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调用WindowManager，并设置WindowManager.LayoutParams的相关属性，通过WindowManager的addView方法创建View，这样产生出来的View根据WindowManager.LayoutParams属性不同，效果也就不同了。比如创建系统顶级窗口，实现悬浮窗口效果！

WindowManager的方法很简单，基本用到的就三个addView，removeView，updateViewLayout。

而WindowManager.LayoutParams的属性就多了，非常丰富，具体请查看SDK文档。这里给出Android中的WindowManager.java源码，可以具体看一下。

下面是简单示例代码：

public class myFloatView extends Activity {
    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        Button bb=new Button(getApplicationContext());
        WindowManager wm=(WindowManager)getApplicationContext().getSystemService("window");
        WindowManager.LayoutParams wmParams = new WindowManager.LayoutParams();
        /**
         *以下都是WindowManager.LayoutParams的相关属性
         * 具体用途请参考SDK文档
         */
        wmParams.type=2002;   //这里是关键，你也可以试试2003
        wmParams.format=1;
         /**
         *这里的flags也很关键
         *代码实际是wmParams.flags |= FLAG_NOT_FOCUSABLE;
         *40的由来是wmParams的默认属性（32）+ FLAG_NOT_FOCUSABLE（8）
         */
        wmParams.flags=40;    
        wmParams.width=40;
        wmParams.height=40;
        wm.addView(bb, wmParams);  //创建View
    }
}

别忘了在AndroidManifest.xml中添加权限：

<uses-permission android:name="android.permission.SYSTEM_ALERT_WINDOW" />

PS:这里举例说明一下type的值的意思：

        /**
         * Window type: phone.  These are non-application windows providing
         * user interaction with the phone (in particular incoming calls).
         * These windows are normally placed above all applications, but behind
         * the status bar.
         */
        public static final int TYPE_PHONE              = FIRST_SYSTEM_WINDOW+2;
        /**
         * Window type: system window, such as low power alert. These windows
         * are always on top of application windows.
         */
        public static final int TYPE_SYSTEM_ALERT       = FIRST_SYSTEM_WINDOW+3;

这个FIRST_SYSTEM_WINDOW的值就是2000。2003和2002的区别就在于2003类型的View比2002类型的还要top，能显示在系统下拉状态栏之上！