一、BroadcastReceiver源码解析
（1）BroadcastReceiver注册过程
- 注册过程是从ContextWraper的registerReceiver方法开始的
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
//ContextWrapper是mBase的代理，mBase成员变量其实是ContextImpl。
return mBase.registerReceiver(receiver, filter);
}
//ContextImpl.java
@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);
}
private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
IntentFilter filter, String broadcastPermission,
Handler scheduler, Context context, int flags) {
IIntentReceiver rd = null;
if (receiver != null) {
if (mPackageInfo != null && context != null) {
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
//注释一
rd = mPackageInfo.getReceiverDispatcher(
receiver, context, scheduler,
mMainThread.getInstrumentation(), true);
} else {
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
//注释二
rd = new LoadedApk.ReceiverDispatcher(
receiver, context, scheduler, null, true).getIIntentReceiver();
}
}
try {
//注释三
final Intent intent = ActivityManager.getService().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName, rd, filter,
broadcastPermission, userId, flags);
if (intent != null) {
intent.setExtrasClassLoader(getClassLoader());
intent.prepareToEnterProcess();
}
return intent;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
- 注释一：将广播接收者及其他参数封装成一个IIntentReceiver对象
- 注释二：最终返回的是IIntentReceiver.Stub类型的对象InnerReceiver，该类实现了IIntentReceiver接口并继承Binder。
- 注释三：基于Binder机制，通过调用代理对象IActivityManager的方法，使得系统服务ActivityManagerService对应的方法被调用。因此，注册的操作就交给了系统服务ActivityManagerService来处理了。
- 查看LoadedApk.ReceiverDispatcher源码
ReceiverDispatcher(BroadcastReceiver receiver, Context context,
Handler activityThread, Instrumentation instrumentation,
boolean registered) {
if (activityThread == null) {
throw new NullPointerException("Handler must not be null");
}
//初始化IIntentReceiver类，InnerReceiver是IIntentReceiver实现类
mIIntentReceiver = new InnerReceiver(this, !registered);
mReceiver = receiver;
mContext = context;
mActivityThread = activityThread;
mInstrumentation = instrumentation;
mRegistered = registered;
mLocation = new IntentReceiverLeaked(null);
mLocation.fillInStackTrace();
}
- 查看ActivityManagerService.registerReceiver源码
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId,
int flags) {
//code..
synchronized (this) {
//code...
//注释一
ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
if (rl == null) {
rl = new ReceiverList(this, callerApp, callingPid, callingUid,
userId, receiver);
if (rl.app != null) {
final int totalReceiversForApp = rl.app.receivers.size();
//code...
rl.app.receivers.add(rl);
} else {
try {
receiver.asBinder().linkToDeath(rl, 0);
} catch (RemoteException e) {
return sticky;
}
rl.linkedToDeath = true;
}
//注释二
mRegisteredReceivers.put(receiver.asBinder(), rl);
} else if (rl.uid != callingUid) {
//code...(IllegalArgumentException异常)
} else if (rl.pid != callingPid) {
throw new IllegalArgumentException(
//code...(IllegalArgumentException异常)
} else if (rl.userId != userId) {
//code...(IllegalArgumentException异常)
}
//注释三
BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
permission, callingUid, userId, instantApp, visibleToInstantApps);
if (rl.containsFilter(filter)) {
//code...
} else {
rl.add(bf);
//注释四
mReceiverResolver.addFilter(bf);
}
//code...
return sticky;
}
}
- 注释一：每次发来的一个注册请求都会对应ReceiverList中的一条数据。
- 注释二：将客户端传递过来的广播接收器InnerReceiver保存起来。
- 注释三：创建一个BroadcastFilter对象，BroadcastFilter继承自IntentFilter。
- 注释四：将客户端传递过来的IntentFilter也保存起来，这样整个广播注册过程就完成了。
总结
- 客户端：客户端广播注册的时候，loadedApk对应着多个context对象（一个进程对应多个activity和service以及一个application），每个context里面有一张hashmap存放注册的广播接收者（每个activity里面可以注册多个广播，都存放在hashmap里），每张hashmap里面包含许多ReceiverDispatcher（内含binder）；
- AMS：每个客户端的ReceiverDispatcher都对应一个ReceiverList，该ReceiverList中保存着可以启动该广播接收者的IntentFilter列表。而每一个ReceiverList都对应着接收者注册时候的一个Binder对象。
（2）广播的发送与接收
- 广播发送是从ContextWraper的sendBroadcast方法开始的
@Override
public void sendBroadcast(Intent intent) {
mBase.sendBroadcast(intent);
}
//ContextImpl.java
@Override
public void sendBroadcast(Intent intent) {
warnIfCallingFromSystemProcess();
String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
try {
intent.prepareToLeaveProcess(this);
ActivityManager.getService().broadcastIntent(
mMainThread.getApplicationThread(), intent, resolvedType, null,
Activity.RESULT_OK, null, null, null, AppOpsManager.OP_NONE, null, false, false,
getUserId());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
- 查看ActivityManagerService.broadcastIntent源码
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) {
enforceNotIsolatedCaller("broadcastIntent");
synchronized(this) {
intent = verifyBroadcastLocked(intent);
//注释一
final ProcessRecord callerApp = getRecordForAppLocked(caller);
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
//注释二
int res = broadcastIntentLocked(callerApp,
callerApp != null ? callerApp.info.packageName : null,
intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
requiredPermissions, appOp, bOptions, serialized, sticky,
callingPid, callingUid, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}
- 注释一：获取广播发送者的身份
- 注释二：调用broadcastIntentLocked发送广播
- broadcastIntentLocked方法主要用来查找目标广播接收者
@GuardedBy("this")
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) {
intent = new Intent(intent);
//code...
//粘性广播
if (sticky) {
//code...
}
//code...
int NR = registeredReceivers != null ? registeredReceivers.size() : 0;
if (!ordered && NR > 0) {
if (isCallerSystem) {
checkBroadcastFromSystem(intent, callerApp, callerPackage, callingUid,
isProtectedBroadcast, registeredReceivers);
}
//通过传递过来的Intent查找相匹配的的BroadcastReceiver并把它放入到广播队列BroadcastQueue中。
final BroadcastQueue queue = broadcastQueueForIntent(intent);
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, callerInstantApp, resolvedType,
requiredPermissions, appOp, brOptions, registeredReceivers, resultTo,
resultCode, resultData, resultExtras, ordered, sticky, false, userId);
final boolean replaced = replacePending
&& (queue.replaceParallelBroadcastLocked(r) != null);
if (!replaced) {
queue.enqueueParallelBroadcastLocked(r);
//执行广播发送任务
queue.scheduleBroadcastsLocked();
}
registeredReceivers = null;
NR = 0;
}
//code...
return ActivityManager.BROADCAST_SUCCESS;
}
- 查看BroadcastQueue.scheduleBroadcastsLocked源码
public void scheduleBroadcastsLocked() {
if (mBroadcastsScheduled) {
return;
}
//向消息管理器mHandler发送了一个BROADCAST_INTENT_MSG类型的消息
mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this));
mBroadcastsScheduled = true;
}
- handleMessage中调用processNextBroadcast(true)方法，processNextBroadcast()方法又调用processNextBroadcastLocked(fromMsg, false)方法。
final void processNextBroadcastLocked(boolean fromMsg, boolean skipOomAdj) {
BroadcastRecord r;
mService.updateCpuStats();
//fromMsg表示是否为BROADCAST_INTENT_MSG类型的消息
if (fromMsg) {
mBroadcastsScheduled = false;
}
//处理mParallelBroadcasts中的广播转发任务
while (mParallelBroadcasts.size() > 0) {
r = mParallelBroadcasts.remove(0);
r.dispatchTime = SystemClock.uptimeMillis();
r.dispatchClockTime = System.currentTimeMillis();
if (Trace.isTagEnabled(Trace.TRACE_TAG_ACTIVITY_MANAGER)) {
Trace.asyncTraceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER,
createBroadcastTraceTitle(r, BroadcastRecord.DELIVERY_PENDING),
System.identityHashCode(r));
Trace.asyncTraceBegin(Trace.TRACE_TAG_ACTIVITY_MANAGER,
createBroadcastTraceTitle(r, BroadcastRecord.DELIVERY_DELIVERED),
System.identityHashCode(r));
}
final int N = r.receivers.size();
for (int i=0; i<N; i++) {
Object target = r.receivers.get(i);
//注释一
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false, i);
}
addBroadcastToHistoryLocked(r);
}
//code...
}
- 注释一：deliverToRegisteredReceiverLocked方法系统在检查广播发送者和接收者的权限之后，调用performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver, new Intent(r.intent), r.resultCode, r.resultData, r.resultExtras, r.ordered, r.initialSticky, r.userId);方法将BroadcastRecord对象r描述的广播交给BroadcastFilter处理。
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 {
//注释一
app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,
data, extras, ordered, sticky, sendingUser, app.repProcState);
} catch (RemoteException ex) {
synchronized (mService) {
app.scheduleCrash("can't deliver broadcast");
}
throw ex;
}
} else {
throw new RemoteException("app.thread must not be null");
}
} else {
receiver.performReceive(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
}
}
- 注释一：app.thread对象是ActivityThread的内部类对象ApplicationThread。
- 查看ApplicationThread对象的scheduleRegisteredReceiver方法。
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);
//receiver指向一个InnerReceiver对象，每个InnerReceiver对象封装了一个广播接收者
receiver.performReceive(intent, resultCode, dataStr, extras, ordered,
sticky, sendingUser);
}
- 查看InnerReceiver中的performReceive方法
@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 (ActivityThread.DEBUG_BROADCAST) {
int seq = intent.getIntExtra("seq", -1);
}
if (rd != null) {
//rd是ReceiverDispatcher的对象，调用rd的performReceive
rd.performReceive(intent, resultCode, data, extras,
ordered, sticky, sendingUser);
} else {
IActivityManager mgr = ActivityManager.getService();
try {
if (extras != null) {
extras.setAllowFds(false);
}
mgr.finishReceiver(this, resultCode, data, extras, false, intent.getFlags());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
}
- 查看ReceiverDispatcher中的performReceive方法
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
final Args args = new Args(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
//code...
//注释一
if (intent == null || !mActivityThread.post(args.getRunnable())) {
if (mRegistered && ordered) {
IActivityManager mgr = ActivityManager.getService();
args.sendFinished(mgr);
}
}
}
- mActivityThread是一个Handler对象，该对象指向ActivityThread中的mH；因此此刻切换到广播接收者所在进程的主线程来执行args，args是一个Runnable对象。
public final Runnable getRunnable() {
return () -> {
//code...
try {
ClassLoader cl = mReceiver.getClass().getClassLoader();
intent.setExtrasClassLoader(cl);
intent.prepareToEnterProcess();
setExtrasClassLoader(cl);
receiver.setPendingResult(this);
//广播接收器BroadcastReceiver的onReceive方法被回调
receiver.onReceive(mContext, intent);
} catch (Exception e) {
//code...
}
//code...
};
}
}
总结
发送广播会查找相应的BroadcastFilter，匹配就会调用相应的远程Binder代理对象通知客户端，最终由客户端的主线程来执行接受者的onReceiver()方法。
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