前言

上一篇文章简单讲述了系统通知服务NotificationManagerService的启动流程，本篇文章我们将会具体梳理一下SystemUI组件系统状态栏StatusBar是如何监听通知服务的各种通知事件的。

一、StatusBar调用NotificationListener的setUpWithPresenter

1、我们在Android 9.0系统源码_SystemUI（一）SystemUI的启动流程系列文章有具体分析过SystemUI的启动流程，在状态栏StatusBar被创建之后，首先触发的便是start方法。

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/StatusBar.java

public class StatusBar extends SystemUI implements DemoMode,DragDownHelper.DragDownCallback, ActivityStarter, OnUnlockMethodChangedListener,OnHeadsUpChangedListener, CommandQueue.Callbacks, ZenModeController.Callback,ColorExtractor.OnColorsChangedListener, ConfigurationListener, NotificationPresenter {protected NotificationListener mNotificationListener;protected NotificationEntryManager mEntryManager;@Overridepublic void start() {...代码省略...mNotificationListener =  Dependency.get(NotificationListener.class);mEntryManager = Dependency.get(NotificationEntryManager.class);...代码省略...createAndAddWindows();//创建状态栏并添加到窗口上...代码省略...// Set up the initial notification state.//监听NotificationManagerService的通知消息mNotificationListener.setUpWithPresenter(this, mEntryManager);...代码省略...}}

在start方法中会获取NotificationListener实例对象，并调用该对象的setUpWithPresenter方法。

二、NotificationListener设置通知服务的回调方法。

1、NotificationListener的setUpWithPresenter方法如下所示。

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/NotificationListener.java

public class NotificationListener extends NotificationListenerWithPlugins {private static final String TAG = "NotificationListener";private final Context mContext;protected NotificationPresenter mPresenter;protected NotificationEntryManager mEntryManager;public NotificationListener(Context context) {mContext = context;}@Overridepublic void onListenerConnected() {...连接成功...}@Overridepublic void onNotificationPosted(final StatusBarNotification sbn,final RankingMap rankingMap) {...新的通知...}@Overridepublic void onNotificationRemoved(StatusBarNotification sbn,final RankingMap rankingMap) {...移除通知...}@Overridepublic void onNotificationRankingUpdate(final RankingMap rankingMap) {...更新通知...}public void setUpWithPresenter(NotificationPresenter presenter, NotificationEntryManager entryManager) {mPresenter = presenter;mEntryManager = entryManager;try {registerAsSystemService(mContext, new ComponentName(mContext.getPackageName(), getClass().getCanonicalName()), UserHandle.USER_ALL);} catch (RemoteException e) {Log.e(TAG, "Unable to register notification listener", e);}}
}

NotificationListener自身的各种回调方法会在特定情况下被通知服务所触发，而设置监听通知服务的setUpWithPresenter方法在给mPresenter和mEntryManager赋值之后，会进一步调用父类NotificationListenerWithPlugins的registerAsSystemService方法。

2、NotificationListenerWithPlugins的registerAsSystemService方法如下所示。

frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/phone/NotificationListenerWithPlugins.java

public class NotificationListenerWithPlugins extends NotificationListenerService implementsPluginListener {@Overridepublic void registerAsSystemService(Context context, ComponentName componentName,int currentUser) throws RemoteException {super.registerAsSystemService(context, componentName, currentUser);Dependency.get(PluginManager.class).addPluginListener(this, NotificationListenerController.class);}
}

3、NotificationListenerWithPlugins会继续调用自己的父类NotificationListenerService的registerAsSystemService方法。

frameworks/base/core/java/android/service/notification/NotificationListenerService.java

public abstract class NotificationListenerService extends Service {protected NotificationListenerWrapper mWrapper = null;protected Context mSystemContext;private Handler mHandler;protected int mCurrentUser;public void registerAsSystemService(Context context, ComponentName componentName,int currentUser) throws RemoteException {if (mWrapper == null) {// 这就是要注册的Binder，也就一个回调mWrapper = new NotificationListenerWrapper();}mSystemContext = context;INotificationManager noMan = getNotificationInterface();mHandler = new MyHandler(context.getMainLooper());mCurrentUser = currentUser;//向通知服务NotificationManagerService注册回调noMan.registerListener(mWrapper, componentName, currentUser);}//获取通知服务protected final INotificationManager getNotificationInterface() {if (mNoMan == null) {mNoMan = INotificationManager.Stub.asInterface(ServiceManager.getService(Context.NOTIFICATION_SERVICE));}return mNoMan;}//回调对象protected class NotificationListenerWrapper extends INotificationListener.Stub {@Overridepublic void onNotificationPosted(IStatusBarNotificationHolder sbnHolder,NotificationRankingUpdate update) {...有通知事件...}@Overridepublic void onListenerConnected(NotificationRankingUpdate update) {...连接成功...}}
}

NotificationListenerService的registerAsSystemService方法首先创建一个类型为NotificationListenerWrapper的mWrapper对象，NotificationListenerWrapper是NotificationListenerService的内部类，该类实现了INotificationListener.Stub，然后会调用getNotificationInterface方法，获取NotificationManagerService对象实例并调用registerListener方法。

5、NotificationManagerService的registerListener方法如下所示。

public class NotificationManagerService extends SystemService {private NotificationListeners mListeners;//主要用于管理通知的接收者void init(Looper looper, IPackageManager packageManager,PackageManager packageManagerClient,LightsManager lightsManager, NotificationListeners notificationListeners,NotificationAssistants notificationAssistants, ConditionProviders conditionProviders,ICompanionDeviceManager companionManager, SnoozeHelper snoozeHelper,NotificationUsageStats usageStats, AtomicFile policyFile,ActivityManager activityManager, GroupHelper groupHelper, IActivityManager am,UsageStatsManagerInternal appUsageStats, DevicePolicyManagerInternal dpm) {...代码省略...// This is a ManagedServices object that keeps track of the listeners.mListeners = notificationListeners;...代码省略...}@Overridepublic void registerListener(final INotificationListener listener,final ComponentName component, final int userid) {enforceSystemOrSystemUI("INotificationManager.registerListener");mListeners.registerService(listener, component, userid);}
}

这里的mListeners，其实就是NotificationManagerService的init方法中提到类型为NotificationListeners的mListeners。

6、NotificationListeners是NotificationManagerService的内部类。

public class NotificationManagerService extends SystemService {public class NotificationListeners extends ManagedServices {private final ArraySet mLightTrimListeners = new ArraySet<>();public NotificationListeners(IPackageManager pm) {super(getContext(), mNotificationLock, mUserProfiles, pm);}}
}

7、我们在NotificationListeners类中并不能找到registerService方法，这是因为该方法定义在他的父类ManagedServices中。

frameworks/base/services/core/java/com/android/server/notification/ManagedServices.java

abstract public class ManagedServices {public void registerService(IInterface service, ComponentName component, int userid) {checkNotNull(service);//继续调用registerServiceImplManagedServiceInfo info = registerServiceImpl(service, component, userid);if (info != null) {onServiceAdded(info);}}private ManagedServiceInfo registerServiceImpl(final IInterface service,final ComponentName component, final int userid) {//调用newServiceInfo方法创建ManagedServiceInfo对象实例ManagedServiceInfo info = newServiceInfo(service, component, userid,true /*isSystem*/, null /*connection*/, Build.VERSION_CODES.LOLLIPOP);//将新创建的ManagedServiceInfo作为参数继续调用registerServiceImpl方法。return registerServiceImpl(info);}private ManagedServiceInfo newServiceInfo(IInterface service,ComponentName component, int userId, boolean isSystem, ServiceConnection connection,int targetSdkVersion) {//创建ManagedServiceInfo对象实例return new ManagedServiceInfo(service, component, userId, isSystem, connection,targetSdkVersion);}|

8、ManagedServiceInfo 是 ManagedServices 的内部类。

abstract public class ManagedServices {public class ManagedServiceInfo implements IBinder.DeathRecipient {public IInterface service;//指向的就是前面提到的NotificationListenerWrapper对象，是一个代理对象public ComponentName component;public int userid;public boolean isSystem;public ServiceConnection connection;public int targetSdkVersion;public ManagedServiceInfo(IInterface service, ComponentName component,int userid, boolean isSystem, ServiceConnection connection, int targetSdkVersion) {this.service = service;this.component = component;this.userid = userid;this.isSystem = isSystem;this.connection = connection;this.targetSdkVersion = targetSdkVersion;}}}       

结合ManagedServiceInfo的构造方法可知，最终时将前面提到的NotificationListenerWrapper对象赋值给了类型为IInterface的变量service，NotificationListenerWrapper是一个代理对象，该对象运行在SystemUI进程中用于接收系统通知。

9、在ManagedServiceInfo 对象创建完毕之后，会继续调用registerServiceImpl方法。

abstract public class ManagedServices {private final ArrayList mServices = new ArrayList<>();private ManagedServiceInfo registerServiceImpl(ManagedServiceInfo info) {synchronized (mMutex) {try {info.service.asBinder().linkToDeath(info, 0);mServices.add(info);return info;} catch (RemoteException e) {// already dead}}return null;}
}    

由上可知最终将ManagedServiceInfo实例对象存储在了类型为集合mServices中。

10、重新回到前面第7步，在创建完ManagedServiceInfo对象之后，如果创建的ManagedServiceInfo实例对象不为空，则会调用onServiceAdded方法。

abstract public class ManagedServices {private final ArrayList mServices = new ArrayList<>();public void registerService(IInterface service, ComponentName component, int userid) {checkNotNull(service);//继续调用registerServiceImplManagedServiceInfo info = registerServiceImpl(service, component, userid);if (info != null) {onServiceAdded(info);}}abstract protected void onServiceAdded(ManagedServiceInfo info); }

11、onServiceAdded方法是一个抽象方法，具体实现是在前面提到的NotificationManagerService的内部类NotificationListeners中。

public class NotificationManagerService extends SystemService {public class NotificationListeners extends ManagedServices {@Overridepublic void onServiceAdded(ManagedServiceInfo info) {final INotificationListener listener = (INotificationListener) info.service;final NotificationRankingUpdate update;synchronized (mNotificationLock) {update = makeRankingUpdateLocked(info);}try {//注册成功，开始进行回调通知listener.onListenerConnected(update);} catch (RemoteException e) {// we tried}}}
}

绕了这么一大圈，总算是触发INotificationListener的onListenerConnected回调方法了，而INotificationListener的具体实现者我们前面有提到，就是NotificationListenerService的内部类NotificationListenerWrapper。

三、NotificationListener设置回调方法被触发。

1、NotificationListenerService$NotificationListenerWrapper类中和onListenerConnected回调方法相关的代码如下所示。

public abstract class NotificationListenerService extends Service {private Handler mHandler;@Overrideprotected void attachBaseContext(Context base) {super.attachBaseContext(base);mHandler = new MyHandler(getMainLooper());}private final class MyHandler extends Handler {public static final int MSG_ON_LISTENER_CONNECTED = 3;public MyHandler(Looper looper) {super(looper, null, false);}@Overridepublic void handleMessage(Message msg) {if (!isConnected) {return;}switch (msg.what) {...代码省略...case MSG_ON_LISTENER_CONNECTED: {//回调会NotificationListenerService的onListenerConnected方法。onListenerConnected();} break;...代码省略...}}public void onListenerConnected() {...连接成功...}//回调对象protected class NotificationListenerWrapper extends INotificationListener.Stub {@Overridepublic void onNotificationPosted(IStatusBarNotificationHolder sbnHolder,NotificationRankingUpdate update) {...有通知事件...}//和通知服务建立连接成功@Overridepublic void onListenerConnected(NotificationRankingUpdate update) {// protect subclass from concurrent modifications of (@link mNotificationKeys}.Log.d("NotificationListenerService","onListenerConnected exec");synchronized (mLock) {applyUpdateLocked(update);}isConnected = true;//发送消息，触发MyHandler的handleMessage方法。mHandler.obtainMessage(MyHandler.MSG_ON_LISTENER_CONNECTED).sendToTarget();}}
}

NotificationListenerService$NotificationListenerWrapper的onListenerConnected方法会调用mHandler发送类型为MSG_ON_LISTENER_CONNECTED的消息，该消息会触发MyHandler的handleMessage方法，最终触发NotificationListenerService 类的onListenerConnected方法。由于NotificationListener就是继承自NotificationListenerService的，并且它还重写了onListenerConnected方法，这样回调就来到了它这边。

2、当通知服务NotificationManangerService收到其他的各种通知事件的时候，NotificationListenerWrapper的各个回调方法便会被触发，然后通过类型为MyHandler的mHandler发送对应的消息，进一步触发NotificationListenerService所对应的回调方法，也就是NotificationListener的回调方法。

public class NotificationListener extends NotificationListenerWithPlugins {private static final String TAG = "NotificationListener";private final Context mContext;protected NotificationPresenter mPresenter;protected NotificationEntryManager mEntryManager;public NotificationListener(Context context) {mContext = context;}@Overridepublic void onListenerConnected() {...连接成功...}@Overridepublic void onNotificationPosted(final StatusBarNotification sbn,final RankingMap rankingMap) {if (sbn != null && !onPluginNotificationPosted(sbn, rankingMap)) {// 在主线程中进行更新mPresenter.getHandler().post(() -> {processForRemoteInput(sbn.getNotification(), mContext);String key = sbn.getKey();mEntryManager.removeKeyKeptForRemoteInput(key);boolean isUpdate = mEntryManager.getNotificationData().get(key) != null;// In case we don't allow child notifications, we ignore children of// notifications that have a summary, since` we're not going to show them// anyway. This is true also when the summary is canceled,// because children are automatically canceled by NoMan in that case.if (!ENABLE_CHILD_NOTIFICATIONS&& mPresenter.getGroupManager().isChildInGroupWithSummary(sbn)) {if (DEBUG) {Log.d(TAG, "Ignoring group child due to existing summary: " + sbn);}// Remove existing notification to avoid stale data.if (isUpdate) {mEntryManager.removeNotification(key, rankingMap);} else {mEntryManager.getNotificationData().updateRanking(rankingMap);}return;}//判断到来的通知是需要更新还是添加if (isUpdate) {// 更新通知操作mEntryManager.updateNotification(sbn, rankingMap);} else {// 添加新通知操作mEntryManager.addNotification(sbn, rankingMap);}});}}@Overridepublic void onNotificationRemoved(StatusBarNotification sbn,final RankingMap rankingMap) {...移除通知...}@Overridepublic void onNotificationRankingUpdate(final RankingMap rankingMap) {...更新通知...}public void setUpWithPresenter(NotificationPresenter presenter, NotificationEntryManager entryManager) {mPresenter = presenter;mEntryManager = entryManager;try {registerAsSystemService(mContext, new ComponentName(mContext.getPackageName(), getClass().getCanonicalName()), UserHandle.USER_ALL);} catch (RemoteException e) {Log.e(TAG, "Unable to register notification listener", e);}}
}

四、总结