Android?NotificationListenerService?通知服務原理解析

更新時間：2022年11月18日 10:20:16 作者：黃林晴

這篇文章主要為大家介紹了Android?NotificationListenerService?通知服務原理解析，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進步，早日升職加薪

前言

在上一篇通知服務NotificationListenerService使用方法中，我們已經(jīng)介紹了如何使用NotificationListenerService來監(jiān)聽消息通知，在最后我們還模擬了如何實現(xiàn)微信自動搶紅包功能。

那么NotificationListenerService是如何實現(xiàn)系統(tǒng)通知監(jiān)聽的呢？（本篇源碼分析基于API 32）

NotificationListenerService方法集

NotificationLisenerService是Service的子類

public abstract class NotificationListenerService extends Service

除了Service的方法屬性外，NotificationListenerService還為我們提供了收到通知、通知被移除、連接到通知管理器等方法，如下圖所示。

一般業(yè)務中我們只關(guān)注有標簽的那四個方法即可。

NotificationListenerService接收流程

既然NotificationListenerService是繼承自Service的，我們先來看它的onBind方法，代碼如下所示。

@Override
public IBinder onBind(Intent intent) {
    if (mWrapper == null) {
        mWrapper = new NotificationListenerWrapper();
    }
    return mWrapper;
}

在onBind方法中返回了一個NotificationListenerWrapper實例，NotificationListenerWrapper對象是定義在NotificationListenerService中的一個內(nèi)部類。主要方法如下所示。

/** @hide */
protected class NotificationListenerWrapper extends INotificationListener.Stub {
    @Override
    public void onNotificationPosted(IStatusBarNotificationHolder sbnHolder,
            NotificationRankingUpdate update) {
        StatusBarNotification sbn;
        try {
            sbn = sbnHolder.get();
        } catch (RemoteException e) {
            Log.w(TAG, "onNotificationPosted: Error receiving StatusBarNotification", e);
            return;
        }
        if (sbn == null) {
            Log.w(TAG, "onNotificationPosted: Error receiving StatusBarNotification");
            return;
        }
        try {
            // convert icon metadata to legacy format for older clients
            createLegacyIconExtras(sbn.getNotification());
            maybePopulateRemoteViews(sbn.getNotification());
            maybePopulatePeople(sbn.getNotification());
        } catch (IllegalArgumentException e) {
            // warn and drop corrupt notification
            Log.w(TAG, "onNotificationPosted: can't rebuild notification from " +
                    sbn.getPackageName());
            sbn = null;
        }
        // protect subclass from concurrent modifications of (@link mNotificationKeys}.
        synchronized (mLock) {
            applyUpdateLocked(update);
            if (sbn != null) {
                SomeArgs args = SomeArgs.obtain();
                args.arg1 = sbn;
                args.arg2 = mRankingMap;
                mHandler.obtainMessage(MyHandler.MSG_ON_NOTIFICATION_POSTED,
                        args).sendToTarget();
            } else {
                // still pass along the ranking map, it may contain other information
                mHandler.obtainMessage(MyHandler.MSG_ON_NOTIFICATION_RANKING_UPDATE,
                        mRankingMap).sendToTarget();
            }
        }
        ...省略onNotificationRemoved等方法
    }

NotificationListenerWrapper繼承自INotificationListener.Stub，當我們看到Stub這一關(guān)鍵字的時候，就應該知道這里是使用AIDL實現(xiàn)了跨進程通信。

在NotificationListenerWrapper的onNotificationPosted中通過代碼

mHandler.obtainMessage(MyHandler.MSG_ON_NOTIFICATION_POSTED,
                        args).sendToTarget();

將消息發(fā)送出去，handler接受后，又調(diào)用NotificationListernerService的onNotificationPosted方法，進而實現(xiàn)通知消息的監(jiān)聽。代碼如下所示。

private final class MyHandler extends Handler {
        public static final int MSG_ON_NOTIFICATION_POSTED = 1;
        @Override
        public void handleMessage(Message msg) {
            if (!isConnected) {
                return;
            }
            switch (msg.what) {
                case MSG_ON_NOTIFICATION_POSTED: {
                    SomeArgs args = (SomeArgs) msg.obj;
                    StatusBarNotification sbn = (StatusBarNotification) args.arg1;
                    RankingMap rankingMap = (RankingMap) args.arg2;
                    args.recycle();
                    onNotificationPosted(sbn, rankingMap);
                } break;
           ...
            }
        }
    }

那么，消息通知發(fā)送時，又是如何與NotificationListenerWrapper通信的呢？

通知消息發(fā)送流程

當客戶端發(fā)送一個通知的時候，會調(diào)用如下所示的代碼

notificationManager.notify(1, notification)

notify又會調(diào)用notifyAsUser方法，代碼如下所示

public void notifyAsUser(String tag, int id, Notification notification, UserHandle user)
{
    INotificationManager service = getService();
    String pkg = mContext.getPackageName();
    try {
        if (localLOGV) Log.v(TAG, pkg + ": notify(" + id + ", " + notification + ")");
        service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id,
                fixNotification(notification), user.getIdentifier());
    } catch (RemoteException e) {
        throw e.rethrowFromSystemServer();
    }
}

緊接著又會走到INotificationManager的enqueueNotificationWithTag方法中，enqueueNotificationWithTag是聲明在INotificationManager.aidl文件中的接口

/** {@hide} */
interface INotificationManager
{
    @UnsupportedAppUsage
    void cancelAllNotifications(String pkg, int userId);
    ...
    void cancelToast(String pkg, IBinder token);
    void finishToken(String pkg, IBinder token);
    void enqueueNotificationWithTag(String pkg, String opPkg, String tag, int id,
            in Notification notification, int userId);
    ...
 }

這個接口是在NotificationManagerService中實現(xiàn)的，接著我們轉(zhuǎn)到NotificationManagerService中去查看，相關(guān)主要代碼如下所示。

@VisibleForTesting
final IBinder mService = new INotificationManager.Stub() {
  @Override
       public void enqueueNotificationWithTag(String pkg, String opPkg, String tag, int id,
                  Notification notification, int userId) throws RemoteException {
              enqueueNotificationInternal(pkg, opPkg, Binder.getCallingUid(),
                      Binder.getCallingPid(), tag, id, notification, userId);
         }
}

enqueueNotificationWithTag方法會走進enqueueNotificationInternal方法，在方法最后會通過Handler發(fā)送一個EnqueueNotificationRunnable，代碼如下所示。

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, boolean postSilently) {
        ...
        //構(gòu)造StatusBarNotification，用于分發(fā)監(jiān)聽服務
        final StatusBarNotification n = new StatusBarNotification(
                pkg, opPkg, id, tag, notificationUid, callingPid, notification,
                user, null, System.currentTimeMillis());
        // setup local book-keeping
        String channelId = notification.getChannelId();
        if (mIsTelevision && (new Notification.TvExtender(notification)).getChannelId() != null) {
            channelId = (new Notification.TvExtender(notification)).getChannelId();
        }
        ...
        // 設置intent的白名點，是否盛典、是否后臺啟動等
        if (notification.allPendingIntents != null) {
            final int intentCount = notification.allPendingIntents.size();
            if (intentCount > 0) {
                final long duration = LocalServices.getService(
                        DeviceIdleInternal.class).getNotificationAllowlistDuration();
                for (int i = 0; i < intentCount; i++) {
                    PendingIntent pendingIntent = notification.allPendingIntents.valueAt(i);
                    if (pendingIntent != null) {
                        mAmi.setPendingIntentAllowlistDuration(pendingIntent.getTarget(),
                                ALLOWLIST_TOKEN, duration,
                                TEMPORARY_ALLOWLIST_TYPE_FOREGROUND_SERVICE_ALLOWED,
                                REASON_NOTIFICATION_SERVICE,
                                "NotificationManagerService");
                        mAmi.setPendingIntentAllowBgActivityStarts(pendingIntent.getTarget(),
                                ALLOWLIST_TOKEN, (FLAG_ACTIVITY_SENDER | FLAG_BROADCAST_SENDER
                                        | FLAG_SERVICE_SENDER));
                    }
                }
            }
        }
        ...
        mHandler.post(new EnqueueNotificationRunnable(userId, r, isAppForeground));
    }

EnqueueNotificationRunnable源碼如下所示。

protected class EnqueueNotificationRunnable implements Runnable {
        private final NotificationRecord r;
        private final int userId;
        private final boolean isAppForeground;
        EnqueueNotificationRunnable(int userId, NotificationRecord r, boolean foreground) {
            this.userId = userId;
            this.r = r;
            this.isAppForeground = foreground;
        }
        @Override
        public void run() {
            synchronized (mNotificationLock) {
                ...
                //將通知加入隊列
                mEnqueuedNotifications.add(r);
                scheduleTimeoutLocked(r);
                ...
                if (mAssistants.isEnabled()) {
                    mAssistants.onNotificationEnqueuedLocked(r);
                    mHandler.postDelayed(new PostNotificationRunnable(r.getKey()),
                            DELAY_FOR_ASSISTANT_TIME);
                } else {
                    mHandler.post(new PostNotificationRunnable(r.getKey()));
                }
            }
        }
    }

在EnqueueNotificationRunnable最后又會發(fā)送一個PostNotificationRunable，

PostNotificationRunable源碼如下所示。

protected class PostNotificationRunnable implements Runnable {
        private final String key;
        PostNotificationRunnable(String key) {
            this.key = key;
        }
        @Override
        public void run() {
            synchronized (mNotificationLock) {
                try {
                    ...
                    //發(fā)送通知
                    if (notification.getSmallIcon() != null) {
                        StatusBarNotification oldSbn = (old != null) ? old.getSbn() : null;
                        mListeners.notifyPostedLocked(r, old);
                        if ((oldSbn == null || !Objects.equals(oldSbn.getGroup(), n.getGroup()))
                                && !isCritical(r)) {
                            mHandler.post(new Runnable() {
                                @Override
                                public void run() {
                                    mGroupHelper.onNotificationPosted(
                                            n, hasAutoGroupSummaryLocked(n));
                                }
                            });
                        } else if (oldSbn != null) {
                            final NotificationRecord finalRecord = r;
                            mHandler.post(() -> mGroupHelper.onNotificationUpdated(
                                    finalRecord.getSbn(), hasAutoGroupSummaryLocked(n)));
                        }
                    } else {
                        //...
                    }
                } finally {
                    ...
                }
            }
        }
    }

從代碼中可以看出，PostNotificationRunable類中會調(diào)用notifyPostedLocked方法，這里你可能會有疑問：這里分明判斷notification.getSmallIcon()是否為null，不為null時才會進入notifyPostedLocked方法。為什么這里直接默認了呢？這是因為在Android5.0中規(guī)定smallIcon不可為null，且NotificationListenerService僅適用于5.0以上，所以這里是必然會執(zhí)行到notifyPostedLocked方法的。

其方法源碼如下所示。

 private void notifyPostedLocked(NotificationRecord r, NotificationRecord old,
                boolean notifyAllListeners) {
            try {
                // Lazily initialized snapshots of the notification.
                StatusBarNotification sbn = r.getSbn();
                StatusBarNotification oldSbn = (old != null) ? old.getSbn() : null;
                TrimCache trimCache = new TrimCache(sbn);
                //循環(huán)通知每個ManagedServiceInfo對象
                for (final ManagedServiceInfo info : getServices()) {
                    ...
                    mHandler.post(() -> notifyPosted(info, sbnToPost, update));
                }
            } catch (Exception e) {
                Slog.e(TAG, "Could not notify listeners for " + r.getKey(), e);
            }
        }

notifyPostedLocked方法最終會調(diào)用notifyPosted方法，我們再來看notifyPosted方法。

 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 (RemoteException ex) {
                Slog.e(TAG, "unable to notify listener (posted): " + info, ex);
           }
 }

notifyPosted方法，最終會調(diào)用INotificationListerner的onNotificationPosted方法，這樣就通知到了NotificationListenerService的onNotificationPosted方法。

上述方法的流程圖如下圖所示。

NotificationListenerService注冊

在NotificationListenerService中通過registerAsSystemService方法注冊服務，代碼如下所示。

 @SystemApi
    public void registerAsSystemService(Context context, ComponentName componentName,
            int currentUser) throws RemoteException {
        if (mWrapper == null) {
            mWrapper = new NotificationListenerWrapper();
        }
        mSystemContext = context;
        INotificationManager noMan = getNotificationInterface();
        mHandler = new MyHandler(context.getMainLooper());
        mCurrentUser = currentUser;
        noMan.registerListener(mWrapper, componentName, currentUser);
    }

registerAsSystemService方法將NotificationListenerWrapper對象注冊到NotificationManagerService中。如此就實現(xiàn)了對系統(tǒng)通知的監(jiān)聽。

總結(jié)

NotificationListenerService實現(xiàn)對系統(tǒng)通知的監(jiān)聽可以概括為三步：

NotificationListenerService將 NotificationListenerWrapper注冊到NotificationManagerService中。
當有通知被發(fā)送時，NotificationManagerService跨進程通知到每個NotificationListenerWrapper。
NotificationListenerWrapper中信息由NotificationListenerService類中的Handler中處理，從而調(diào)用NotificationListenerService中對應的回調(diào)方法。

以上就是Android NotificationListenerService 通知服務原理解析的詳細內(nèi)容，更多關(guān)于Android NotificationListenerService的資料請關(guān)注腳本之家其它相關(guān)文章！

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