Android中的廣播分爲動態廣播和靜態廣播，靜態廣播需要在清單文件中註冊，動態廣播使用代碼在需要的地方註冊，這裏只分析動態廣播的註冊過程，
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註冊過程
動態的廣播註冊調用ContextWrapper的registerReceiver方法。mBase是Context類，具體的實現是在ContextImpl中。
@Override public Intent registerReceiver( BroadcastReceiver receiver, IntentFilter filter) { return mBase.registerReceiver(receiver, filter); }-
ContextImpl的registerReceiver方法
該方法最終調用registerReceiverInternal方法。
@Override public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) { return registerReceiver(receiver, filter, null, null); } -
ContextImpl的registerReceiverInternal方法
該方法內最終調用ActivityManagerService的registerReceiver方法。並將ThreadActivity內部的ApplicationThread傳入。這個過程涉及到跨進程，因此使用了IIntentReceiver這個Binder接口，它的具體實現時LoadedApk.ReceiverDispatcher.InnerReceiver，創建了ReceiverDispatcher對象，並將BroadCastReciver及InnerReceiver保存在ReceiverDispatcher對象中。
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(); } 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 { 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(); } } -
ActivityManagerService的registerReceiver方法
在該方法中將會將遠程的InnerReceiver以及BroadcastFilter保存起來。
... mRegisteredReceivers.put(receiver.asBinder(), rl); .... BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage, permission, callingUid, userId, instantApp, visibleToInstantApps); if (rl.containsFilter(filter)) { Slog.w(TAG, "Receiver with filter " + filter + " already registered for pid " + rl.pid + ", callerPackage is " + callerPackage); } else { rl.add(bf); if (!bf.debugCheck()) { Slog.w(TAG, "==> For Dynamic broadcast"); } mReceiverResolver.addFilter(bf); } ...
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發佈過程
- ContexImpl的sendBroadcast
廣播的發送會調用Context的sendBroadcast方法，具體實現依然在ContextImpl中，
在該方法中調用了AMS的broadcastIntent方法 。
@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(); } }
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ActivityManagerService的broadcastIntent
在該方法中通過intent獲取BroadcastQueue一個隊列，最後調用scheduleBroadcastsLocked方法。
... 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); if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Enqueueing parallel broadcast " + r); final boolean replaced = replacePending && (queue.replaceParallelBroadcastLocked(r) != null); // Note: We assume resultTo is null for non-ordered broadcasts. if (!replaced) { queue.enqueueParallelBroadcastLocked(r); queue.scheduleBroadcastsLocked(); } ... -
BroadcastQueue的scheduleBroadcastsLocked方法
在該方法內發送一個BROADCAST_INTENT_MSG狀態的消息。
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; }BROADCAST_INTENT_MSG的消息處理如下，調用processNextBroadcast方法，並接着調用deliverToRegisteredReceiverLocked方法
private final class BroadcastHandler extends Handler { public BroadcastHandler(Looper looper) { super(looper, null, true); } @Override public void handleMessage(Message msg) { switch (msg.what) { case BROADCAST_INTENT_MSG: { if (DEBUG_BROADCAST) Slog.v( TAG_BROADCAST, "Received BROADCAST_INTENT_MSG"); processNextBroadcast(true); } break; case BROADCAST_TIMEOUT_MSG: { synchronized (mService) { broadcastTimeoutLocked(true); } } break; } } } -
deliverToRegisteredReceiverLocked方法
在該方法內調用performReceiveLocked方法。
... performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver, new Intent(r.intent), r.resultCode, r.resultData, r.resultExtras, r.ordered, r.initialSticky, r.userId); ... -
performReceiveLocked方法
在該方法內調用app.thread.scheduleRegisteredReceiver方法，也就是ActiivtyThread內的ApplicationThread的scheduleRegisteredReceiver方法。
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. try { app.thread.scheduleRegisteredReceiver(receiver, intent, resultCode, data, extras, ordered, sticky, sendingUser, app.repProcState); // TODO: Uncomment this when (b/28322359) is fixed and we aren't getting // DeadObjectException when the process isn't actually dead. //} catch (DeadObjectException ex) { // Failed to call into the process. It's dying so just let it die and move on. // throw ex; } catch (RemoteException ex) { // Failed to call into the process. It's either dying or wedged. Kill it gently. synchronized (mService) { Slog.w(TAG, "Can't deliver broadcast to " + app.processName + " (pid " + app.pid + "). Crashing it."); app.scheduleCrash("can't deliver broadcast"); } throw ex; } } 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的scheduleRegisteredReceiver方法
在該方法內調用IIntentReceiver這個Binder接口的performReceive，也就調用上文說到的LoadedAPK.ReceiverDispatcher.InnerReceiver的performReceive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.performReceive(intent, resultCode, dataStr, extras, ordered, sticky, sendingUser); } -
InnerReceiver的performReceive方法
在該方法內調用LoadedApk.ReceiverDispatcher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; .... rd.performReceive(intent, resultCode, data, extras, ordered, sticky, sendingUser); ... } -
ReceiverDispatcher的performReceive方法
在該方法中調用了mActivityThread.post(args.getRunnable())，mActivityThread是一個Handler，args是Args對象，通過getRunnable獲取一個Runnable對象，並執行run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); if (intent == null) { Log.wtf(TAG, "Null intent received"); } else { if (ActivityThread.DEBUG_BROADCAST) { int seq = intent.getIntExtra("seq", -1); Slog.i(ActivityThread.TAG, "Enqueueing broadcast " + intent.getAction() + " seq=" + seq + " to " + mReceiver); } } if (intent == null || !mActivityThread.post(args.getRunnable())) { if (mRegistered && ordered) { IActivityManager mgr = ActivityManager.getService(); if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG, "Finishing sync broadcast to " + mReceiver); args.sendFinished(mgr); } } }Runnable的run方法。
在該方法內最終調用BroadcastReciver的onReciver方法。
... try { ClassLoader cl = mReceiver.getClass().getClassLoader(); intent.setExtrasClassLoader(cl); intent.prepareToEnterProcess(); setExtrasClassLoader(cl); receiver.setPendingResult(this); receiver.onReceive(mContext, intent); } catch (Exception e) { ...
總結：當調用廣播的註冊方法時，會將BroadcastReciver保存在LoadedApk.BroadcastDispatcher中，並返回一個IIntentReceiver的Binder的接口，具體的實現是LoadedApk.BroadcastDispatcher.InnerReceiver，然後調用AMS的registerReceiver方法將IIntentReceiver和BroadcastFilter存儲起來。當調用廣播的發送方法時，會通過AMS調用broadcastIntent方法，最終調用ActivityThread內部類的ApplicationThread中的scheduleRegisteredReceiver，然後調用IIntentReceiver這個Binder類型的實現類IntentReceiver的performReceive，最終調用BroadcastReciver的onReciver方法。在這個過程中AMS持有IApplicationThread和IIntentReceiver這兩個Binder類型的接口。