基于Android 7.0源码分析通知机制，相关源码如下：
frameworks/base/services/core/java/com/android/server/notification/
- NotificationManagerService.java
- ManagedServices.java
frameworks/base/core/java/android/app/
- NotificationManager.java
- Notification.java
frameworks/base/core/java/android/service/notification/
- NotificationListenerService.java
- StatusBarNotification.java
frameworks/base/packages/SystemUI/src/com/android/systemui/statusbar/
- phone/PhoneStatusBar.java
- BaseStatusBar.java
一. 概述
Android应用除了组件和窗口管理，还有通知显示也是非常重要的，通知是应用界面之外向用户显示的界面。 NotificationListenerService继承于Service，该服务是为了给app提供获取通知的新增和删除事件，通知的数量和内容等相关信息的途径，该类的主要方法：
- cancelAllNotifications() ：删除系统所有可被清除的通知；
- cancelNotification(String pkg, String tag, int id) ：删除某一个通知；
- onNotificationPosted(StatusBarNotification sbn) ：当系统收到新通知后触发回调方法；
- onNotificationRemoved(StatusBarNotification sbn) ：当系统通知被删掉后触发回调方法；
- getActiveNotifications() ：获取当前系统所有通知到StatusBarNotification[]；
1.1 通知使用实例
1.1.1 创建通知
PendingIntent targetIntent = PendingIntent.getActivity(
this, 0, new Intent(this, TargetActivity.class), 0);
Notification notification = new Notification.Builder(this)
.setSmallIcon(R.drawable.notification_icon) //小图标
.setContentTitle("Gityuan notification") //通知标题
.setContentText("Hello Gityuan") //通知内容
.setContentIntent(targetIntent) //目标Intent
.setAutoCancel(true) //自动取消
.build();
常见的Flags:
- FLAG_AUTO_CANCEL，当通知被用户点击之后会自动被清除(cancel)
- FLAG_INSISTENT，在用户响应之前会一直重复提醒音
- FLAG_ONGOING_EVENT，表示正在运行的事件
- FLAG_NO_CLEAR，通知栏点击“清除”按钮时，该通知将不会被清除
- FLAG_FOREGROUND_SERVICE，表示当前服务是前台服务
关于前台服务是用户可感知的，前台服务需要显示一个通知，比如后台播放音乐。
startForeground(ID, notification)//启动前台服务通知
stopForeground(true); //true表示移除之前的通知
1.1.2 发送通知
NotificationManager mNotificationManager =
(NotificationManager) context.getSystemService(NOTIFICATION_SERVICE);
mNotificationManager.notify(notifyID, notification);
创建通知过程，此处的PendingIntent是当通知被点击后的跳转动作，可以是启动Activity、Service，或者发送Broadcast。 对于更新通知只需要发送notifyID相同的通知即可。
1.1.3 取消通知
NotificationManager mNotificationManager =
(NotificationManager) context.getSystemService(NOTIFICATION_SERVICE);
mNotificationManager.cancel(notifyId); //取消指定ID的通知
mNotificationManager.cancelAll(); //取消所有通知
除了调用NotificationManager的cancel()或者cancelAll()，也可
- 点击通知栏的清除按钮，则会清除所有的可清除通知；
- 设置setAutoCancel()或FLAG_AUTO_CANCEL的通知，当点击该通知则会清除它。
1.2 架构图
1.2.1 核心类图
1.2.2 通知处理流程图
可见，通知发送与通知取消流程的步骤一直对齐，这里就只介绍通知发送流程，通知取消流程就不再介绍。
二. 通知发送原理分析
2.1 NM.notify
[-> NotificationManager.java]
public void notify(int id, Notification notification)
{
notify(null, id, notification);
}
public void notify(String tag, int id, Notification notification)
{
notifyAsUser(tag, id, notification, new UserHandle(UserHandle.myUserId()));
}
public void notifyAsUser(String tag, int id, Notification notification, UserHandle user)
{
int[] idOut = new int[1];
//获取通知的代理对象
INotificationManager service = getService();
String pkg = mContext.getPackageName();
//将包名和userId保存到通知的extras
Notification.addFieldsFromContext(mContext, notification);
...
fixLegacySmallIcon(notification, pkg);
//对于Android 5.0之后的版本，smallIcon不可为空
if (mContext.getApplicationInfo().targetSdkVersion > Build.VERSION_CODES.LOLLIPOP_MR1) {
if (notification.getSmallIcon() == null) {
throw new IllegalArgumentException(...);
}
}
final Notification copy = Builder.maybeCloneStrippedForDelivery(notification);
try {
//binder调用，进入system_server进程【2.2】
service.enqueueNotificationWithTag(pkg, mContext.getOpPackageName(), tag, id,
copy, idOut, user.getIdentifier());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
在App端调用NotificationManager类的notify()方法，最终通过binder调用，会进入system_server进程的 NotificationManagerService(简称NMS)，执行enqueueNotificationWithTag()方法。
2.2 NMS.enqueueNotificationInternal
[-> NotificationManagerService.java]
void enqueueNotificationInternal(final String pkg, final String opPkg, final int callingUid,
final int callingPid, final String tag, final int id, final Notification notification,
int[] idOut, int incomingUserId) {
//检查发起者是系统进程或者同一个app，否则抛出异常
checkCallerIsSystemOrSameApp(pkg);
final boolean isSystemNotification = isUidSystem(callingUid) || ("android".equals(pkg));
final boolean isNotificationFromListener = mListeners.isListenerPackage(pkg);
//除了系统通知和已注册的监听器允许入队列，其他通知都会限制数量上限，默认是一个package上限50个
...
//将通知信息封装到StatusBarNotification对象
final StatusBarNotification n = new StatusBarNotification(
pkg, opPkg, id, tag, callingUid, callingPid, 0, notification, user);
//创建记录通知实体的对象NotificationRecord
final NotificationRecord r = new NotificationRecord(getContext(), n);
//将通知异步发送到handler线程【见小节2.3】
mHandler.post(new EnqueueNotificationRunnable(userId, r));
}
这个过程主要功能：
- 创建NotificationRecord对象，里面包含了notification相关信息
- 采用异步方式，将任务交给mHandler线程来处理，mHandler是WorkerHandler类的实例对象
接下来看看WorkerHandler到底运行在哪个线程，这需要从NMS服务初始化过程来说起：
2.2.1 SS.startOtherServices
[-> SystemServer.java]
private void startOtherServices() {
//【见小节2.2.2】
mSystemServiceManager.startService(NotificationManagerService.class);
...
}
该过程运行在system_server进程的主线程。
2.2.2 SSM.startService
[-> SystemServiceManager.java]
public <T extends SystemService> T startService(Class<T> serviceClass) {
final String name = serviceClass.getName();
Constructor<T> constructor = serviceClass.getConstructor(Context.class);
//创建NotificationManagerService对象
final T service = constructor.newInstance(mContext);
//注册该服务
mServices.add(service);
//调用NMS的onStart方法，【见小节2.2.3】
service.onStart();
return service;
}
该过程先创建NotificationManagerService(简称NMS)，然后再调用其onStart方法。
2.2.3 NMS.onStart
[-> NMS.java]
public void onStart() {
...
mHandler = new WorkerHandler(); //运行在system_server的主线程
mRankingThread.start(); //线程名为"ranker"的handler线程
mRankingHandler = new RankingHandlerWorker(mRankingThread.getLooper());
...
//用于记录所有的listeners的MangedServices对象
mListeners = new NotificationListeners();
...
publishBinderService(Context.NOTIFICATION_SERVICE, mService);
publishLocalService(NotificationManagerInternal.class, mInternalService);
}
到此，我们可以得知onStart()过程创建的mHandler运行在system_server的主线程。那么上面的执行流便进入了 system_server主线程。
2.3 EnqueueNotificationRunnable
[-> NMS.java]
private class EnqueueNotificationRunnable implements Runnable {
public void run() {
synchronized (mNotificationList) {
//此处r为NotificationRecord对象
final StatusBarNotification n = r.sbn;
final Notification notification = n.getNotification();
...
//从通知列表mNotificationList查看是否存在该通知
int index = indexOfNotificationLocked(n.getKey());
if (index < 0) {
mNotificationList.add(r);
mUsageStats.registerPostedByApp(r);
} else {
old = mNotificationList.get(index);
mNotificationList.set(index, r);
mUsageStats.registerUpdatedByApp(r, old);
//确保通知的前台服务属性不会被丢弃
notification.flags |=
old.getNotification().flags & Notification.FLAG_FOREGROUND_SERVICE;
r.isUpdate = true;
}
mNotificationsByKey.put(n.getKey(), r);
//如果是前台服务的通知，则添加不允许被清除和正在运行的标签
if ((notification.flags & Notification.FLAG_FOREGROUND_SERVICE) != 0) {
notification.flags |= Notification.FLAG_ONGOING_EVENT
| Notification.FLAG_NO_CLEAR;
}
applyZenModeLocked(r);
mRankingHelper.sort(mNotificationList);
if (notification.getSmallIcon() != null) {
StatusBarNotification oldSbn = (old != null) ? old.sbn : null;
//当设置小图标，则通知NotificationListeners处理 【2.4】
mListeners.notifyPostedLocked(n, oldSbn);
} else {
if (old != null && !old.isCanceled) {
mListeners.notifyRemovedLocked(n);
}
}
//处理该通知，主要是是否发声，震动，Led灯
buzzBeepBlinkLocked(r);
}
}
}
这里的mListeners是指NotificationListeners对象
2.4 NotificationListeners.notifyPostedLocked
[-> NMS.java]
public class NotificationListeners extends ManagedServices {
public void notifyPostedLocked(StatusBarNotification sbn, StatusBarNotification oldSbn) {
TrimCache trimCache = new TrimCache(sbn);
//遍历整个ManagedServices中的所有ManagedServiceInfo
for (final ManagedServiceInfo info : mServices) {
boolean sbnVisible = isVisibleToListener(sbn, info);
boolean oldSbnVisible = oldSbn != null ? isVisibleToListener(oldSbn, info) : false;
if (!oldSbnVisible && !sbnVisible) {
continue;
}
final NotificationRankingUpdate update = makeRankingUpdateLocked(info);
//通知变得不可见，则移除老的通知
if (oldSbnVisible && !sbnVisible) {
final StatusBarNotification oldSbnLightClone = oldSbn.cloneLight();
mHandler.post(new Runnable() {
public void run() {
notifyRemoved(info, oldSbnLightClone, update);
}
});
continue;
}
final StatusBarNotification sbnToPost = trimCache.ForListener(info);
mHandler.post(new Runnable() {
public void run() {
notifyPosted(info, sbnToPost, update); //【见小节2.5】
}
});
}
}
...
}
这里是在system_server进程中第二次采用异步方式来处理。
2.5 NMS.notifyPosted
private void notifyPosted(final ManagedServiceInfo info,
final StatusBarNotification sbn, NotificationRankingUpdate rankingUpdate) {
final INotificationListener listener = (INotificationListener)info.service;
StatusBarNotificationHolder sbnHolder = new StatusBarNotificationHolder(sbn);
try {
// 【见小节2.6】
listener.onNotificationPosted(sbnHolder, rankingUpdate);
} catch (RemoteException ex) {
...
}
}
此处的listener来自于ManagedServiceInfo的service成员变量，listener数据类型是NotificationListenerWrapper的代理对象，详见第三大节。 此处sbnHolder的数据类型为StatusBarNotificationHolder，继承于IStatusBarNotificationHolder.Stub对象，经过binder调用进入到systemui进程的 便是IStatusBarNotificationHolder.Stub.Proxy对象。
2.6 NotificationListenerWrapper.onNotificationPosted
[-> NotificationListenerService.java]
protected class NotificationListenerWrapper extends INotificationListener.Stub {
public void onNotificationPosted(IStatusBarNotificationHolder sbnHolder,
NotificationRankingUpdate update) {
StatusBarNotification sbn;
try {
sbn = sbnHolder.get(); //向system_server进程来获取sbn对象
} catch (RemoteException e) {
return;
}
synchronized (mLock) {
applyUpdateLocked(update);
if (sbn != null) {
SomeArgs args = SomeArgs.obtain();
args.arg1 = sbn;
args.arg2 = mRankingMap;
//【2.7】
mHandler.obtainMessage(MyHandler.MSG_ON_NOTIFICATION_POSTED,
args).sendToTarget();
} else {
mHandler.obtainMessage(MyHandler.MSG_ON_NOTIFICATION_RANKING_UPDATE,
mRankingMap).sendToTarget();
}
}
}
...
}
此时运行在systemui进程，sbnHolder是IStatusBarNotificationHolder的代理端。 此处mHandler = new MyHandler(getMainLooper())，也就是运行在systemui主线程的handler
2.7 MyHandler
[-> NotificationListenerService.java]
private final class MyHandler extends Handler {
...
public void handleMessage(Message msg) {
...
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;
case ...
}
}
}
此处调用NotificationListenerService实例对象的onNotificationPosted()
2.8 NLS.onNotificationPosted
[-> BaseStatusBar.java]
private final NotificationListenerService mNotificationListener =
new NotificationListenerService() {
public void onNotificationPosted(final StatusBarNotification sbn,
final RankingMap rankingMap) {
if (sbn != null) {
mHandler.post(new Runnable() {
public void run() {
...
String key = sbn.getKey();
boolean isUpdate = mNotificationData.get(key) != null;
if (isUpdate) {
updateNotification(sbn, rankingMap);
} else {
//【2.9】
addNotification(sbn, rankingMap, null );
}
}
});
}
}
}
此处的mHandler便是systemui的主线程
2.9 addNotification
[-> PhoneStatusBar.java]
public void addNotification(StatusBarNotification notification, RankingMap ranking,
Entry oldEntry) {
mNotificationData.updateRanking(ranking); //更新排序
//创建通知视图【2.9.1】
Entry shadeEntry = createNotificationViews(notification);
if (shadeEntry == null) {
return;
}
...
//添加到通知栏
addNotificationViews(shadeEntry, ranking);
setAreThereNotifications();
}
如果创建的通知视图为空则会直接返回。
2.9.1 createNotificationViews
[-> BaseStatusBar.java]
protected NotificationData.Entry createNotificationViews(StatusBarNotification sbn) {
final StatusBarIconView iconView = createIcon(sbn);
if (iconView == null) {
return null;
}
NotificationData.Entry entry = new NotificationData.Entry(sbn, iconView);
if (!inflateViews(entry, mStackScroller)) {
return null;
}
return entry;
}
三. SystemUI
3.1 startOtherServices
[-> SystemServer.java]
private void startOtherServices() {
startSystemUi(context);
...
}
3.2 startSystemUi
[-> SystemServer.java]
static final void startSystemUi(Context context) {
Intent intent = new Intent();
intent.setComponent(new ComponentName("com.android.systemui",
"com.android.systemui.SystemUIService"));
intent.addFlags(Intent.FLAG_DEBUG_TRIAGED_MISSING);
//【见3.3】
context.startServiceAsUser(intent, UserHandle.SYSTEM);
}
启动服务SystemUIService，运行在进程com.android.systemui，接下来进入systemui进程
3.3 SystemUIService
[-> SystemUIService.java]
public class SystemUIService extends Service {
public void onCreate() {
super.onCreate();
//【见小节3.4】
((SystemUIApplication) getApplication()).startServicesIfNeeded();
}
...
}
服务启动后，先执行其onCreate()方法
3.4 startServicesIfNeeded
[-> SystemUIApplication.java]
public void startServicesIfNeeded() {
startServicesIfNeeded(SERVICES); //【见小节3.5】
}
//SERVICES常量值
private final Class<?>[] SERVICES = new Class[] {
com.android.systemui.tuner.TunerService.class,
com.android.systemui.keyguard.KeyguardViewMediator.class,
com.android.systemui.recents.Recents.class,
com.android.systemui.volume.VolumeUI.class,
Divider.class,
com.android.systemui.statusbar.SystemBars.class,
com.android.systemui.usb.StorageNotification.class,
com.android.systemui.power.PowerUI.class,
com.android.systemui.media.RingtonePlayer.class,
com.android.systemui.keyboard.KeyboardUI.class,
com.android.systemui.tv.pip.PipUI.class,
com.android.systemui.shortcut.ShortcutKeyDispatcher.class
};
此处以SystemBars为例来展开
3.5 startServicesIfNeeded
[-> SystemUIApplication.java]
private void startServicesIfNeeded(Class<?>[] services) {
if (mServicesStarted) {
return;
}
if (!mBootCompleted) {
if ("1".equals(SystemProperties.get("sys.boot_completed"))) {
mBootCompleted = true;
}
}
final int N = services.length;
for (int i=0; i<N; i++) {
Class<?> cl = services[i];
try {
//初始化对象
Object newService = SystemUIFactory.getInstance().createInstance(cl);
mServices[i] = (SystemUI) ((newService == null) ? cl.newInstance() : newService);
} catch (Exception ex) {
...
}
mServices[i].mContext = this;
mServices[i].mComponents = mComponents;
//【见小节3.6】
mServices[i].start();
if (mBootCompleted) {
mServices[i].onBootCompleted();
}
}
mServicesStarted = true;
}
3.6 SystemBars.start
[-> SystemBars.java]
public void start() {
mServiceMonitor = new ServiceMonitor(TAG, DEBUG,
mContext, Settings.Secure.BAR_SERVICE_COMPONENT, this);
mServiceMonitor.start(); //当远程服务不存在，则执行下面的onNoService
}
public void onNoService() {
//【见小节3.7】
createStatusBarFromConfig()；
}
3.7 createStatusBarFromConfig
[-> SystemBars.java]
private void createStatusBarFromConfig() {
//config_statusBarComponent是指PhoneStatusBar
final String clsName = mContext.getString(R.string.config_statusBarComponent);
Class<?> cls = null;
try {
cls = mContext.getClassLoader().loadClass(clsName);
} catch (Throwable t) {
...
}
try {
mStatusBar = (BaseStatusBar) cls.newInstance();
} catch (Throwable t) {
...
}
mStatusBar.mContext = mContext;
mStatusBar.mComponents = mComponents;
//【见小节3.8】
mStatusBar.start();
}
config_statusBarComponent的定义位于文件config.xml中，其值为PhoneStatusBar。
3.8 PhoneStatusBar
[-> PhoneStatusBar.java]
public void start() {
...
super.start(); //此处调用BaseStatusBar
}
3.9 BaseStatusBar
[-> BaseStatusBar.java]
public void start() {
...
//安装通知的初始化状态【3.10】
mNotificationListener.registerAsSystemService(mContext,
new ComponentName(mContext.getPackageName(), getClass().getCanonicalName()),
UserHandle.USER_ALL);
...
createAndAddWindows(); //添加状态栏
...
}
3.10 NLS.registerAsSystemService
[-> NotificationListenerService.java]
public void registerAsSystemService(Context context, ComponentName componentName,
int currentUser) throws RemoteException {
if (mWrapper == null) {
mWrapper = new NotificationListenerWrapper();
}
mSystemContext = context;
//获取NMS的接口代理对象
INotificationManager noMan = getNotificationInterface();
//运行在主线程的handler
mHandler = new MyHandler(context.getMainLooper());
mCurrentUser = currentUser;
//经过binder调用，向system_server中的NMS注册监听器【3.11】
noMan.registerListener(mWrapper, componentName, currentUser);
}
经过binder调用，向system_server中的NMS注册监听器
3.11 registerListener
[-> NMS.java]
private final IBinder mService = new INotificationManager.Stub() {
...
public void registerListener(final INotificationListener listener,
final ComponentName component, final int userid) {
enforceSystemOrSystemUI("INotificationManager.registerListener");
//此处的INotificationListener便是NotificationListenerWrapper代理对象 【3.11.1】
mListeners.registerService(listener, component, userid);
}
}
mListeners的对象类型为ManagedServices。此处的INotificationListener便是NotificationListenerWrapper的代理对象
3.11.1 registerService
[-> ManagedServices.java]
public void registerService(IInterface service, ComponentName component, int userid) {
//【3.11.2】
ManagedServiceInfo info = registerServiceImpl(service, component, userid);
if (info != null) {
onServiceAdded(info);
}
}
3.11.2 registerService
[-> ManagedServices.java]
private ManagedServiceInfo registerServiceImpl(final IInterface service,
final ComponentName component, final int userid) {
//将NotificationListenerWrapper对象保存到ManagedServiceInfo.service
ManagedServiceInfo info = newServiceInfo(service, component, userid,
true, null, Build.VERSION_CODES.LOLLIPOP);
//【3.11.3】
return registerServiceImpl(info);
}
3.11.3 registerServiceImpl
[-> ManagedServices.java]
private ManagedServiceInfo registerServiceImpl(ManagedServiceInfo info) {
synchronized (mMutex) {
try {
info.service.asBinder().linkToDeath(info, 0);
mServices.add(info);
return info;
} catch (RemoteException e) {
}
}
return null;
}
可见，前面的listener的对端便是运行在systemui中的NotificationListenerWrapper的代理对象。
三. 小结
整个过程涉及到3个Handler都是运行在system_server的主线程：NMS的mHandler，NLS的mHandler以及BaseStatusBar的mHandler。
一次通知发送的过程，在system_server进程里面经过了步骤[2.3]，[2.4]的两次异步调用，进入systemui进程，也经历[2.6]，[2.8]共两次异步调用。 本身是异步调用，再进过一次异步意义并不大。
另外，这里需要注意的是前台服务也会显示通知，该通知是为了提升服务的优先级，并且让用户可感知该服务的存在，以防止进程被杀，比如音乐播放。 对于常规的通知可通过点击通知(允许清除的通知)或者点击通知栏的清除按钮来清除。
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