通知大致流程

NotificationManager.java    (framework)
    | notify()
    | notifyAsUser()
        | service.enqueueNotificationWithTag( , , , , fixNotification (), )
        
NotificationManagerService.java    (framework)
    | enqueueNotificationWithTag()
    | enqueueNotificationInternal()
    | enqueueNotificationInternal( , , )
    | enqueueNotificationInternal( , , , , )
        | fixNotification()
        | StatusBarNotification    // SystemUI 会用
        | NotificationChannel
        | NotificationRecord    // framework 用
        | checkDisqualifyingFeatures()
        | mHandler.post(new EnqueueNotificationRunnable(userId, r, isAppForeground, tracker));
        
    EnqueueNotificationRunnable implements Runnable
        | enqueueNotification()
        | PostNotificationRunnable
    
    PostNotificationRunnable
        | postNotification()
        | notifyListenersPostedAndLogLocked()
        | prepareNotifyPostedLocked() --> NotificationListeners#prepareNotifyPostedLocked()
        
        
        
        
        class NotificationListeners    (NotificationManagerService.java里)
                // notifyRemoved
                // This notification became invisible -> remove the old one.
                if (oldSbnVisible && !sbnVisible) {
                    final StatusBarNotification oldSbnLightClone = oldSbn.cloneLight();
                    listenerCalls.add(() -> notifyRemoved(
                            info, oldSbnLightClone, update, null, REASON_USER_STOPPED));
                    continue;
                }
                // notifyPosted 
                final StatusBarNotification sbnToPost = trimCache.ForListener(info);
                listenerCalls.add(() -> notifyPosted(info, sbnToPost, update));
                
                
            private void notifyPosted(final ManagedServiceInfo info,
                final StatusBarNotification sbn, NotificationRankingUpdate rankingUpdate) {
                final INotificationListener listener = (INotificationListener) info.service;
                StatusBarNotificationHolder sbnHolder = new StatusBarNotificationHolder(sbn);
                try {
                    listener.onNotificationPosted(sbnHolder, rankingUpdate);
                } catch (android.os.DeadObjectException ex) {
                    Slog.wtf(TAG, "unable to notify listener (posted): " + info, ex);
                } catch (RemoteException ex) {
                    Slog.e(TAG, "unable to notify listener (posted): " + info, ex);
                }
            }
                
NotificationListener.java  (SystemUI)
    onNotificationPosted()

interface NotificationHandler （是NotificationListener.java 内部接口）
    onNotificationPosted()