动态注册过程
ContextWrapper#registerReceiver（以下代码基于API26）
动态注册的过程从ContextWrapper的registerReceiver方法开始
@Override
public Intent registerReceiver(
BroadcastReceiver receiver, IntentFilter filter) {
return mBase.registerReceiver(receiver, filter);
}
和Activity、Service一样，ContextWrapper没有做任何操作，而是把任务交给了ContextImpl（mBase的实现类型是ContextImpl）来完成。接着看ContextImpl的registerReceiver方法。
ContextImpl#registerReceiver
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
return registerReceiver(receiver, filter, null, null);
}
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter,
String broadcastPermission, Handler scheduler) {
return registerReceiverInternal(receiver, getUserId(),
filter, broadcastPermission, scheduler, getOuterContext(), 0);
}
又调用自己的registerReceiverInternal方法
ContextImpl#registerReceiverInternal
private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
IntentFilter filter, String broadcastPermission,
Handler scheduler, Context context, int flags) {
IIntentReceiver rd = null;
//广播接收器不为空时，获取IIntentReceiver对象（IIntentReceiver是一个Binder接口）
if (receiver != null) {
if (mPackageInfo != null && context != null) {
//...
rd = mPackageInfo.getReceiverDispatcher(
receiver, context, scheduler,
mMainThread.getInstrumentation(), true);
} else {
//...
rd = new LoadedApk.ReceiverDispatcher(
receiver, context, scheduler, null, true).getIIntentReceiver();
}
}
try {
//通过AMS的registerReceiver方法注册广播
final Intent intent = ActivityManager.getService().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName, rd, filter,
broadcastPermission, userId, flags);
//...
return intent;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
为什么需要先将BroadcastReceiver转化为IIntentReceiver？
因为广播的注册过程是一个进程间通信的进程，而BroadcastReceiver是Android的一个组件，不能直接跨进程传递，而IIntentReceiver是一个Binder接口，可以跨进程，所以需要先将BroadcastReceiver转化为IIntentReceiver。
下面看一下IIntentReceiver的获取，无论是哪种情况，最后都是调用LoadedApk.ReceiverDispatcher的getIIntentReceiver方法
LoadedApk.ReceiverDispatcher#getIIntentReceiver
IIntentReceiver getIIntentReceiver() {
return mIIntentReceiver;
}
其中mIIntentReceiver是一个IIntentReceiver.Stub对象
final IIntentReceiver.Stub mIIntentReceiver;
mIIntentReceiver是在ReceiverDispatcher的构造方法中初始化的
ReceiverDispatcher(BroadcastReceiver receiver, Context context,
Handler activityThread, Instrumentation instrumentation,
boolean registered) {
//...
mIIntentReceiver = new InnerReceiver(this, !registered);
//...
}
可以看到，最终IIntentReceiver的实现类是LoadedApk.ReceiverDispatcher.InnerReceiver
继续看回注册过程：
//ActivityManager.getService()返回的是ActivityManagerService对象
final Intent intent = ActivityManager.getService().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName, rd, filter,
broadcastPermission, userId, flags);
//...
return intent;
可以看到，注册过程的真正实现是AMS的registerReceiver方法
ActivityManagerService#registerReceiver
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId,
int flags) {
//...
synchronized (this) {
//...
//获取该receiver（IIntentReceiver对象）对应的ReceiverList
//ReceiverList继承于ArrayList<BroadcastFilter>，是一个存储BroadcastFilter的集合
ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
//若rl为空，则根据receiver创建对应的ReceiverList，并使两者建立映射关系存入HashMap中
if (rl == null) {
rl = new ReceiverList(this, callerApp, callingPid, callingUid,
userId, receiver);
//...
mRegisteredReceivers.put(receiver.asBinder(), rl);
}
//...
//BroadcastFilter继承于IntentFilter
BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
permission, callingUid, userId, instantApp, visibleToInstantApps);
//将该BroadcastFilter添加进ReceiverList中
rl.add(bf);
mReceiverResolver.addFilter(bf);
//...
}
}
其中mRegisteredReceivers的定义如下：
/**
* Keeps track of all IIntentReceivers that have been registered for broadcasts.
* Hash keys are the receiver IBinder, hash value is a ReceiverList.
*/
final HashMap<IBinder, ReceiverList> mRegisteredReceivers = new HashMap<>();
可以看到，一个IIntentReceiver对应着一个ReceiverList
最终，通过HashMap把IIntentReceiver与对应的ReceiverList保存起来；而ReceiverList又把可以启动该BroadcastReceiver的IntentFilter保存起来。
发送、接收普通广播
以下是一个发送普通广播的例子：
Intent intent = new Intent();
intent.setAction("FIRST_RECEIVER");
sendBroadcast(intent); //发送广播
仍然是从ContextWrapper开始，调用其sendBroadcast方法
ContextWrapper#sendBroadcast
@Override
public void sendBroadcast(Intent intent) {
mBase.sendBroadcast(intent);
}
依然是交给ContextImpl来处理，调用其sendBroadcast方法
ContextImpl#sendBroadcast
@Override
public void sendBroadcast(Intent intent) {
//...
try {
intent.prepareToLeaveProcess(this);
//调用AMS的broadcastIntent方法
ActivityManager.getService().broadcastIntent(
mMainThread.getApplicationThread(), intent, resolvedType, null,
Activity.RESULT_OK, null, null, null, AppOpsManager.OP_NONE, null, false, false,
getUserId());
} //...
}
ContextImpl也没做什么，它直接调用AMS的broadcastIntent方法
ActivityManagerService#broadcastIntent
public final int broadcastIntent(IApplicationThread caller,
Intent intent, String resolvedType, IIntentReceiver resultTo,
int resultCode, String resultData, Bundle resultExtras,
String[] requiredPermissions, int appOp, Bundle bOptions,
boolean serialized, boolean sticky, int userId) {
//...
synchronized(this) {
//...
int res = broadcastIntentLocked(callerApp,
callerApp != null ? callerApp.info.packageName : null,
intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
requiredPermissions, appOp, bOptions, serialized, sticky,
callingPid, callingUid, userId);
//...
return res;
}
}
继续调用broadcastIntentLocked方法
ActivityManagerService#broadcastIntentLocked
final int broadcastIntentLocked(ProcessRecord callerApp,
String callerPackage, Intent intent, String resolvedType,
IIntentReceiver resultTo, int resultCode, String resultData,
Bundle resultExtras, String[] requiredPermissions, int appOp, Bundle bOptions,
boolean ordered, boolean sticky, int callingPid, int callingUid, int userId) {
//...
//添加这个标志后，广播不会发送给已经停止的应用
intent.addFlags(Intent.FLAG_EXCLUDE_STOPPED_PACKAGES);
//...
//判断是否有添加FLAG_RECEIVER_REPLACE_PENDING标记位
//这个flag将会将之前的Intent替代掉。加了这个flag，在发送一系列的这样的Intent之后， //中间有些Intent有可能在你还没有来得及处理的时候，就被替代掉了。
final boolean replacePending =
(intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;
//...
if ((receivers != null && receivers.size() > 0)
|| resultTo != null) {
//获取AMS的广播队列
BroadcastQueue queue = broadcastQueueForIntent(intent);
//先将匹配的广播接收器封装成一个BroadcastRecord对象r
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, callerInstantApp, resolvedType,
requiredPermissions, appOp, brOptions, receivers, resultTo, resultCode,
resultData, resultExtras, ordered, sticky, false, userId);
//...
final BroadcastRecord oldRecord =
replacePending ? queue.replaceOrderedBroadcastLocked(r) : null;
if (oldRecord != null) {
// Replaced, fire the result-to receiver.
//...
} else {
//将BroadcastRecord对象r插入广播队列queue中
queue.enqueueOrderedBroadcastLocked(r);
//在BroadcastRecord中发送广播
queue.scheduleBroadcastsLocked();
}
} //...
return ActivityManager.BROADCAST_SUCCESS;
}
该方法最终将满足条件的广播接收器封装到BroadcastRecord中，并添加到广播队列BroadcastQueue中，通过BroadcastQueue的scheduleBroadcastsLocked方法发送给相应的广播接收器。接下来看一下BroadcastQueue的scheduleBroadcastsLocked方法。
BroadcastQueue#scheduleBroadcastsLocked
public void scheduleBroadcastsLocked() {
//...
//mBroadcastsScheduled是一个布尔变量，表明是否发送过BROADCAST_INTENT_MSG消息
if (mBroadcastsScheduled) {
return;
}
//发送BROADCAST_INTENT_MSG消息
mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this));
mBroadcastsScheduled = true;
}
对BROADCAST_INTENT_MSG消息的处理是
case BROADCAST_INTENT_MSG: {
//...
processNextBroadcast(true);
} break;
可以看到，收到BROADCAST_INTENT_MSG消息后，执行processNextBroadcast方法
BroadcastQueue#processNextBroadcast
final void processNextBroadcast(boolean fromMsg) {
synchronized(mService) {
BroadcastRecord r;
//...
//如果是从BROADCAST_INTENT_MSG消息而来，重置mBroadcastsScheduled
if (fromMsg) {
mBroadcastsScheduled = false;
}
//发送无序广播，无序广播存储在mParallelBroadcasts中
while (mParallelBroadcasts.size() > 0) {
r = mParallelBroadcasts.remove(0);
//...
final int N = r.receivers.size();
for (int i=0; i<N; i++) {
Object target = r.receivers.get(i);
//该方法负责将广播发送给特定的接收器
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false, i);
}
addBroadcastToHistoryLocked(r);
}
}
可以看到，将广播发送到对应接收器的过程是通过deliverToRegisteredReceiverLocked方法实现的
BroadcastQueue#deliverToRegisteredReceiverLocked
private void deliverToRegisteredReceiverLocked(BroadcastRecord r,
BroadcastFilter filter, boolean ordered, int index) {
//...
try {
if (filter.receiverList.app != null && filter.receiverList.app.inFullBackup) {
//...
} else {
//通过该方法完成具体的发送过程
performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver,
new Intent(r.intent), r.resultCode, r.resultData,
r.resultExtras, r.ordered, r.initialSticky, r.userId);
}
//...
} //...
}
继续看performReceiveLocked方法
BroadcastQueue#performReceiveLocked
void performReceiveLocked(ProcessRecord app, IIntentReceiver receiver,
Intent intent, int resultCode, String data, Bundle extras,
boolean ordered, boolean sticky, int sendingUser) throws RemoteException {
if (app != null) {
if (app.thread != null) {
try {
//app.thread的实现是ActivityThread.ApplicationThread
app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,
data, extras, ordered, sticky, sendingUser, app.repProcState);
} //...
} //...
} //...
}
接着调用ApplicationThread的scheduleRegisteredReceiver方法
ActivityThread.ApplicationThread#scheduleRegisteredReceiver
public void scheduleRegisteredReceiver(IIntentReceiver receiver, Intent intent,
int resultCode, String dataStr, Bundle extras, boolean ordered,
boolean sticky, int sendingUser, int processState) throws RemoteException {
updateProcessState(processState, false);
//调用InnerReceiver的performReceive方法
receiver.performReceive(intent, resultCode, dataStr, extras, ordered,
sticky, sendingUser);
}
ReceiverDispatcher.InnerReceiver
final static class InnerReceiver extends IIntentReceiver.Stub {
final WeakReference<LoadedApk.ReceiverDispatcher> mDispatcher;
final LoadedApk.ReceiverDispatcher mStrongRef;
InnerReceiver(LoadedApk.ReceiverDispatcher rd, boolean strong) {
mDispatcher = new WeakReference<LoadedApk.ReceiverDispatcher>(rd);
mStrongRef = strong ? rd : null;
}
@Override
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
final LoadedApk.ReceiverDispatcher rd;
if (intent == null) {
rd = null;
} else {
rd = mDispatcher.get();
}
//...
if (rd != null) {
//调用LoadedApk.ReceiverDispatcher的performReceive方法
rd.performReceive(intent, resultCode, data, extras,
ordered, sticky, sendingUser);
} //...
}
}
继续调用LoadedApk.ReceiverDispatcher的performReceive方法
LoadedApk.ReceiverDispatcher#performReceive
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
//Args是LoadedApk.ReceiverDispatcher的内部类
final Args args = new Args(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
//...
//mActivityThread是一个Handler对象，指向ActivityThread中的handler对象
if (intent == null || !mActivityThread.post(args.getRunnable())) {
//...
}
}
在post里面执行了Args的getRunnable方法，其实现如下
LoadedApk.ReceiverDispatcher.Args#getRunnable
public final Runnable getRunnable() {
return () -> {
final BroadcastReceiver receiver = mReceiver;
//...
try {
//...
//回调了BoradcastReceiver的onReceive方法
receiver.onReceive(mContext, intent);
} //...
};
}
可以看到，最终在Args抛出的一个Runnable的run方法中回调了BoradcastReceiver的onReceive方法，并且是在广播接收器的主线程中执行的。
至此，普通广播的发送及接收过程分析完毕。
参考
- 《Android开发艺术探索》
- BroadcastReceiver源码解析（二）
