安卓WebView加载不出指定网页

package com.example.webviewdemo;

import android.support.v7.app.ActionBarActivity;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.Window;
import android.webkit.WebChromeClient;
import android.webkit.WebSettings;
import android.webkit.WebView;
import android.webkit.WebViewClient;
import android.widget.EditText;
import android.widget.ImageButton;
import android.widget.ProgressBar;
import android.widget.Toast;
import android.annotation.SuppressLint;
import android.os.Bundle;

public class MainActivity extends ActionBarActivity {

private WebView webview;
private ProgressBar pb;
private EditText edt;
private ImageButton refresh;
private ImageButton go;
private String url;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);        
    setContentView(R.layout.activity_main);
    init();

}

@SuppressLint("SetJavaScriptEnabled") 
private void init() {
    // TODO Auto-generated method stub
    //进度条绑定视图，并设置进度条的最大值
    pb = (ProgressBar) findViewById(R.id.pb);  
    pb.setMax(100);  

    //EditText绑定视图
    edt=(EditText) findViewById(R.id.edt);
    url=edt.getText().toString();

    //imageButton绑定视图
    //刷新按钮
    refresh=(ImageButton) findViewById(R.id.refresh);
    refresh.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            webview.loadUrl(webview.getUrl());
            Toast.makeText(MainActivity.this, "刷新", Toast.LENGTH_SHORT).show();
        }
    });
    //跳转按钮
    go=(ImageButton) findViewById(R.id.go);
    go.setOnClickListener(new OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            webview.loadUrl(url);

            Toast.makeText(MainActivity.this, "跳转", Toast.LENGTH_SHORT).show();
        }
    });

    //绑定WebView视图
    webview=(WebView) findViewById(R.id.webview);
    //WebView加载web资源，同时也可以加载本地资源，将写好的HTML文件放在assets文件夹下，然后调用即可

// webview.loadUrl(url);
webview.setWebChromeClient(new WebChromeClient() {

        @Override
         public void onProgressChanged(WebView view, int newProgress) {

            if (newProgress == 100) {
                 pb.setVisibility(View.GONE);
             } else {

// if (View.INVISIBLE == pb.getVisibility()) {
pb.setVisibility(View.VISIBLE);
// }
pb.setProgress(newProgress);
}
super.onProgressChanged(view, newProgress);
}

});

    //覆盖WebView默认从第三方浏览器打开网页的行为，直接从WebView中打开网页
    webview.setWebViewClient(new WebViewClient(){
    @Override
    public boolean shouldOverrideUrlLoading(WebView view, String url) {
        // TODO Auto-generated method stub
            view.loadUrl(edt.getText().toString());
            return true;
    }
         //WebViewClient帮助WebView去处理一些网页控制和请求
    });
    //设置启用javaScript
    WebSettings websetting=webview.getSettings();
    websetting.setJavaScriptEnabled(true);
    websetting.setSupportZoom(true);
    websetting.setUseWideViewPort(true);
    websetting.setCacheMode(WebSettings.LOAD_CACHE_ELSE_NETWORK);


}
//设置点击返回键返回上一个页面
@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    // TODO Auto-generated method stub
    if(keyCode == KeyEvent.KEYCODE_BACK && webview.canGoBack()){
        webview.goBack();
        return true;
    }
    return super.onKeyDown(keyCode, event);
}

}

xml代码：
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
>
android:id="@+id/pb"
style="?android:attr/progressBarStyleHorizontal"
android:layout_width="match_parent"
android:layout_height="8dip"
android:indeterminateOnly="false"
android:max="100"
android:progressDrawable="@drawable/progress_bar_states"
/>

<LinearLayout 
    android:layout_width="match_parent"
    android:layout_height="40dip"
    android:orientation="horizontal"
    android:background="@drawable/title_bg">

<EditText 
    android:id="@+id/edt"
    android:layout_width="match_parent"
    android:layout_height="40dp"
    android:layout_weight="3"
    android:textColor="#000"
    android:hint="@string/edittext"/>

android:id="@+id/refresh"
android:layout_width="50dp"
android:layout_height="40dp"
android:layout_marginLeft="5dp"
android:layout_marginRight="5dp"
android:layout_weight="1"
android:background="@drawable/refresh"
android:contentDescription="@null"
/>
android:id="@+id/go"
android:layout_width="50dp"
android:layout_height="40dp"
android:layout_weight="1"
android:background="@drawable/go"
android:contentDescription="@null"
/>

<WebView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/webview" />

功能是在输入框中输入网址，然后点击跳转会跳转到指定网页，不知道为什么网页就是加载不出来，百度了半天没个结果。。。求解答