C# 在switch中调用枚举

书上的代码，没写全，switch(connectionState2)会一直显示
/使用了没有赋值的局部变量connectionState2/

 ConnectionState connectionState;
            //...
            switch (connectionState)
            {
                case ConnectionState.Connected:
                    //...
                    break;
                case ConnectionState.Connecting:
                    //...
                    break;
                case ConnectionState.Disconnected:
                   // ...
                    break;
                case ConnectionState.Disconnecting:
                    //...
                    break;
            }

enum ConnectionState
    {
        Disconnected,
        Connecting,
        Connected,
        Disconnecting
    }

补加一个，两个是一起的是为了显示出使用枚举的话可读性更强，
两者在运行时性能完全一样(改了一下枚举定义的一点问题)。

 //比较整数switch和枚举switch
            int connectionState;
            //...

            switch (connectionState)
            {
                case 0:
                    //...
                    break;
                case 1:
                    //...
                    break;
                case 2:
                    //...
                    break;
                case 3:
                    //...
                    break;
            }

求使用枚举的switch语句如何调用