1. SystemServer启动（main方法被调用）

public final class SystemServer {
    public static void main(String[] args) {
        new SystemServer().run();
    }
    private void run() {
        mSystemServiceManager = new SystemServiceManager(mSystemContext);
        mSystemServiceManager.startService(NotificationManagerService.class);
    }
}

1. NotificationManagerService启动（onStart方法被调用）

public class SystemServiceManager {
    public SystemService startService(String className) {
        1. 反射创建NotificationManagerService对象
        2. 调用NotificationManagerService#onStart()方法
    }
}

1. NotificationManagerService#onStart()初始化

public class NotificationManagerService extends SystemService {
    private final IBinder mService = new INotificationManager.Stub() {}
    @Override
    public void onStart() {
         1. 公布mService，添加到ServiceManager
    }
}

1. NotificationManager#getService()拿到INotificationManager对象

public class NotificationManager {
    private static INotificationManager sService
    static public INotificationManager getService() {
        if (sService != null) {
            return sService;
        }
        IBinder b = ServiceManager.getService("notification");
        sService = INotificationManager.Stub.asInterface(b);
        return sService;
    }
}

1. NotificationManager通过INotificationManager接口调用NotificationManagerService里的INotificationManager.Stub()对象

public class NotificationManagerService extends SystemService {
    private final IBinder mService = new INotificationManager.Stub() {
         1. 取消通知
         2. 获取当前通知
         3. 注册监听器NotificationListenerService#INotificationListener
         3. 取消监听器NotificationListenerService#INotificationListener
    }
}

1. NotificationListenerService 里封装了INotificationListener对象

NotificationListenerService extends Service {
    private INotificationListenerWrapper mWrapper = null;
    private class INotificationListenerWrapper extends INotificationListener.Stub {}
    1. 创建INotificationListenerWrapper对象
    2. 通过INotificationManager注册INotificationListener
}

1. 实现INotificationListener回调接口

oneway interface INotificationListener
{
    void onListenerConnected(in NotificationRankingUpdate update);
    void onNotificationPosted(in IStatusBarNotificationHolder notificationHolder,
            in NotificationRankingUpdate update);
    void onNotificationRemoved(in IStatusBarNotificationHolder notificationHolder,
            in NotificationRankingUpdate update);
    void onNotificationRankingUpdate(in NotificationRankingUpdate update);
    void onListenerHintsChanged(int hints);
    void onInterruptionFilterChanged(int interruptionFilter);
}