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。 
WindowManager 的源码地址： 
 

以下代码请仅供演示：

Java代码  

1. public class myFloatView extends Activity {  
2.     /** Called when the activity is first created. */  
3.     @Override  
4.     public void onCreate(Bundle savedInstanceState) {  
5.         super.onCreate(savedInstanceState);  
6.         setContentView(R.layout.main);  
7.         Button bb=new Button(getApplicationContext());  
8.         WindowManager wm=(WindowManager)getApplicationContext().getSystemService("window");  
9.         WindowManager.LayoutParams wmParams = new WindowManager.LayoutParams();  
10.         wmParams.type=2002;  //type是关键，这里的2002表示系统级窗口，你也可以试试2003。  
11.         wmParams.format=1;  
12.         /** 
13.          *这里的flags也很关键 
14.          *代码实际是wmParams.flags |= FLAG_NOT_FOCUSABLE; 
15.          *40的由来是wmParams的默认属性（32）+ FLAG_NOT_FOCUSABLE（8） 
16.          */  
17.         wmParams.flags=40;  
18.         wmParams.width=40;  
19.         wmParams.height=40;  
20.         wm.addView(bb, wmParams);//创建View  
21.     }  
22. }  

PS：本代码在Android2.3下测试无错（从API Level来看，实际上android1.5都可行）！另外别忘了在AndroidManifest.xml文件中加入如下权限：

Xml代码  

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

关于代码中wmParams.type的值的问题，下面给出一些数值参考： 
/** 
         * Window type: the status bar.  There can be only one status bar 
         * window; it is placed at the top of the screen, and all other 
         * windows are shifted down so they are below it. 
         */ 
        public static final int TYPE_STATUS_BAR         = FIRST_SYSTEM_WINDOW; 
    
        /** 
         * Window type: the search bar.  There can be only one search bar 
         * window; it is placed at the top of the screen. 
         */ 
        public static final int TYPE_SEARCH_BAR         = FIRST_SYSTEM_WINDOW+1; 
    
        /** 
         * 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; 
        
        /** 
         * Window type: keyguard window. 
         */ 
        public static final int TYPE_KEYGUARD           = FIRST_SYSTEM_WINDOW+4; 
        
        /** 
         * Window type: transient notifications. 
         */ 
        public static final int TYPE_TOAST              = FIRST_SYSTEM_WINDOW+5; 
        
        /** 
         * Window type: system overlay windows, which need to be displayed 
         * on top of everything else.  These windows must not take input 
         * focus, or they will interfere with the keyguard. 
         */ 
        public static final int TYPE_SYSTEM_OVERLAY     = FIRST_SYSTEM_WINDOW+6; 
        
        /** 
         * Window type: priority phone UI, which needs to be displayed even if 
         * the keyguard is active.  These windows must not take input 
         * focus, or they will interfere with the keyguard. 
         */ 
        public static final int TYPE_PRIORITY_PHONE     = FIRST_SYSTEM_WINDOW+7; 
        
        /** 
         * Window type: panel that slides out from the status bar 
         */ 
        public static final int TYPE_STATUS_BAR_PANEL   = FIRST_SYSTEM_WINDOW+8; 
        
        /** 
         * Window type: panel that slides out from the status bar 
         */ 
        public static final int TYPE_SYSTEM_DIALOG      = FIRST_SYSTEM_WINDOW+8; 
    
        /** 
         * Window type: dialogs that the keyguard shows 
         */ 
        public static final int TYPE_KEYGUARD_DIALOG    = FIRST_SYSTEM_WINDOW+9; 
        
        /** 
         * Window type: internal system error windows, appear on top of 
         * everything they can. 
         */ 
        public static final int TYPE_SYSTEM_ERROR       = FIRST_SYSTEM_WINDOW+10; 
        
        /** 
         * End of types of system windows. 
         */ 
        public static final int LAST_SYSTEM_WINDOW      = 2999; 

--------------------------------- 
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！ 

    可以看出来，2002的值的含义其实就是2000+2。数值2000的含义就是系统级窗口，2002和2003的区别就是 2003 比 2002还要更上一层！比如，type为2003的view，能显示在手机下拉状态栏之上！ 

而关于flags等其他的属性请参考SDK文档 

Android悬浮窗体 
 
Android中悬浮窗口的实现原理和示例代码 
 

Android中可自由移动悬浮窗口的Demo 
/a> 
前段时间捣鼓出Android悬浮窗口的实现，今天抽空写了一个可自由移动悬浮窗口的Demo。 

简要说明如下： 

1、通过覆写悬浮View中onTouchEvent方法实现自由移动悬浮窗口。 

2、悬浮窗口坐标的移动实际是windowMananager.LayoutParams中x和y的变换，但是要注意设置相应的gravity。 

3、用windowManager创建的View，当不需要时，务必记住使用windowManager的removeView方法来移除，请在Activity相关生命周期中自行添加扫尾工作。 

4、代码中已经附上详细注释。有关参数具体含义，请自行参考SDK。 

=============================== 

注意Demo中wmParams.format=1的属性（我源码中打了双斜杠），如果启用，图片背景将会透明，效果图如下： 


================================ 

一些说明： 

对于种种原因没有查看SDK文档的一些朋友，可能对我源码中wmParams.type=2002这样的语句不太了解其2002的具体意义，给出可读性好点的语句。 

Java代码  

1. wmParams.type=LayoutParams.TYPE_PHONE;   
2.        //wmParams.format=PixelFormat.RGBA_8888;   //设置图片格式，效果为背景透明  
3.        wmParams.flags=LayoutParams.FLAG_NOT_TOUCH_MODAL  
4.                              | LayoutParams.FLAG_NOT_FOCUSABLE;  
5.        /* 
6.         * 下面的flags属性的效果形同“锁定”。 
7.         * 悬浮窗不可触摸，不接受任何事件,同时不影响后面的事件响应。 
8.         wmParams.flags=LayoutParams.FLAG_NOT_TOUCH_MODAL  
9.                               | LayoutParams.FLAG_NOT_FOCUSABLE 
10.                               | LayoutParams.FLAG_NOT_TOUCHABLE; 
11.        */  

附Demo源码： 

Android中悬浮窗口 
http://www.cnblogs.com/GnagWang/archive/2011/02/06/1949569.html