Android 8.0 Notification 源码分析（一）

最近在搞SystemUI。这几天把Notification的流程整理了一遍。好记性不如烂博客。

本编主要介绍的为Notification从App产生到System中的流程。

另外一编讲诉的为SystemUI中怎样展示Notification

《Android O 8.0 Notification 源码分析（二）》。

值得注意的是在AndroidO 8.0中，notification有了改变，使用NotificationChannel类。具体使用参加下面的demo.

下面直接上流程图。

App->System Notification流程

上图为Apps产生Notification怎么发送到系统的中的流程图。

下面看代码：

步骤1，2，3，4 : MainActivity生产Notification准备工作。

    @RequiresApi(api = Build.VERSION_CODES.O)
    public void sendNotification(View view) {
        String id = "channel_0";
        String des = "111";
        NotificationChannel channel = new NotificationChannel(id, des, NotificationManager.IMPORTANCE_MIN);
        notificationManager.createNotificationChannel(channel);
        Notification notification = new Notification.Builder(MainActivity.this, id)
                .setContentTitle("Base Notification View")
                .setContentText("您有一条新通知")
                .setSmallIcon(R.drawable.jd_icon)
                .setStyle(new Notification.MediaStyle())
                .setAutoCancel(false)
                .build();
        notificationManager.notify(1, notification);
    }

步骤5，6: NotificationManager发送notification。最后调用到notifyAsUser()方法：

    public void notifyAsUser(String tag, int id, Notification notification, UserHandle user)
    {
        // 获取NotificationManager的Service
        INotificationManager service = getService();
        String pkg = mContext.getPackageName();
        ...
        notification.reduceImageSizes(mContext);
        ActivityManager am = (ActivityManager) mContext.getSystemService(Context.ACTIVITY_SERVICE);
        boolean isLowRam = am.isLowRamDevice();
        final Notification copy = Builder.maybeCloneStrippedForDelivery(notification, isLowRam);
        try {
            service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id, copy, user.getIdentifier());
        } catch (RemoteException e) {
            throw e.rethrowFromSystemServer();
        }
    }

步骤7,8,9,10: 根据Android的规律，INotificationManager对应的service为NotificationManagerService.最后直接enqueueNotificationInternal()方法。

void enqueueNotificationInternal(final String pkg, final String opPkg, final int callingUid, final int callingPid, final String tag, final int id, final Notification notification, int incomingUserId) {
        if (DBG) {
            Slog.v(TAG, "enqueueNotificationInternal: pkg=" + pkg + " id=" + id
                    + " notification=" + notification);
        }
        checkCallerIsSystemOrSameApp(pkg);
 
        ...
 
        final StatusBarNotification n = new StatusBarNotification(
                pkg, opPkg, id, tag, notificationUid, callingPid, notification,
                user, null, System.currentTimeMillis());
        // 把notification的对象做了备份
        final NotificationRecord r = new NotificationRecord(getContext(), n, channel);
 
        if ((notification.flags & Notification.FLAG_FOREGROUND_SERVICE) != 0
                && (channel.getUserLockedFields() & NotificationChannel.USER_LOCKED_IMPORTANCE) == 0
                && (r.getImportance() == IMPORTANCE_MIN || r.getImportance() == IMPORTANCE_NONE)) {
            // Increase the importance of foreground service notifications unless the user had an
            // opinion otherwise
            if (TextUtils.isEmpty(channelId)
                    || NotificationChannel.DEFAULT_CHANNEL_ID.equals(channelId)) {
                r.setImportance(IMPORTANCE_LOW, "Bumped for foreground service");
            } else {
                channel.setImportance(IMPORTANCE_LOW);
                mRankingHelper.updateNotificationChannel(pkg, notificationUid, channel, false);
                r.updateNotificationChannel(channel);
            }
        }
 
        if (!checkDisqualifyingFeatures(userId, notificationUid, id, tag, r,
                r.sbn.getOverrideGroupKey() != null)) {
            return;
        }
 
        // Whitelist pending intents.
        if (notification.allPendingIntents != null) {
            final int intentCount = notification.allPendingIntents.size();
            if (intentCount > 0) {
                final ActivityManagerInternal am = LocalServices
                        .getService(ActivityManagerInternal.class);
                final long duration = LocalServices.getService(
                        DeviceIdleController.LocalService.class).getNotificationWhitelistDuration();
                for (int i = 0; i < intentCount; i++) {
                    PendingIntent pendingIntent = notification.allPendingIntents.valueAt(i);
                    if (pendingIntent != null) {
                        am.setPendingIntentWhitelistDuration(pendingIntent.getTarget(),
                                WHITELIST_TOKEN, duration);
                    }
                }
            }
        }
 
        mHandler.post(new EnqueueNotificationRunnable(userId, r));
    }

步骤11：handler.post( EnqueueNotificationRunnable run)：

@Override
        public void run() {
            synchronized (mNotificationLock) {
                mEnqueuedNotifications.add(r);
                scheduleTimeoutLocked(r);
 
                final StatusBarNotification n = r.sbn;
                ...
 
                // tell the assistant service about the notification
                if (mAssistants.isEnabled()) {
                    mAssistants.onNotificationEnqueued(r);
                    mHandler.postDelayed(new PostNotificationRunnable(r.getKey()),
                            DELAY_FOR_ASSISTANT_TIME);
                } else {
                    mHandler.post(new PostNotificationRunnable(r.getKey()));
                }
            }
        }

步骤12,13:handler.post( PostNotificationRunnable run)：

@Override
        public void run() {
            synchronized (mNotificationLock) {
                try {
                    NotificationRecord r = null;
                    int N = mEnqueuedNotifications.size();
                    for (int i = 0; i < N; i++) {
                        final NotificationRecord enqueued = mEnqueuedNotifications.get(i);
                        if (Objects.equals(key, enqueued.getKey())) {
                            r = enqueued;
                            break;
                        }
                    }
                    ...
                    mNotificationsByKey.put(n.getKey(), r);
                    ...
                    //没有SmallIcon会失败
                    if (notification.getSmallIcon() != null) {
                        StatusBarNotification oldSbn = (old != null) ? old.sbn : null;
                        mListeners.notifyPostedLocked(n, oldSbn);
                        ...
                    } else {
                        Slog.e(TAG, "Not posting notification without small icon: " + notification);
                        ...
                    }
 
                    buzzBeepBlinkLocked(r);
                } finally {
                    int N = mEnqueuedNotifications.size();
                    for (int i = 0; i < N; i++) {
                        final NotificationRecord enqueued = mEnqueuedNotifications.get(i);
                        if (Objects.equals(key, enqueued.getKey())) {
                            mEnqueuedNotifications.remove(i);
                            break;
                        }
                    }
                }
            }
        }

步骤14：调用NotificationManagerService.NotificationListeners --> notifyPostedLocked() --> notifyPosted() --> NotificationListenerService.onNotificationPosted();

OK，上面描述了Notification从App应用，产生到系统的流程。

另外一编讲诉的为SystemUI中怎样展示Notification

《Android O 8.0 Notification 源码分析（二）》。