BroadcastReceiver的工作过程
BroadcastReceiver的工作过程
本篇博客不介绍BroadcastReceiver的具体使用，只对广播的注册过程和发送接收过程进行源码分析。
介绍一下几个重要的概念：
1.Context：http://blog.csdn.net/qinjuning/article/details/7310620
2.ActivityThread、ApplicationThread：http://blog.csdn.net/myarrow/article/details/14223493
广播的注册过程
广播分为静态注册和动态注册，其中静态注册的广播在应用安装时由系统自动完成注册，是由PMS来完成整个注册过程的，其他三大组件都是在应用安装时由PMS解析并注册的。这里只分析广播的动态注册。
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);
}
mBase就是ContextImpl。
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter,
String broadcastPermission, Handler scheduler) {
return registerReceiverInternal(receiver, getUserId(),
filter, broadcastPermission, scheduler, getOuterContext());
}
private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
IntentFilter filter, String broadcastPermission,
Handler scheduler, Context context) {
IIntentReceiver rd = null;
if (receiver != null) {
if (mPackageInfo != null && context != null) {
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
rd = mPackageInfo.getReceiverDispatcher(
receiver, context, scheduler,
mMainThread.getInstrumentation(), true);
} else {
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
rd = new LoadedApk.ReceiverDispatcher(
receiver, context, scheduler, null, true).getIIntentReceiver();
}
}
try {
return ActivityManagerNative.getDefault().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName,
rd, filter, broadcastPermission, userId);
} catch (RemoteException e) {
return null;
}
}
分析：系统首先从mPackageInfo获取IItentReceiver（Binder接口，具体实现是LoadedApk.RecevierDispatcher.InnerRecevier）对象，然后再采用跨进程的方式向AMS发送广播注册的请求。RecevierDispatcher内部保存了BroadcastRecevier和InnerRecevier，这样当接收广播时，RecevierDispatcher可以方便的调用BroadcastRecevier的onReceive方法，和Service的实现原理类似。
LoadedApk#getReceiverDispatcher
public IIntentReceiver getReceiverDispatcher(BroadcastReceiver r,
Context context, Handler handler,
Instrumentation instrumentation, boolean registered) {
synchronized (mReceivers) {
LoadedApk.ReceiverDispatcher rd = null;
ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher> map = null;
if (registered) {
map = mReceivers.get(context);
if (map != null) {
rd = map.get(r);
}
}
if (rd == null) {
rd = new ReceiverDispatcher(r, context, handler,
instrumentation, registered);
if (registered) {
if (map == null) {
map = new ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher>();
mReceivers.put(context, map);
}
map.put(r, rd);
}
} else {
rd.validate(context, handler);
}
rd.mForgotten = false;
return rd.getIIntentReceiver();
}
}
显然，getReceiverDispatcher方法重新创建了一个ReceiverDispatcher对象并将其保存的InnerReceiver对象作为返回值返回，其中InnerReceiver对象和BroadcastReceiver都是在ReceiverDispatcher的构造方法中被保存下来。
由于注册广播的真正实现过程在AMS中，看一下源码。
AMS#registerReceiver
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId) {
...........
mRegisteredReceivers.put(receiver.asBinder(), rl);
} else if (rl.uid != callingUid) {
throw new IllegalArgumentException(
"Receiver requested to register for uid " + callingUid
+ " was previously registered for uid " + rl.uid);
} else if (rl.pid != callingPid) {
throw new IllegalArgumentException(
"Receiver requested to register for pid " + callingPid
+ " was previously registered for pid " + rl.pid);
} else if (rl.userId != userId) {
throw new IllegalArgumentException(
"Receiver requested to register for user " + userId
+ " was previously registered for user " + rl.userId);
}
BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
permission, callingUid, userId);
rl.add(bf);
if (!bf.debugCheck()) {
Slog.w(TAG, "==> For Dynamic broadcast");
}
mReceiverResolver.addFilter(bf);
........
}
上面截取了部分关键代码分析：把远程的InnerReceiver对象以及IntentFilter对象储存起来。这样整个广播的注册过程就完成了。
广播的发送和接受过程
当通过send方法来发送广播时，AMS会查找出匹配的广播接受者并将广播的发送给它们处理。
先从发送分析。ContextWrapper的sendBroadcast方法把事情交给ContextImpl去处理。
@Override
public void sendBroadcast(Intent intent, String receiverPermission, int appOp) {
warnIfCallingFromSystemProcess();
String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
String[] receiverPermissions = receiverPermission == null ? null
: new String[] {receiverPermission};
try {
intent.prepareToLeaveProcess();
ActivityManagerNative.getDefault().broadcastIntent(
mMainThread.getApplicationThread(), intent, resolvedType, null,
Activity.RESULT_OK, null, null, receiverPermissions, appOp, null, false, false,
getUserId());
} catch (RemoteException e) {
throw new RuntimeException("Failure from system", e);
}
}它直接向AMS发起了一个异步请求用于发送广播。
AMS#broadcastIntent
public final int broadcastIntent(IApplicationThread caller,
Intent intent, String resolvedType, IIntentReceiver resultTo,
int resultCode, String resultData, Bundle resultExtras,
String[] requiredPermissions, int appOp, Bundle options,
boolean serialized, boolean sticky, int userId) {
enforceNotIsolatedCaller("broadcastIntent");
synchronized(this) {
intent = verifyBroadcastLocked(intent);
final ProcessRecord callerApp = getRecordForAppLocked(caller);
final int callingPid = Binder.getCallingPid();
final int callingUid = Binder.getCallingUid();
final long origId = Binder.clearCallingIdentity();
int res = broadcastIntentLocked(callerApp,
callerApp != null ? callerApp.info.packageName : null,
intent, resolvedType, resultTo, resultCode, resultData, resultExtras,
requiredPermissions, appOp, null, serialized, sticky,
callingPid, callingUid, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}broadcastIntent调用了broadcastIntentLocked方法，在broadcastIntentLocked的内部根据intent-filter查找出匹配的广播接受者并经过一系列的条件过滤，最终将满足条件的广播接受者添加到BroadcastQueue中，接着BroadcastQueue就会将广播发送给相应的广播接受者。源码如下
int NR = registeredReceivers != null ? registeredReceivers.size() : 0;
if (!ordered && NR > 0) {
// If we are not serializing this broadcast, then send the
// registered receivers separately so they don't wait for the
// components to be launched.
final BroadcastQueue queue = broadcastQueueForIntent(intent);
BroadcastRecord r = new BroadcastRecord(queue, intent, callerApp,
callerPackage, callingPid, callingUid, resolvedType, requiredPermissions,
appOp, brOptions, registeredReceivers, resultTo, resultCode, resultData,
resultExtras, ordered, sticky, false, userId);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing parallel broadcast " + r);
final boolean replaced = replacePending && queue.replaceParallelBroadcastLocked(r);
if (!replaced) {
queue.enqueueParallelBroadcastLocked(r);
queue.scheduleBroadcastsLocked();
}
registeredReceivers = null;
NR = 0;BroadcastQueue中广播的发送过程的实现：
BroadcastQueue#scheduleBroadcastsLocked
public void scheduleBroadcastsLocked() {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Schedule broadcasts ["
+ mQueueName + "]: current="
+ mBroadcastsScheduled);
if (mBroadcastsScheduled) {
return;
}
mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this));
mBroadcastsScheduled = true;
}并没有立即发送广播而是发送了BROADCAST_INTENT_MSG消息，BroadcastQueue收到消息后调用processNextBroadcast方法。
对普通广播的处理如下：
// First, deliver any non-serialized broadcasts right away.
while (mParallelBroadcasts.size() > 0) {
r = mParallelBroadcasts.remove(0);
r.dispatchTime = SystemClock.uptimeMillis();
r.dispatchClockTime = System.currentTimeMillis();
final int N = r.receivers.size();
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Processing parallel broadcast ["
+ mQueueName + "] " + r);
for (int i=0; i
Object target = r.receivers.get(i);
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Delivering non-ordered on [" + mQueueName + "] to registered "
+ target + ": " + r);
deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false);
}
addBroadcastToHistoryLocked(r);
if (DEBUG_BROADCAST_LIGHT) Slog.v(TAG_BROADCAST, "Done with parallel broadcast ["
+ mQueueName + "] " + r);
} 无序广播存储在mParallelBroadcasts中，系统遍历mParallelBroadcasts并将其中的广播通过deliverToRegisteredReceiverLocked发送接受者。
deliverToRegisteredReceiverLocked方法负责将一个广播发送给一个特定的接受者，它内部调用了performReceiveLocked方法具体实现发送过程。
private static void performReceiveLocked(ProcessRecord app, IIntentReceiver receiver,
Intent intent, int resultCode, String data, Bundle extras,
boolean ordered, boolean sticky, int sendingUser) throws RemoteException {
// Send the intent to the receiver asynchronously using one-way binder calls.
if (app != null) {
if (app.thread != null) {
// If we have an app thread, do the call through that so it is
// correctly ordered with other one-way calls.
app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode,
data, extras, ordered, sticky, sendingUser, app.repProcState);
} else {
// Application has died. Receiver doesn't exist.
throw new RemoteException("app.thread must not be null");
}
} else {
receiver.performReceive(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
}
}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);
receiver.performReceive(intent, resultCode, dataStr, extras, ordered,
sticky, sendingUser);
}InnerRecevier的performReceive方法会调用LoadedApk.ReceiverDispatcher的performRecieve方法。
LoadedApk.ReceiverDispatcher#performRecieve
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
if (ActivityThread.DEBUG_BROADCAST) {
int seq = intent.getIntExtra("seq", -1);
Slog.i(ActivityThread.TAG, "Enqueueing broadcast " + intent.getAction() + " seq=" + seq
+ " to " + mReceiver);
}
Args args = new Args(intent, resultCode, data, extras, ordered,
sticky, sendingUser);
if (!mActivityThread.post(args)) {
if (mRegistered && ordered) {
IActivityManager mgr = ActivityManagerNative.getDefault();
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing sync broadcast to " + mReceiver);
args.sendFinished(mgr);
}
}
}
创建一个Args对象并通过mActivityThread的post方法来执行Args中的逻辑，而Args实现了Runnable接口。mActivityThread就是ActivityThread的Handler H。
final BroadcastReceiver receiver = mReceiver;
receiver.setPendingResult(this);
receiver.onReceive(mContext, intent);这时BroadcastReceiver的onReceive方法被执行了，也就是说应用已经接收到广播了，同时onReceive方法是在广播接收者的主线程中被调用的。