor() const;
+    QColor windowTextColor() const;
+    QColor buttonColor() const;
+    QColor buttonTextColor() const;
+    QColor toolBarColor() const;
+    QColor popupColor() const;
+    QColor popupBorderColor() const;
+    QColor backgroundDimColor() const;
+
+Q_SIGNALS:
+    void themeChanged();
+
+protected:
+    void attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent) override;
+
+private:
+    // Whether a color value was explicitly set on the specific object that this attached style object represents.
+    bool m_explicitTheme = false;
+    // The actual values for this item, whether explicit, inherited or globally set.
+    Theme m_theme = Light;
+};
+
+#endif // MYSTYLE_H
diff --git a/examples/quickcontrols2/attachedstyleproperties/attachedstyleproperties.cpp b/examples/quickcontrols2/attachedstyleproperties/attachedstyleproperties.cpp
new file mode 100644
index 0000000000..376e53c055
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/attachedstyleproperties.cpp
@@ -0,0 +1,28 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+#include <QGuiApplication>
+#include <QQmlApplicationEngine>
+#include <QDir>
+
+int main(int argc, char *argv[])
+{
+    QGuiApplication app(argc, argv);
+    app.setOrganizationName("QtProject");
+    app.setOrganizationDomain("qt-project.org");
+    app.setApplicationName("Attached Objects");
+
+    QQmlApplicationEngine engine;
+#ifdef Q_OS_MACOS
+    engine.addImportPath(app.applicationDirPath() + "/../PlugIns");
+#endif
+    const QUrl url(QStringLiteral("qrc:/attachedstyleproperties.qml"));
+    QObject::connect(&engine, &QQmlApplicationEngine::objectCreated,
+                     &app, [url](QObject *obj, const QUrl &objUrl) {
+        if (!obj && url == objUrl)
+            QCoreApplication::exit(-1);
+    }, Qt::QueuedConnection);
+    engine.load(url);
+
+    return app.exec();
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/attachedstyleproperties.qml b/examples/quickcontrols2/attachedstyleproperties/attachedstyleproperties.qml
new file mode 100644
index 0000000000..e08e19801f
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/attachedstyleproperties.qml
@@ -0,0 +1,110 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR BSD-3-Clause
+
+import QtQuick
+import QtQuick.Layouts
+
+import MyStyle
+
+ApplicationWindow {
+    width: 800
+    height: 600
+    title: qsTr("Attached Objects")
+    visible: true
+
+    MyStyle.theme: darkModeSwitch.checked ? MyStyle.Dark : MyStyle.Light
+
+    header: ToolBar {
+        MyStyle.theme: MyStyle.Dark
+
+        RowLayout {
+            anchors.fill: parent
+            anchors.leftMargin: 12
+
+            Label {
+                text: qsTr("This is a Label in a ToolBar")
+            }
+
+            Item {
+                Layout.fillWidth: true
+            }
+
+            Switch {
+                id: darkModeSwitch
+                text: qsTr("Dark mode")
+            }
+        }
+    }
+
+    ColumnLayout {
+        anchors.centerIn: parent
+        spacing: 20
+
+        Label {
+            text: qsTr("This is a Label in an ApplicationWindow")
+            Layout.alignment: Qt.AlignHCenter
+        }
+
+        RowLayout {
+            Button {
+                text: qsTr("Open Popup")
+                onClicked: popup.open()
+            }
+
+            Button {
+                text: qsTr("Open Window")
+                onClicked: {
+                    if (!childWindow.active)
+                        childWindow.show()
+                    else
+                        childWindow.raise()
+                }
+            }
+        }
+    }
+
+    Popup {
+        id: popup
+        dim: true
+        anchors.centerIn: parent
+
+        ColumnLayout {
+            anchors.centerIn: parent
+            spacing: 20
+
+            Label {
+                text: qsTr("This is a Label in a Popup")
+                Layout.alignment: Qt.AlignHCenter
+            }
+
+            Button {
+                text: qsTr("Close Popup")
+                Layout.alignment: Qt.AlignHCenter
+                onClicked: popup.close()
+            }
+        }
+    }
+
+    ApplicationWindow {
+        id: childWindow
+        width: 600
+        height: 400
+        title: qsTr("Attached Objects - Child Window")
+
+        ColumnLayout {
+            anchors.centerIn: parent
+            spacing: 20
+
+            Label {
+                text: qsTr("This is a Label in a child ApplicationWindow")
+                Layout.alignment: Qt.AlignHCenter
+            }
+
+            Button {
+                text: qsTr("Close Window")
+                Layout.alignment: Qt.AlignHCenter
+                onClicked: childWindow.close()
+            }
+        }
+    }
+}
diff --git a/examples/quickcontrols2/attachedstyleproperties/doc/images/qtquickcontrols2-attachedstyleproperties.png b/examples/quickcontrols2/attachedstyleproperties/doc/images/qtquickcontrols2-attachedstyleproperties.png
new file mode 100644
index 0000000000..2cd5f214f7
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/doc/images/qtquickcontrols2-attachedstyleproperties.png
diff --git a/examples/quickcontrols2/attachedstyleproperties/doc/src/qtquickcontrols2-attachedstyleproperties.qdoc b/examples/quickcontrols2/attachedstyleproperties/doc/src/qtquickcontrols2-attachedstyleproperties.qdoc
new file mode 100644
index 0000000000..de43fc80bd
--- /dev/null
+++ b/examples/quickcontrols2/attachedstyleproperties/doc/src/qtquickcontrols2-attachedstyleproperties.qdoc
@@ -0,0 +1,18 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR GFDL-1.3-no-invariants-only
+
+/*!
+    \example attachedstyleproperties
+    \keyword Qt Quick Controls - Attached Style Properties Example
+    \title Qt Quick Controls - Attached Style Properties Example
+    \ingroup qtquickcontrols2-examples
+    \brief Demonstrates use of QQuickAttachedPropertyPropagator.
+
+    \image qtquickcontrols2-attachedstyleproperties.png
+
+    The Attached Style Properties example is a simple application that shows
+    how to use \l QQuickAttachedPropertyPropagator to propagate attached
+    property values to child objects.
+
+    \include examples-run.qdocinc
+*/
diff --git a/src/qml/doc/src/cppintegration/definetypes.qdoc b/src/qml/doc/src/cppintegration/definetypes.qdoc
index 5799fda87e..e6a6dbfe36 100644
--- a/src/qml/doc/src/cppintegration/definetypes.qdoc
+++ b/src/qml/doc/src/cppintegration/definetypes.qdoc
@@ -595,6 +595,14 @@ qDebug() << "Value of MessageBoard.expired:" << attached->expired();
 \endcode
 
 
+\section3 Propagating Attached Properties
+
+\l QQuickAttachedPropertyPropagator can be subclassed to propagate attached properties
+from a parent object to its children, similar to \l {Control::}{font} and
+\l {Item::}{palette} propagation. It supports propagation through
+\l {Item}{items}, \l {Popup}{popups}, and \l {Window}{windows}.
+
+
 \section2 Property Modifier Types
 
 A property modifier type is a special kind of QML object type.  A property
diff --git a/src/quickcontrols2/CMakeLists.txt b/src/quickcontrols2/CMakeLists.txt
index 65dbf409b3..24a2ca8ca2 100644
--- a/src/quickcontrols2/CMakeLists.txt
+++ b/src/quickcontrols2/CMakeLists.txt
@@ -27,6 +27,7 @@ qt_internal_add_qml_module(QuickControls2
     NO_PLUGIN_OPTIONAL
     NO_GENERATE_PLUGIN_SOURCE
     SOURCES
+        qquickattachedpropertypropagator.cpp qquickattachedpropertypropagator.h
         qquickstyle.cpp qquickstyle.h qquickstyle_p.h
         qquickstyleplugin.cpp qquickstyleplugin_p.h
         qtquickcontrols2global.h
diff --git a/src/quickcontrols2/imagine/qquickimaginestyle.cpp b/src/quickcontrols2/imagine/qquickimaginestyle.cpp
index e3270cec49..377103e2f2 100644
--- a/src/quickcontrols2/imagine/qquickimaginestyle.cpp
+++ b/src/quickcontrols2/imagine/qquickimaginestyle.cpp
@@ -17,7 +17,7 @@ static QString ensureSlash(const QString &path)
 }
 
 QQuickImagineStyle::QQuickImagineStyle(QObject *parent)
-    : QQuickAttachedObject(parent),
+    : QQuickAttachedPropertyPropagator(parent),
       m_path(*GlobalPath())
 {
     init();
@@ -58,7 +58,7 @@ void QQuickImagineStyle::inheritPath(const QString &path)
 void QQuickImagineStyle::propagatePath()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickImagineStyle *imagine = qobject_cast<QQuickImagineStyle *>(child);
         if (imagine)
             imagine->inheritPath(m_path);
@@ -98,7 +98,7 @@ QUrl QQuickImagineStyle::url() const
     return QUrl::fromLocalFile(path);
 }
 
-void QQuickImagineStyle::attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent)
+void QQuickImagineStyle::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)
 {
     Q_UNUSED(oldParent);
     QQuickImagineStyle *imagine = qobject_cast<QQuickImagineStyle *>(newParent);
@@ -129,7 +129,7 @@ void QQuickImagineStyle::init()
         globalsInitialized = true;
     }
 
-    QQuickAttachedObject::init(); // TODO: lazy init?
+    QQuickAttachedPropertyPropagator::initialize(); // TODO: lazy init?
 }
 
 QT_END_NAMESPACE
diff --git a/src/quickcontrols2/imagine/qquickimaginestyle_p.h b/src/quickcontrols2/imagine/qquickimaginestyle_p.h
index 738577080f..81f17fb58c 100644
--- a/src/quickcontrols2/imagine/qquickimaginestyle_p.h
+++ b/src/quickcontrols2/imagine/qquickimaginestyle_p.h
@@ -17,11 +17,11 @@
 
 #include <QtCore/qvariant.h>
 #include <QtQml/qqml.h>
-#include <QtQuickControls2Impl/private/qquickattachedobject_p.h>
+#include <QtQuickControls2/qquickattachedpropertypropagator.h>
 
 QT_BEGIN_NAMESPACE
 
-class QQuickImagineStyle : public QQuickAttachedObject
+class QQuickImagineStyle : public QQuickAttachedPropertyPropagator
 {
     Q_OBJECT
     Q_PROPERTY(QString path READ path WRITE setPath RESET resetPath NOTIFY pathChanged FINAL)
@@ -48,7 +48,7 @@ Q_SIGNALS:
     void pathChanged();
 
 protected:
-    void attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent) override;
+    void attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent) override;
 
 private:
     void init();
diff --git a/src/quickcontrols2/ios/qquickiosstyle.cpp b/src/quickcontrols2/ios/qquickiosstyle.cpp
index f773833f00..74338d370c 100644
--- a/src/quickcontrols2/ios/qquickiosstyle.cpp
+++ b/src/quickcontrols2/ios/qquickiosstyle.cpp
@@ -18,7 +18,7 @@ static QQuickIOSStyle::Theme qquickios_effective_theme()
 }
 
 QQuickIOSStyle::QQuickIOSStyle(QObject *parent)
-    : QQuickAttachedObject(parent)
+    : QQuickAttachedPropertyPropagator(parent)
 {
     init();
     m_theme = qquickios_effective_theme();
@@ -41,7 +41,7 @@ void QQuickIOSStyle::init()
     //     QSharedPointer<QSettings> settings = QQuickStylePrivate::settings(QStringLiteral("iOS"));
     //     globalsInitialized = true;
     // }
-    QQuickAttachedObject::init(); // TODO: lazy init?
+    QQuickAttachedPropertyPropagator::initialize(); // TODO: lazy init?
 }
 
 QQuickIOSStyle::Theme QQuickIOSStyle::theme() const
diff --git a/src/quickcontrols2/ios/qquickiosstyle_p.h b/src/quickcontrols2/ios/qquickiosstyle_p.h
index 49e5dde0a1..b71d9b0f86 100644
--- a/src/quickcontrols2/ios/qquickiosstyle_p.h
+++ b/src/quickcontrols2/ios/qquickiosstyle_p.h
@@ -17,11 +17,11 @@
 
 #include <QtCore/qvariant.h>
 #include <QtQml/qqml.h>
-#include <QtQuickControls2Impl/private/qquickattachedobject_p.h>
+#include <QtQuickControls2/qquickattachedpropertypropagator.h>
 
 QT_BEGIN_NAMESPACE
 
-class QQuickIOSStyle : public QQuickAttachedObject
+class QQuickIOSStyle : public QQuickAttachedPropertyPropagator
 {
     Q_OBJECT
     Q_PROPERTY(QUrl url READ url CONSTANT)
diff --git a/src/quickcontrols2/material/qquickmaterialstyle.cpp b/src/quickcontrols2/material/qquickmaterialstyle.cpp
index b4c782f023..9114462828 100644
--- a/src/quickcontrols2/material/qquickmaterialstyle.cpp
+++ b/src/quickcontrols2/material/qquickmaterialstyle.cpp
@@ -399,7 +399,7 @@ static QQuickMaterialStyle::Theme effectiveTheme(QQuickMaterialStyle::Theme them
     return theme;
 }
 
-QQuickMaterialStyle::QQuickMaterialStyle(QObject *parent) : QQuickAttachedObject(parent),
+QQuickMaterialStyle::QQuickMaterialStyle(QObject *parent) : QQuickAttachedPropertyPropagator(parent),
     m_customPrimary(globalPrimaryCustom),
     m_customAccent(globalAccentCustom),
     m_customForeground(globalForegroundCustom),
@@ -412,7 +412,7 @@ QQuickMaterialStyle::QQuickMaterialStyle(QObject *parent) : QQuickAttachedObject
     m_foreground(globalForeground),
     m_background(globalBackground)
 {
-    QQuickAttachedObject::init();
+    QQuickAttachedPropertyPropagator::initialize();
 }
 
 QQuickMaterialStyle *QQuickMaterialStyle::qmlAttachedProperties(QObject *object)
@@ -464,7 +464,7 @@ void QQuickMaterialStyle::inheritTheme(Theme theme)
 void QQuickMaterialStyle::propagateTheme()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickMaterialStyle *material = qobject_cast<QQuickMaterialStyle *>(child);
         if (material)
             material->inheritTheme(m_theme);
@@ -530,7 +530,7 @@ void QQuickMaterialStyle::inheritPrimary(uint primary, bool custom)
 void QQuickMaterialStyle::propagatePrimary()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickMaterialStyle *material = qobject_cast<QQuickMaterialStyle *>(child);
         if (material)
             material->inheritPrimary(m_primary, m_customPrimary);
@@ -594,7 +594,7 @@ void QQuickMaterialStyle::inheritAccent(uint accent, bool custom)
 void QQuickMaterialStyle::propagateAccent()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickMaterialStyle *material = qobject_cast<QQuickMaterialStyle *>(child);
         if (material)
             material->inheritAccent(m_accent, m_customAccent);
@@ -666,7 +666,7 @@ void QQuickMaterialStyle::inheritForeground(uint foreground, bool custom, bool h
 void QQuickMaterialStyle::propagateForeground()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickMaterialStyle *material = qobject_cast<QQuickMaterialStyle *>(child);
         if (material)
             material->inheritForeground(m_foreground, m_customForeground, m_hasForeground);
@@ -731,7 +731,7 @@ void QQuickMaterialStyle::inheritBackground(uint background, bool custom, bool h
 void QQuickMaterialStyle::propagateBackground()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickMaterialStyle *material = qobject_cast<QQuickMaterialStyle *>(child);
         if (material)
             material->inheritBackground(m_background, m_customBackground, m_hasBackground);
@@ -1319,7 +1319,7 @@ void QQuickMaterialStyle::initGlobals()
     }
 }
 
-void QQuickMaterialStyle::attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent)
+void QQuickMaterialStyle::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)
 {
     Q_UNUSED(oldParent);
     QQuickMaterialStyle *material = qobject_cast<QQuickMaterialStyle *>(newParent);
diff --git a/src/quickcontrols2/material/qquickmaterialstyle_p.h b/src/quickcontrols2/material/qquickmaterialstyle_p.h
index 5c009b124b..99344a6192 100644
--- a/src/quickcontrols2/material/qquickmaterialstyle_p.h
+++ b/src/quickcontrols2/material/qquickmaterialstyle_p.h
@@ -16,11 +16,12 @@
 //
 
 #include <QtGui/qcolor.h>
-#include <QtQuickControls2Impl/private/qquickattachedobject_p.h>
+#include <QtQml/qqml.h>
+#include <QtQuickControls2/qquickattachedpropertypropagator.h>
 
 QT_BEGIN_NAMESPACE
 
-class QQuickMaterialStyle : public QQuickAttachedObject
+class QQuickMaterialStyle : public QQuickAttachedPropertyPropagator
 {
     Q_OBJECT
     Q_PROPERTY(Theme theme READ theme WRITE setTheme RESET resetTheme NOTIFY themeChanged FINAL)
@@ -256,7 +257,7 @@ Q_SIGNALS:
     void toolTextColorChanged();
 
 protected:
-    void attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent) override;
+    void attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent) override;
 
 private:
     void init();
diff --git a/src/quickcontrols2/qquickattachedpropertypropagator.cpp b/src/quickcontrols2/qquickattachedpropertypropagator.cpp
new file mode 100644
index 0000000000..07bcb93d7f
--- /dev/null
+++ b/src/quickcontrols2/qquickattachedpropertypropagator.cpp
@@ -0,0 +1,380 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#include "qquickattachedpropertypropagator.h"
+
+#include <QtCore/qpointer.h>
+#include <QtQuick/qquickwindow.h>
+#include <QtQuick/private/qquickitem_p.h>
+#include <QtQuick/private/qquickitemchangelistener_p.h>
+#include <QtQuickTemplates2/private/qquickpopup_p.h>
+
+QT_BEGIN_NAMESPACE
+
+/*!
+    \class QQuickAttachedPropertyPropagator
+    \brief The QQuickAttachedPropertyPropagator class provides a way to
+    propagate attached properties.
+    \inmodule QtQuickControls2
+    \since 6.5
+
+    In QML, it is possible to
+    \l {Attached Properties and Attached Signal Handlers}{attach properties and
+    signal handlers} to objects. \l {Providing Attached Properties} goes into more
+    detail about how to expose your own C++ attached types.
+
+    QQuickAttachedPropertyPropagator provides an API to propagate attached
+    properties from a parent object to its children, similar to
+    \l {Control::}{font} and \l {Item::}{palette} propagation. It supports
+    propagation through \l {Item}{items}, \l {Popup}{popups}, and
+    \l {Window}{windows}.
+
+    If propagation of properties is not important, consider using a
+    \l {QML_SINGLETON}{C++} or
+    \l {Contents of a Module Definition qmldir File}{QML} singleton instead,
+    as it is better suited for that use case, and is more efficient in that
+    it only requires one QObject.
+
+    To use QQuickAttachedPropertyPropagator:
+    \list
+    \li Derive from it
+    \li Call \l initialize() in the constructor
+    \li Define set/inherit/propagate/reset functions for each property as needed
+    \li Reimplement \l attachedParentChange() to handle property inheritance
+    \endlist
+
+    For an example that demonstrates this in depth, see
+    \l {Qt Quick Controls - Attached Style Properties Example}.
+
+    \sa {Styling Qt Quick Controls}
+*/
+
+static QQuickAttachedPropertyPropagator *attachedObject(const QMetaObject *type, QObject *object, bool create = false)
+{
+    if (!object)
+        return nullptr;
+    auto func = qmlAttachedPropertiesFunction(object, type);
+    return qobject_cast<QQuickAttachedPropertyPropagator *>(qmlAttachedPropertiesObject(object, func, create));
+}
+
+/*!
+    \internal
+
+    Tries to find a QQuickAttachedPropertyPropagator whose type is \a ourAttachedType
+    and is attached to an ancestor of \a objectWeAreAttachedTo.
+
+    QQuickAttachedPropertyPropagator needs to know who its parent attached object is in
+    order to inherit attached property values from it. This is called when an
+    instance of QQuickAttachedPropertyPropagator is created, and whenever
+    \c {objectWeAreAttachedTo}'s parent changes, for example.
+*/
+static QQuickAttachedPropertyPropagator *findAttachedParent(const QMetaObject *ourAttachedType, QObject *objectWeAreAttachedTo)
+{
+    QQuickItem *item = qobject_cast<QQuickItem *>(objectWeAreAttachedTo);
+    if (item) {
+        // lookup parent items and popups
+        QQuickItem *parent = item->parentItem();
+        while (parent) {
+            QQuickAttachedPropertyPropagator *attached = attachedObject(ourAttachedType, parent);
+            if (attached)
+                return attached;
+
+            QQuickPopup *popup = qobject_cast<QQuickPopup *>(parent->parent());
+            if (popup)
+                return attachedObject(ourAttachedType, popup);
+
+            parent = parent->parentItem();
+        }
+
+        // fallback to item's window
+        QQuickAttachedPropertyPropagator *attached = attachedObject(ourAttachedType, item->window());
+        if (attached)
+            return attached;
+    } else {
+        // lookup popup's window
+        QQuickPopup *popup = qobject_cast<QQuickPopup *>(objectWeAreAttachedTo);
+        if (popup)
+            return attachedObject(ourAttachedType, popup->popupItem()->window());
+    }
+
+    // lookup parent window
+    QQuickWindow *window = qobject_cast<QQuickWindow *>(objectWeAreAttachedTo);
+    if (window) {
+        // It doesn't seem like a parent window can be anything but transient in Qt Quick.
+        QQuickWindow *parentWindow = qobject_cast<QQuickWindow *>(window->transientParent());
+        if (parentWindow) {
+            QQuickAttachedPropertyPropagator *attached = attachedObject(ourAttachedType, parentWindow);
+            if (attached)
+                return attached;
+        }
+    }
+
+    // fallback to engine (global)
+    if (objectWeAreAttachedTo) {
+        QQmlEngine *engine = qmlEngine(objectWeAreAttachedTo);
+        if (engine) {
+            QByteArray name = QByteArray("_q_") + ourAttachedType->className();
+            QQuickAttachedPropertyPropagator *attached = engine->property(name).value<QQuickAttachedPropertyPropagator *>();
+            if (!attached) {
+                attached = attachedObject(ourAttachedType, engine, true);
+                engine->setProperty(name, QVariant::fromValue(attached));
+            }
+            return attached;
+        }
+    }
+
+    return nullptr;
+}
+
+static QList<QQuickAttachedPropertyPropagator *> findAttachedChildren(const QMetaObject *type, QObject *object)
+{
+    QList<QQuickAttachedPropertyPropagator *> children;
+
+    QQuickItem *item = qobject_cast<QQuickItem *>(object);
+    if (!item) {
+        QQuickWindow *window = qobject_cast<QQuickWindow *>(object);
+        if (window)
+            item = window->contentItem();
+    }
+
+    if (!item)
+        return children;
+
+    // At this point, "item" could either be an item that the attached object is
+    // attached to directly, or the contentItem of a window that the attached object
+    // is attached to.
+
+    // Look for attached properties on items.
+    const auto childItems = item->childItems();
+    for (QQuickItem *child : childItems) {
+        QQuickAttachedPropertyPropagator *attached = attachedObject(type, child);
+        if (attached)
+            children += attached;
+        else
+            children += findAttachedChildren(type, child);
+    }
+
+    // Look for attached properties on windows. Windows declared in QML
+    // as children of a Window are QObject-parented to the contentItem (see
+    // QQuickWindowPrivate::data_append()). Windows declared as children
+    // of items are QObject-parented to those items.
+    const auto &windowChildren = item->children();
+    for (QObject *child : windowChildren) {
+        QQuickWindow *childWindow = qobject_cast<QQuickWindow *>(child);
+        if (childWindow) {
+            QQuickAttachedPropertyPropagator *attached = attachedObject(type, childWindow);
+            if (attached)
+                children += attached;
+        }
+    }
+
+    return children;
+}
+
+static QQuickItem *findAttachedItem(QObject *parent)
+{
+    QQuickItem *item = qobject_cast<QQuickItem *>(parent);
+    if (!item) {
+        QQuickPopup *popup = qobject_cast<QQuickPopup *>(parent);
+        if (popup)
+            item = popup->popupItem();
+    }
+    return item;
+}
+
+class QQuickAttachedPropertyPropagatorPrivate : public QObjectPrivate, public QQuickItemChangeListener
+{
+public:
+    Q_DECLARE_PUBLIC(QQuickAttachedPropertyPropagator)
+
+    static QQuickAttachedPropertyPropagatorPrivate *get(QQuickAttachedPropertyPropagator *attachedObject)
+    {
+        return attachedObject->d_func();
+    }
+
+    void attachTo(QObject *object);
+    void detachFrom(QObject *object);
+    void setAttachedParent(QQuickAttachedPropertyPropagator *parent);
+
+    void itemWindowChanged(QQuickWindow *window);
+    void itemParentChanged(QQuickItem *item, QQuickItem *parent) override;
+
+    QList<QQuickAttachedPropertyPropagator *> attachedChildren;
+    QPointer<QQuickAttachedPropertyPropagator> attachedParent;
+};
+
+void QQuickAttachedPropertyPropagatorPrivate::attachTo(QObject *object)
+{
+    QQuickItem *item = findAttachedItem(object);
+    if (item) {
+        connect(item, &QQuickItem::windowChanged, this, &QQuickAttachedPropertyPropagatorPrivate::itemWindowChanged);
+        QQuickItemPrivate::get(item)->addItemChangeListener(this, QQuickItemPrivate::Parent);
+    }
+}
+
+void QQuickAttachedPropertyPropagatorPrivate::detachFrom(QObject *object)
+{
+    QQuickItem *item = findAttachedItem(object);
+    if (item) {
+        disconnect(item, &QQuickItem::windowChanged, this, &QQuickAttachedPropertyPropagatorPrivate::itemWindowChanged);
+        QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::Parent);
+    }
+}
+
+/*!
+    \internal
+
+    This function sets the attached parent of this attached object.
+
+    Currently it is called when:
+    \list
+    \li The target item's parent changes.
+    \li The target item's window changes.
+    \li The attached object is constructed, to set the attached parent
+        and the attached parent of the attached object children.
+    \li The attached object is destructed.
+    \endlist
+
+    \quotefromfile ../../examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
+    \skipto MyStyle::resetTheme
+    \printuntil }
+*/
+void QQuickAttachedPropertyPropagatorPrivate::setAttachedParent(QQuickAttachedPropertyPropagator *parent)
+{
+    Q_Q(QQuickAttachedPropertyPropagator);
+    if (attachedParent == parent)
+        return;
+
+    QQuickAttachedPropertyPropagator *oldParent = attachedParent;
+    if (attachedParent)
+        QQuickAttachedPropertyPropagatorPrivate::get(attachedParent)->attachedChildren.removeOne(q);
+    attachedParent = parent;
+    if (parent)
+        QQuickAttachedPropertyPropagatorPrivate::get(parent)->attachedChildren.append(q);
+    q->attachedParentChange(parent, oldParent);
+}
+
+void QQuickAttachedPropertyPropagatorPrivate::itemWindowChanged(QQuickWindow *window)
+{
+    Q_Q(QQuickAttachedPropertyPropagator);
+    QQuickAttachedPropertyPropagator *attachedParent = nullptr;
+    QQuickItem *item = qobject_cast<QQuickItem *>(q->sender());
+    if (item)
+        attachedParent = findAttachedParent(q->metaObject(), item);
+    if (!attachedParent)
+        attachedParent = attachedObject(q->metaObject(), window);
+    setAttachedParent(attachedParent);
+}
+
+void QQuickAttachedPropertyPropagatorPrivate::itemParentChanged(QQuickItem *item, QQuickItem *parent)
+{
+    Q_Q(QQuickAttachedPropertyPropagator);
+    Q_UNUSED(parent);
+    setAttachedParent(findAttachedParent(q->metaObject(), item));
+}
+
+/*!
+    Constructs a QQuickAttachedPropertyPropagator with the given \a parent.
+
+    The \c parent will be used to find this object's
+    \l {attachedParent()}{attached parent}.
+
+    Derived classes should call \l initialize() in their constructor.
+*/
+QQuickAttachedPropertyPropagator::QQuickAttachedPropertyPropagator(QObject *parent)
+    : QObject(*(new QQuickAttachedPropertyPropagatorPrivate), parent)
+{
+    Q_D(QQuickAttachedPropertyPropagator);
+    d->attachTo(parent);
+}
+
+/*!
+    Destroys the QQuickAttachedPropertyPropagator.
+*/
+QQuickAttachedPropertyPropagator::~QQuickAttachedPropertyPropagator()
+{
+    Q_D(QQuickAttachedPropertyPropagator);
+    d->detachFrom(parent());
+    d->setAttachedParent(nullptr);
+}
+
+/*!
+    This function returns the attached children of this attached object.
+
+    The attached children are used when propagating property values:
+
+    \quotefromfile ../../examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
+    \skipto MyStyle::propagateTheme
+    \printuntil }
+    \printuntil }
+*/
+QList<QQuickAttachedPropertyPropagator *> QQuickAttachedPropertyPropagator::attachedChildren() const
+{
+    Q_D(const QQuickAttachedPropertyPropagator);
+    return d->attachedChildren;
+}
+
+/*!
+    This function returns the attached parent of this attached object.
+
+    The attached parent is used when inheriting property values:
+
+    \quotefromfile ../../examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
+    \skipto MyStyle::resetTheme
+    \printuntil }
+*/
+QQuickAttachedPropertyPropagator *QQuickAttachedPropertyPropagator::attachedParent() const
+{
+    Q_D(const QQuickAttachedPropertyPropagator);
+    return d->attachedParent;
+}
+
+/*!
+    Finds and sets the attached parent for this attached object, and then does
+    the same for its children. This must be called upon construction of the
+    attached object in order for propagation to work.
+
+    It can be useful to read global/default values before calling this
+    function. For example, before calling \c initialize(), the
+    \l {Imagine Style}{Imagine} style checks a static "globalsInitialized" flag
+    to see if it should read default values from \l QSettings. The values from
+    that file form the basis for any attached property values that have not
+    been explicitly set.
+
+    \quotefromfile ../../examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
+    \skipto MyStyle::MyStyle
+    \printuntil }
+*/
+void QQuickAttachedPropertyPropagator::initialize()
+{
+    Q_D(QQuickAttachedPropertyPropagator);
+    QQuickAttachedPropertyPropagator *attachedParent = findAttachedParent(metaObject(), parent());
+    if (attachedParent)
+        d->setAttachedParent(attachedParent);
+
+    const QList<QQuickAttachedPropertyPropagator *> attachedChildren = findAttachedChildren(metaObject(), parent());
+    for (QQuickAttachedPropertyPropagator *child : attachedChildren)
+        QQuickAttachedPropertyPropagatorPrivate::get(child)->setAttachedParent(this);
+}
+
+/*!
+    This function is called whenever the attached parent of this
+    QQuickAttachedPropertyPropagator changes from \a oldParent to \a newParent.
+
+    Subclasses should reimplement this function to inherit attached properties
+    from \c newParent.
+
+    \quotefromfile ../../examples/quickcontrols2/attachedstyleproperties/MyStyle/mystyle.cpp
+    \skipto attachedParentChange
+    \printuntil }
+    \printuntil }
+*/
+void QQuickAttachedPropertyPropagator::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)
+{
+    Q_UNUSED(newParent);
+    Q_UNUSED(oldParent);
+}
+
+QT_END_NAMESPACE
+
+#include "moc_qquickattachedpropertypropagator.cpp"
diff --git a/src/quickcontrols2/qquickattachedpropertypropagator.h b/src/quickcontrols2/qquickattachedpropertypropagator.h
new file mode 100644
index 0000000000..ec5ff7991a
--- /dev/null
+++ b/src/quickcontrols2/qquickattachedpropertypropagator.h
@@ -0,0 +1,37 @@
+// Copyright (C) 2022 The Qt Company Ltd.
+// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
+
+#ifndef QQUICKATTACHEDOBJECT_H
+#define QQUICKATTACHEDOBJECT_H
+
+#include <QtCore/qobject.h>
+#include <QtQuickControls2/qtquickcontrols2global.h>
+
+QT_BEGIN_NAMESPACE
+
+class QQuickAttachedPropertyPropagatorPrivate;
+
+class Q_QUICKCONTROLS2_EXPORT QQuickAttachedPropertyPropagator : public QObject
+{
+    Q_OBJECT
+
+public:
+    explicit QQuickAttachedPropertyPropagator(QObject *parent = nullptr);
+    ~QQuickAttachedPropertyPropagator();
+
+    QList<QQuickAttachedPropertyPropagator *> attachedChildren() const;
+
+    QQuickAttachedPropertyPropagator *attachedParent() const;
+
+protected:
+    void initialize();
+
+    virtual void attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent);
+
+private:
+    Q_DECLARE_PRIVATE(QQuickAttachedPropertyPropagator)
+};
+
+QT_END_NAMESPACE
+
+#endif // QQUICKATTACHEDOBJECT_H
diff --git a/src/quickcontrols2/universal/qquickuniversalstyle.cpp b/src/quickcontrols2/universal/qquickuniversalstyle.cpp
index 9de295757c..cacf20a75f 100644
--- a/src/quickcontrols2/universal/qquickuniversalstyle.cpp
+++ b/src/quickcontrols2/universal/qquickuniversalstyle.cpp
@@ -118,11 +118,11 @@ static QRgb GlobalBackground = qquickuniversal_light_color(QQuickUniversalStyle:
 static bool HasGlobalForeground = false;
 static bool HasGlobalBackground = false;
 
-QQuickUniversalStyle::QQuickUniversalStyle(QObject *parent) : QQuickAttachedObject(parent),
+QQuickUniversalStyle::QQuickUniversalStyle(QObject *parent) : QQuickAttachedPropertyPropagator(parent),
     m_hasForeground(HasGlobalForeground), m_hasBackground(HasGlobalBackground), m_theme(GlobalTheme),
     m_accent(GlobalAccent), m_foreground(GlobalForeground), m_background(GlobalBackground)
 {
-    init();
+    initialize();
 }
 
 QQuickUniversalStyle *QQuickUniversalStyle::qmlAttachedProperties(QObject *object)
@@ -166,7 +166,7 @@ void QQuickUniversalStyle::inheritTheme(Theme theme)
 void QQuickUniversalStyle::propagateTheme()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickUniversalStyle *universal = qobject_cast<QQuickUniversalStyle *>(child);
         if (universal)
             universal->inheritTheme(m_theme);
@@ -216,7 +216,7 @@ void QQuickUniversalStyle::inheritAccent(QRgb accent)
 void QQuickUniversalStyle::propagateAccent()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickUniversalStyle *universal = qobject_cast<QQuickUniversalStyle *>(child);
         if (universal)
             universal->inheritAccent(m_accent);
@@ -270,7 +270,7 @@ void QQuickUniversalStyle::inheritForeground(QRgb foreground, bool has)
 void QQuickUniversalStyle::propagateForeground()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickUniversalStyle *universal = qobject_cast<QQuickUniversalStyle *>(child);
         if (universal)
             universal->inheritForeground(m_foreground, m_hasForeground);
@@ -325,7 +325,7 @@ void QQuickUniversalStyle::inheritBackground(QRgb background, bool has)
 void QQuickUniversalStyle::propagateBackground()
 {
     const auto styles = attachedChildren();
-    for (QQuickAttachedObject *child : styles) {
+    for (QQuickAttachedPropertyPropagator *child : styles) {
         QQuickUniversalStyle *universal = qobject_cast<QQuickUniversalStyle *>(child);
         if (universal)
             universal->inheritBackground(m_background, m_hasBackground);
@@ -473,7 +473,7 @@ QColor QQuickUniversalStyle::systemColor(SystemColor role) const
     return QColor::fromRgba(m_theme == QQuickUniversalStyle::Dark ? qquickuniversal_dark_color(role) : qquickuniversal_light_color(role));
 }
 
-void QQuickUniversalStyle::attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent)
+void QQuickUniversalStyle::attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent)
 {
     Q_UNUSED(oldParent);
     QQuickUniversalStyle *universal = qobject_cast<QQuickUniversalStyle *>(newParent);
diff --git a/src/quickcontrols2/universal/qquickuniversalstyle_p.h b/src/quickcontrols2/universal/qquickuniversalstyle_p.h
index 7fa6e1a58a..024fde2192 100644
--- a/src/quickcontrols2/universal/qquickuniversalstyle_p.h
+++ b/src/quickcontrols2/universal/qquickuniversalstyle_p.h
@@ -16,13 +16,14 @@
 //
 
 #include <QtGui/qcolor.h>
-#include <QtQuickControls2Impl/private/qquickattachedobject_p.h>
+#include <QtQml/qqml.h>
+#include <QtQuickControls2/qquickattachedpropertypropagator.h>
 
 QT_BEGIN_NAMESPACE
 
 class QQuickUniversalStylePrivate;
 
-class QQuickUniversalStyle : public QQuickAttachedObject
+class QQuickUniversalStyle : public QQuickAttachedPropertyPropagator
 {
     Q_OBJECT
     Q_PROPERTY(Theme theme READ theme WRITE setTheme RESET resetTheme NOTIFY themeChanged FINAL)
@@ -182,7 +183,7 @@ Q_SIGNALS:
     void paletteChanged();
 
 protected:
-    void attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent) override;
+    void attachedParentChange(QQuickAttachedPropertyPropagator *newParent, QQuickAttachedPropertyPropagator *oldParent) override;
 
 private:
     bool variantToRgba(const QVariant &var, const char *name, QRgb *rgba) const;
diff --git a/src/quickcontrols2impl/CMakeLists.txt b/src/quickcontrols2impl/CMakeLists.txt
index 87a5a1634c..acbc91b15e 100644
--- a/src/quickcontrols2impl/CMakeLists.txt
+++ b/src/quickcontrols2impl/CMakeLists.txt
@@ -15,7 +15,6 @@ qt_internal_add_qml_module(QuickControls2Impl
     PLUGIN_TARGET qtquickcontrols2implplugin
     SOURCES
         qquickanimatednode.cpp qquickanimatednode_p.h
-        qquickattachedobject.cpp qquickattachedobject_p.h
         qquickchecklabel.cpp qquickchecklabel_p.h
         qquickclippedtext.cpp qquickclippedtext_p.h
         qquickcolor.cpp qquickcolor_p.h
diff --git a/src/quickcontrols2impl/qquickattachedobject.cpp b/src/quickcontrols2impl/qquickattachedobject.cpp
deleted file mode 100644
index a6bf6fc667..0000000000
--- a/src/quickcontrols2impl/qquickattachedobject.cpp
+++ /dev/null
@@ -1,243 +0,0 @@
-// Copyright (C) 2017 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
-
-#include "qquickattachedobject_p.h"
-
-#include <QtCore/qpointer.h>
-#include <QtQuick/qquickwindow.h>
-#include <QtQuick/private/qquickitem_p.h>
-#include <QtQuick/private/qquickitemchangelistener_p.h>
-#include <QtQuickTemplates2/private/qquickpopup_p.h>
-
-QT_BEGIN_NAMESPACE
-
-static QQuickAttachedObject *attachedObject(const QMetaObject *type, QObject *object, bool create = false)
-{
-    if (!object)
-        return nullptr;
-    auto func = qmlAttachedPropertiesFunction(object, type);
-    return qobject_cast<QQuickAttachedObject *>(qmlAttachedPropertiesObject(object, func, create));
-}
-
-static QQuickAttachedObject *findAttachedParent(const QMetaObject *type, QObject *object)
-{
-    QQuickItem *item = qobject_cast<QQuickItem *>(object);
-    if (item) {
-        // lookup parent items and popups
-        QQuickItem *parent = item->parentItem();
-        while (parent) {
-            QQuickAttachedObject *attached = attachedObject(type, parent);
-            if (attached)
-                return attached;
-
-            QQuickPopup *popup = qobject_cast<QQuickPopup *>(parent->parent());
-            if (popup)
-                return attachedObject(type, popup);
-
-            parent = parent->parentItem();
-        }
-
-        // fallback to item's window
-        QQuickAttachedObject *attached = attachedObject(type, item->window());
-        if (attached)
-            return attached;
-    } else {
-        // lookup popup's window
-        QQuickPopup *popup = qobject_cast<QQuickPopup *>(object);
-        if (popup)
-            return attachedObject(type, popup->popupItem()->window());
-    }
-
-    // lookup parent window
-    QQuickWindow *window = qobject_cast<QQuickWindow *>(object);
-    if (window) {
-        QQuickWindow *parentWindow = qobject_cast<QQuickWindow *>(window->parent());
-        if (parentWindow) {
-            QQuickAttachedObject *attached = attachedObject(type, window);
-            if (attached)
-                return attached;
-        }
-    }
-
-    // fallback to engine (global)
-    if (object) {
-        QQmlEngine *engine = qmlEngine(object);
-        if (engine) {
-            QByteArray name = QByteArray("_q_") + type->className();
-            QQuickAttachedObject *attached = engine->property(name).value<QQuickAttachedObject *>();
-            if (!attached) {
-                attached = attachedObject(type, engine, true);
-                engine->setProperty(name, QVariant::fromValue(attached));
-            }
-            return attached;
-        }
-    }
-
-    return nullptr;
-}
-
-static QList<QQuickAttachedObject *> findAttachedChildren(const QMetaObject *type, QObject *object)
-{
-    QList<QQuickAttachedObject *> children;
-
-    QQuickItem *item = qobject_cast<QQuickItem *>(object);
-    if (!item) {
-        QQuickWindow *window = qobject_cast<QQuickWindow *>(object);
-        if (window) {
-            item = window->contentItem();
-
-            const auto &windowChildren = window->children();
-            for (QObject *child : windowChildren) {
-                QQuickWindow *childWindow = qobject_cast<QQuickWindow *>(child);
-                if (childWindow) {
-                    QQuickAttachedObject *attached = attachedObject(type, childWindow);
-                    if (attached)
-                        children += attached;
-                }
-            }
-        }
-    }
-
-    if (item) {
-        const auto childItems = item->childItems();
-        for (QQuickItem *child : childItems) {
-            QQuickAttachedObject *attached = attachedObject(type, child);
-            if (attached)
-                children += attached;
-            else
-                children += findAttachedChildren(type, child);
-        }
-    }
-
-    return children;
-}
-
-static QQuickItem *findAttachedItem(QObject *parent)
-{
-    QQuickItem *item = qobject_cast<QQuickItem *>(parent);
-    if (!item) {
-        QQuickPopup *popup = qobject_cast<QQuickPopup *>(parent);
-        if (popup)
-            item = popup->popupItem();
-    }
-    return item;
-}
-
-class QQuickAttachedObjectPrivate : public QObjectPrivate, public QQuickItemChangeListener
-{
-public:
-    Q_DECLARE_PUBLIC(QQuickAttachedObject)
-
-    static QQuickAttachedObjectPrivate *get(QQuickAttachedObject *attachedObject)
-    {
-        return attachedObject->d_func();
-    }
-
-    void attachTo(QObject *object);
-    void detachFrom(QObject *object);
-
-    void itemWindowChanged(QQuickWindow *window);
-    void itemParentChanged(QQuickItem *item, QQuickItem *parent) override;
-
-    QList<QQuickAttachedObject *> attachedChildren;
-    QPointer<QQuickAttachedObject> attachedParent;
-};
-
-void QQuickAttachedObjectPrivate::attachTo(QObject *object)
-{
-    QQuickItem *item = findAttachedItem(object);
-    if (item) {
-        connect(item, &QQuickItem::windowChanged, this, &QQuickAttachedObjectPrivate::itemWindowChanged);
-        QQuickItemPrivate::get(item)->addItemChangeListener(this, QQuickItemPrivate::Parent);
-    }
-}
-
-void QQuickAttachedObjectPrivate::detachFrom(QObject *object)
-{
-    QQuickItem *item = findAttachedItem(object);
-    if (item) {
-        disconnect(item, &QQuickItem::windowChanged, this, &QQuickAttachedObjectPrivate::itemWindowChanged);
-        QQuickItemPrivate::get(item)->removeItemChangeListener(this, QQuickItemPrivate::Parent);
-    }
-}
-
-void QQuickAttachedObjectPrivate::itemWindowChanged(QQuickWindow *window)
-{
-    Q_Q(QQuickAttachedObject);
-    QQuickAttachedObject *attachedParent = nullptr;
-    QQuickItem *item = qobject_cast<QQuickItem *>(q->sender());
-    if (item)
-        attachedParent = findAttachedParent(q->metaObject(), item);
-    if (!attachedParent)
-        attachedParent = attachedObject(q->metaObject(), window);
-    q->setAttachedParent(attachedParent);
-}
-
-void QQuickAttachedObjectPrivate::itemParentChanged(QQuickItem *item, QQuickItem *parent)
-{
-    Q_Q(QQuickAttachedObject);
-    Q_UNUSED(parent);
-    q->setAttachedParent(findAttachedParent(q->metaObject(), item));
-}
-
-QQuickAttachedObject::QQuickAttachedObject(QObject *parent)
-    : QObject(*(new QQuickAttachedObjectPrivate), parent)
-{
-    Q_D(QQuickAttachedObject);
-    d->attachTo(parent);
-}
-
-QQuickAttachedObject::~QQuickAttachedObject()
-{
-    Q_D(QQuickAttachedObject);
-    d->detachFrom(parent());
-    setAttachedParent(nullptr);
-}
-
-QList<QQuickAttachedObject *> QQuickAttachedObject::attachedChildren() const
-{
-    Q_D(const QQuickAttachedObject);
-    return d->attachedChildren;
-}
-
-QQuickAttachedObject *QQuickAttachedObject::attachedParent() const
-{
-    Q_D(const QQuickAttachedObject);
-    return d->attachedParent;
-}
-
-void QQuickAttachedObject::setAttachedParent(QQuickAttachedObject *parent)
-{
-    Q_D(QQuickAttachedObject);
-    if (d->attachedParent == parent)
-        return;
-
-    QQuickAttachedObject *oldParent = d->attachedParent;
-    if (d->attachedParent)
-        QQuickAttachedObjectPrivate::get(d->attachedParent)->attachedChildren.removeOne(this);
-    d->attachedParent = parent;
-    if (parent)
-        QQuickAttachedObjectPrivate::get(parent)->attachedChildren.append(this);
-    attachedParentChange(parent, oldParent);
-}
-
-void QQuickAttachedObject::init()
-{
-    QQuickAttachedObject *attachedParent = findAttachedParent(metaObject(), parent());
-    if (attachedParent)
-        setAttachedParent(attachedParent);
-
-    const QList<QQuickAttachedObject *> attachedChildren = findAttachedChildren(metaObject(), parent());
-    for (QQuickAttachedObject *child : attachedChildren)
-        child->setAttachedParent(this);
-}
-
-void QQuickAttachedObject::attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent)
-{
-    Q_UNUSED(newParent);
-    Q_UNUSED(oldParent);
-}
-
-QT_END_NAMESPACE
-
-#include "moc_qquickattachedobject_p.cpp"
diff --git a/src/quickcontrols2impl/qquickattachedobject_p.h b/src/quickcontrols2impl/qquickattachedobject_p.h
deleted file mode 100644
index 3473c16936..0000000000
--- a/src/quickcontrols2impl/qquickattachedobject_p.h
+++ /dev/null
@@ -1,51 +0,0 @@
-// Copyright (C) 2017 The Qt Company Ltd.
-// SPDX-License-Identifier: LicenseRef-Qt-Commercial OR LGPL-3.0-only OR GPL-2.0-only OR GPL-3.0-only
-
-#ifndef QQUICKATTACHEDOBJECT_P_H
-#define QQUICKATTACHEDOBJECT_P_H
-
-//
-//  W A R N I N G
-//  -------------
-//
-// This file is not part of the Qt API.  It exists purely as an
-// implementation detail.  This header file may change from version to
-// version without notice, or even be removed.
-//
-// We mean it.
-//
-
-#include <QtQml/qqml.h>
-#include <QtCore/qobject.h>
-#include <QtQuickControls2Impl/private/qtquickcontrols2implglobal_p.h>
-
-QT_BEGIN_NAMESPACE
-
-class QQuickAttachedObjectPrivate;
-
-class Q_QUICKCONTROLS2IMPL_PRIVATE_EXPORT QQuickAttachedObject : public QObject
-{
-    Q_OBJECT
-
-public:
-    explicit QQuickAttachedObject(QObject *parent = nullptr);
-    ~QQuickAttachedObject();
-
-    QList<QQuickAttachedObject *> attachedChildren() const;
-
-    QQuickAttachedObject *attachedParent() const;
-    void setAttachedParent(QQuickAttachedObject *parent);
-
-protected:
-    void init();
-
-    virtual void attachedParentChange(QQuickAttachedObject *newParent, QQuickAttachedObject *oldParent);
-
-private:
-    Q_DISABLE_COPY(QQuickAttachedObject)
-    Q_DECLARE_PRIVATE(QQuickAttachedObject)
-};
-
-QT_END_NAMESPACE
-
-#endif // QQUICKATTACHEDOBJECT_P_H
diff --git a/tests/auto/quickcontrols2/qquickmaterialstyle/data/tst_material.qml b/tests/auto/quickcontrols2/qquickmaterialstyle/data/tst_material.qml
index 689d90ca25..34754420d0 100644
--- a/tests/auto/quickcontrols2/qquickmaterialstyle/data/tst_material.qml
+++ b/tests/auto/quickcontrols2/qquickmaterialstyle/data/tst_material.qml
@@ -275,49 +275,199 @@ TestCase {
         compare(popupObject.label2.color.toString(), popupObject.Material.textSelectionColor.toString())
     }
 
-    function test_window() {
-        let parent = createTemporaryObject(windowComponent)
-
-        let control = button.createObject(parent.contentItem)
-        compare(control.Material.primary, parent.Material.primary)
-        compare(control.Material.accent, parent.Material.accent)
-        compare(control.Material.background, parent.Material.background)
-        compare(control.Material.foreground, parent.Material.foreground)
-        compare(control.Material.theme, parent.Material.theme)
-
-        let styledChild = styledWindowComponent.createObject(parent)
-        verify(styledChild.Material.primary !== parent.Material.primary)
-        verify(styledChild.Material.accent !== parent.Material.accent)
-        verify(styledChild.Material.background !== parent.Material.background)
-        verify(styledChild.Material.foreground !== parent.Material.foreground)
-        verify(styledChild.Material.theme !== parent.Material.theme)
-
-        let unstyledChild = windowComponent.createObject(parent)
-        compare(unstyledChild.Material.primary, parent.Material.primary)
-        compare(unstyledChild.Material.accent, parent.Material.accent)
-        compare(unstyledChild.Material.background, parent.Material.background)
-        compare(unstyledChild.Material.foreground, parent.Material.foreground)
-        compare(unstyledChild.Material.theme, parent.Material.theme)
-
-        parent.Material.primary = Material.Lime
+    component StyledChildWindow: Window {
+        objectName: "styledChildWindow"
+
+        Material.objectName: objectName + "MaterialAttached"
+        Material.theme: Material.Dark
+        Material.primary: Material.Brown
+        Material.accent: Material.Green
+        Material.background: Material.Yellow
+        Material.foreground: Material.Grey
+    }
+
+    component StyledChildAppWindow: ApplicationWindow {
+        objectName: "styledChildAppWindow"
+
+        Material.objectName: objectName + "MaterialAttached"
+        Material.theme: Material.Dark
+        Material.primary: Material.Brown
+        Material.accent: Material.Green
+        Material.background: Material.Yellow
+        Material.foreground: Material.Grey
+    }
+
+    component UnstyledChildWindow: Window {
+        objectName: "unstyledChildWindow"
+        Material.objectName: objectName + "MaterialAttached"
+    }
+
+    component UnstyledChildAppWindow: ApplicationWindow {
+        objectName: "unstyledChildAppWindow"
+        Material.objectName: objectName + "MaterialAttached"
+    }
+
+    Component {
+        id: parentWindowComponent
+
+        Window {
+            objectName: "rootWindow"
+
+            Material.objectName: objectName + "MaterialAttached"
+
+            property alias styledChildWindow: styledChildWindow
+            property alias unstyledChildWindow: unstyledChildWindow
+
+            StyledChildWindow {
+                id: styledChildWindow
+            }
+
+            UnstyledChildWindow {
+                id: unstyledChildWindow
+            }
+        }
+    }
+
+    Component {
+        id: parentAppWindowComponent
+
+        ApplicationWindow {
+            objectName: "rootAppWindow"
+
+            Material.objectName: objectName + "MaterialAttached"
+
+            property alias styledChildWindow: styledChildWindow
+            property alias unstyledChildWindow: unstyledChildWindow
+
+            StyledChildAppWindow {
+                id: styledChildWindow
+            }
+
+            UnstyledChildAppWindow {
+                id: unstyledChildWindow
+            }
+        }
+    }
+
+    Component {
+        id: parentMixed1WindowComponent
+
+        ApplicationWindow {
+            objectName: "rootAppWindow"
+
+            Material.objectName: objectName + "MaterialAttached"
+
+            property alias styledChildWindow: styledChildWindow
+            property alias unstyledChildWindow: unstyledChildWindow
+
+            StyledChildWindow {
+                id: styledChildWindow
+            }
+
+            UnstyledChildWindow {
+                id: unstyledChildWindow
+            }
+        }
+    }
+
+    Component {
+        id: parentMixed2WindowComponent
+
+        Window {
+            id: rootWindow
+            objectName: "rootWindow"
+
+            Material.objectName: objectName + "MaterialAttached"
+
+            property alias styledChildWindow: styledChildWindow
+            property alias unstyledChildWindow: unstyledChildWindow
+
+            StyledChildAppWindow {
+                id: styledChildWindow
+            }
+
+            UnstyledChildAppWindow {
+                id: unstyledChildWindow
+            }
+        }
+    }
+
+    function test_window_data() {
+        return [
+            { tag: "Window", component: parentWindowComponent },
+            { tag: "ApplicationWindow", component: parentAppWindowComponent },
+            // Test a combination of Window and ApplicationWindow.
+            { tag: "mixed-1", component: parentMixed1WindowComponent },
+            { tag: "mixed-2", component: parentMixed2WindowComponent },
+        ]
+    }
+
+    function test_window(data) {
+        let parentWindow = createTemporaryObject(data.component, null)
+        verify(parentWindow)
+
+        let control = button.createObject(parentWindow.contentItem)
+        verify(control)
+        compare(control.Material.primary, parentWindow.Material.primary)
+        compare(control.Material.accent, parentWindow.Material.accent)
+        compare(control.Material.background, parentWindow.Material.background)
+        compare(control.Material.foreground, parentWindow.Material.foreground)
+        compare(control.Material.theme, parentWindow.Material.theme)
+
+        let styledChildWindow = parentWindow.styledChildWindow
+        verify(styledChildWindow)
+        verify(styledChildWindow.Material.primary !== parentWindow.Material.primary)
+        verify(styledChildWindow.Material.accent !== parentWindow.Material.accent)
+        verify(styledChildWindow.Material.background !== parentWindow.Material.background)
+        verify(styledChildWindow.Material.foreground !== parentWindow.Material.foreground)
+        verify(styledChildWindow.Material.theme !== parentWindow.Material.theme)
+
+        let unstyledChildWindow = parentWindow.unstyledChildWindow
+        verify(unstyledChildWindow)
+        compare(unstyledChildWindow.Material.primary, parentWindow.Material.primary)
+        compare(unstyledChildWindow.Material.accent, parentWindow.Material.accent)
+        compare(unstyledChildWindow.Material.background, parentWindow.Material.background)
+        compare(unstyledChildWindow.Material.foreground, parentWindow.Material.foreground)
+        compare(unstyledChildWindow.Material.theme, parentWindow.Material.theme)
+
+        parentWindow.Material.primary = Material.Lime
         compare(control.Material.primary, Material.color(Material.Lime))
-        verify(styledChild.Material.primary !== Material.color(Material.Lime))
-        // ### TODO: compare(unstyledChild.Material.primary, Material.color(Material.Lime))
+        verify(styledChildWindow.Material.primary !== Material.color(Material.Lime))
+        compare(unstyledChildWindow.Material.primary, Material.color(Material.Lime))
 
-        parent.Material.accent = Material.Cyan
+        parentWindow.Material.accent = Material.Cyan
         compare(control.Material.accent, Material.color(Material.Cyan))
-        verify(styledChild.Material.accent !== Material.color(Material.Cyan))
-        // ### TODO: compare(unstyledChild.Material.accent, Material.color(Material.Cyan))
+        verify(styledChildWindow.Material.accent !== Material.color(Material.Cyan))
+        compare(unstyledChildWindow.Material.accent, Material.color(Material.Cyan))
 
-        parent.Material.background = Material.Indigo
+        parentWindow.Material.background = Material.Indigo
         compare(control.Material.background, Material.color(Material.Indigo))
-        verify(styledChild.Material.background !== Material.color(Material.Indigo))
-        // ### TODO: compare(unstyledChild.Material.background, Material.color(Material.Indigo))
+        verify(styledChildWindow.Material.background !== Material.color(Material.Indigo))
+        compare(unstyledChildWindow.Material.background, Material.color(Material.Indigo))
 
-        parent.Material.foreground = Material.Pink
+        parentWindow.Material.foreground = Material.Pink
         compare(control.Material.foreground, Material.color(Material.Pink))
-        verify(styledChild.Material.foreground !== Material.color(Material.Pink))
-        // ### TODO: compare(unstyledChild.Material.foreground, Material.color(Material.Pink))
+        verify(styledChildWindow.Material.foreground !== Material.color(Material.Pink))
+        compare(unstyledChildWindow.Material.foreground, Material.color(Material.Pink))
+
+        // Test that theme changes are propagated to child windows.
+        // Make sure that this check actually does something (in case the default changes).
+        compare(parentWindow.Material.theme, Material.Light)
+        // styledChildWindow was already dark, so make it light to verify that it doesn't change.
+        styledChildWindow.Material.theme = Material.Light
+        // Reset background since Theme affects it and we use it to test that the colors change.
+        parentWindow.Material.background = undefined
+        // Setting theme to Dark should result in the background colors of control and unstyledChildWindow changing.
+        // Note that since Window is unstyled, its actual (background) color won't change.
+        parentWindow.Material.theme = Material.Dark
+        compare(control.Material.theme, Material.Dark)
+        compare(styledChildWindow.Material.theme, Material.Light)
+        compare(unstyledChildWindow.Material.theme, Material.Dark)
+        // Make sure that the colors actually changed.
+        compare(parentWindow.Material.background, Qt.color("#303030"))
+        compare(control.Material.background, parentWindow.Material.background)
+        verify(styledChildWindow.Material.background !== parentWindow.Material.background)
+        compare(unstyledChildWindow.Material.background, parentWindow.Material.background)
     }
 
     function test_loader() {