android的window

　原来，整个 Android的窗口机制是基于一个叫做 WindowManager，这个接口可以添加view到屏幕，也可以从屏幕删除view。它面向的对象一端是屏幕，另一端就是View，直接忽略我们以前的Activity或者Dialog之类的东东。其实我们的Activity 或者Diolog底层的实现也是通过WindowManager，这个 WindowManager是全局的，整个系统就是这个唯一的东东。它是显示 View的最底层了。但是要注意，显示出来就要销毁掉，这个是必须的，销毁其实就是一个remove

Android中悬浮窗口的实现原理和示例代码
http://www.xsmile.net/?p=404

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：
http://www.netmite.com/android/mydroid/frameworks/base/core/java/android/view/WindowManager.java

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();
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。
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
}
}

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：

<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

http://www.cnblogs.com/GnagWang/archive/2011/02/06/1949569.html

http://gundumw100.javaeye.com/blog/899977

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