Android 源碼分析Notification的notify

在上一篇文章Android獲取第三方音樂播放器的音樂信息的末尾，提到可以通過捕獲第三方音樂發送的的Notification，來獲取到當前播放的歌曲的信息。先分析下Notification的更新機制。

涉及Service:

 StatusBarManagerService

NotificationManagerService

這個兩個service都會在frameworks/base/services/java/com/android/server/SystemServer.java文件裡面進行啟動的

class ServerThread extends Thread {  
 public void run() {
......
     StatusBarManagerService statusBar = null;
     NotificationManagerService notification = null;
......
    statusBar = new StatusBarManagerService(context, wm);
    ServiceManager.addService(Context.STATUS_BAR_SERVICE, statusBar);
......
    notification = new NotificationManagerService(context, statusBar, lights);                   
    ServiceManager.addService(Context.NOTIFICATION_SERVICE, notification);

......
 
   }

}

下面開始跟蹤Notification的Notify流程。

1.

當在Activity裡面創建一個Notification，並Notify

NotificationManager nm = (NotificationManager)getSystemService(Context.NOTIFICATION_SERVICE);               
Notification n = new Notification(R.drawable.chat, "Hello,there!", System.currentTimeMillis());             
n.flags = Notification.FLAG_AUTO_CANCEL;                
Intent i = new Intent(arg0.getContext(), NotificationShow.class);
i.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP|Intent.FLAG_ACTIVITY_NEW_TASK);           
//PendingIntent
PendingIntent contentIntent = PendingIntent.getActivity(
        arg0.getContext(), 
        R.string.app_name, 
        i, 
        PendingIntent.FLAG_UPDATE_CURRENT);
                 
n.setLatestEventInfo(
        arg0.getContext(),
        "Hello,there!", 
        "Hello,there,I'm john.", 
        contentIntent);
nm.notify(R.string.app_name, n);

2.調用NotificationManager.notify,進入notify 方法

 public void notify(int id, Notification notification)
    {
        notify(null, id, notification);
    }

 public void notify(String tag, int id, Notification notification)
    {
......
         INotificationManager service = getService();

......
         service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id,
              notification, idOut, UserHandle.myUserId());
......         
 }

3.在調用notify(String tag, int id, Notification notification)時，會調用getService()

static public INotificationManager getService()
78    {
79        if (sService != null) {
80            return sService;
81        }
82        IBinder b = ServiceManager.getService("notification");
83        sService = INotificationManager.Stub.asInterface(b);
84        return sService;
85    }

這裡發現，會調用ServiceManager.getService("notification"), 這樣就會獲取到文章剛開始講的NotificationManagerService 的一個binder對象。獲取回到第二步調用service.enqueueNotificationWithTAG.

4.進入NotificationManagerService的enqueueNotificationWithTAG

public void enqueueNotificationWithTag(String pkg, String basePkg, String tag, int id,
1621            Notification notification, int[] idOut, int userId)
1622    {
1623        enqueueNotificationInternal(pkg, basePkg, Binder.getCallingUid(), Binder.getCallingPid(),
1624                tag, id, notification, idOut, userId);
1625    }

1634    public void enqueueNotificationInternal(final String pkg, String basePkg, final int callingUid,
1635            final int callingPid, final String tag, final int id, final Notification notification,
1636            int[] idOut, int incomingUserId)
1637    {
......
		final StatusBarNotification n = new StatusBarNotification(
1755                            pkg, id, tag, callingUid, callingPid, score, notification, user);

1792                                mStatusBar.updateNotification(r.statusBarKey, n);
1793                           
......
         }

在這個方法裡，會將前面傳遞進來的Notification封裝成一個StatusBarNotification對象，然後調用mStatusBar.updateNotification去更新,這個mStatusBar是什麼？

5. 文章最開始提到會在ServerThread裡面添加NotificationManagerService，在創建的NotificationManagerService的時候，會調用它的構造函數

 NotificationManagerService(Context context, StatusBarManagerService statusBar,
1291            LightsService lights)
1292    {
       	....... 
	}

這裡面就會傳遞進來，在ServerThread裡剛剛創建的StatusBarManagerService. 所以在第4步的時候我們能夠調用mStatusBar.updateNotification（）。

6. StatusBarManagerService 中mStatusBar.updateNotification()方法

  public void updateNotification(IBinder key, StatusBarNotification notification) {
512        synchronized (mNotifications) {
516            mNotifications.put(key, notification);
......
519                    mBar.updateNotification(key, notification);
......
524    }

這裡會調用mBar.updateNotification(),mBar是什麼？

7. StatusBarManagerService 中 mBar對象

volatile IStatusBar mBar;

  // Callbacks from the status bar service.
428    // ================================================================================
429    public void registerStatusBar(IStatusBar bar, StatusBarIconList iconList,
430            List notificationKeys, List notifications,
431            int switches[], List binders) {
......  

上面發現有個registerStatusBar方法，會傳遞進來一個IStatusBar 對象，那這個方法會在哪裡調用呢？

8. 在StatusBarManagerService中，我們發現調用mBar對象都是去處理StatusBar的UI，那這個StatusBar是哪裡的？SystemUI裡面的。檢索下SystemUI的代碼，果然發現在

BaseStatusBar裡面：

 public void start() { 
mBarService.registerStatusBar(mCommandQueue, iconList, notificationKeys, notifications,
250                    switches, binders);
}

在這裡registerStatusBar, 而這個mCommandQueue參數就是前面IStatusBar對象。

9. mCommanQueue變量

 protected CommandQueue mCommandQueue;

28/**
29 * This class takes the functions from IStatusBar that come in on
30 * binder pool threads and posts messages to get them onto the main
31 * thread, and calls onto Callbacks.  It also takes care of
32 * coalescing these calls so they don't stack up.  For the calls
33 * are coalesced, note that they are all idempotent.
34 */
35public class CommandQueue extends IStatusBar.Stub{
/**
78     * These methods are called back on the main thread.
79     */
80    public interface Callbacks {
81        public void addIcon(String slot, int index, int viewIndex, StatusBarIcon icon);
82        public void updateIcon(String slot, int index, int viewIndex,
83                StatusBarIcon old, StatusBarIcon icon);
84        public void removeIcon(String slot, int index, int viewIndex);
85        public void addNotification(IBinder key, StatusBarNotification notification);
86        public void updateNotification(IBinder key, StatusBarNotification notification);
87        public void removeNotification(IBinder key);
88        public void disable(int state);
89        public void animateExpandNotificationsPanel();
90        public void animateCollapsePanels(int flags);
91        public void animateExpandSettingsPanel();
92        public void setSystemUiVisibility(int vis, int mask);
93        public void topAppWindowChanged(boolean visible);
94        public void setImeWindowStatus(IBinder token, int vis, int backDisposition);
95        public void setHardKeyboardStatus(boolean available, boolean enabled);
96        public void toggleRecentApps();
97        public void preloadRecentApps();
98        public void showSearchPanel();
99        public void hideSearchPanel();
100        public void cancelPreloadRecentApps();
101        public void setNavigationIconHints(int hints);
102        public void setWindowState(int window, int state);
103    }

}

發現這個方法繼承IStatusBar.stub,裡面有一連串的回調函數。這些回調函數在BaseStatusBar裡面實現的

public abstract class BaseStatusBar extends SystemUI implements
79        CommandQueue.Callbacks {

10. 回到第6步，當在StatusBarManagerService中調用mBar.updateNotification時，根據7，8，9的分析，最終會調用在BaseStatusBar裡面實現的UpdateNotification方法

 updateNotification(IBinder key, StatusBarNotification notification) {
......
}

在這裡會將Notification顯 示在StatusBar上面。

這裡面主要涉及到兩個NotificationManagerService和StatusBarManager的交互。

第一步。

系統啟動時在ServerThread裡生成StatusBarManagerService和NotificationManagerService，並將StatusBarManagerService對象作為一個參數傳遞到NotificationManagerService的構造方法中。

系統加載應用，SystemUI中， BaseStatusBar實現回調函數CommandQueue.Callbacks, 並調用StatusBarManagerService的registerStatusBar方法，將CommandQueue對象傳遞進去

第二步

Activity裡調用notify方法，在NotificationManagerService將Notification封裝成StatusBarNotification。

NotificationManagerService調用statusBarManagerService的updateNotification()。

第三步

StatusBarManagerService調用CommandQueue實現的回調函數，最終將Notification顯示在SystemUI上面。

下一篇文章會講怎麼實現捕獲Notification的內容，從而實現采集第三方播放器播放音樂的信息