Android应用程序注册广播接收器（registerReceiver）的过程分析

浏览数：23 / 时间：2015年06月11日

Android应用程序注册广播接收器（registerReceiver）的过程分析 - 老罗的Android之旅 - 博客频道 - CSDN.NET

?? ? ? ?前面我们介绍了Android系统的广播机制，从本质来说，它是一种消息订阅/发布机制，因此，使用这种消息驱动模型的第一步便是订阅消息；而对Android应用程序来说，订阅消息其实就是注册广播接收器，本文将探讨Android应用程序是如何注册广播接收器以及把广播接收器注册到哪里去的。
?? ? ? ?在Android的广播机制中，ActivityManagerService扮演着广播中心的角色，负责系统中所有广播的注册和发布操作，因此，Android应用程序注册广播接收器的过程就把是广播接收器注册到ActivityManagerService的过程。Android应用程序是通过调用ContextWrapper类的registerReceiver函数来把广播接收器BroadcastReceiver注册到ActivityManagerService中去的，而ContextWrapper类本身又借助ContextImpl类来注册广播接收器。
?? ? ? ?在Android应用程序框架中，Activity和Service类都继承了ContextWrapper类，因此，我们可以在Activity或者Service的子类中调用registerReceiver函数来注册广播接收器。Activity、Service、ContextWrapper和ContextImpl这四个类的关系可以参考前面Android系统在新进程中启动自定义服务过程（startService）的原理分析一文中描述的Activity类图。
?? ? ? ?这篇文章还是继续以实例来进行情景分析，所用到的例子便是上一篇文章Android系统中的广播（Broadcast）机制简要介绍和学习计划里面介绍的应用程序了，所以希望读者在继续阅读本文之前，先看看这篇文章；又由于Android应用程序是把广播接器注册到ActivityManagerService中去的，因此，这里又会涉入到Binder进程间通信机制，所以希望读者对Android系统的Binder进程间通信机制有所了解，具体请参考Android进程间通信（IPC）机制Binder简要介绍和学习计划一文。
?? ? ? ?开始进入主题了，在Android系统中的广播（Broadcast）机制简要介绍和学习计划一文所介绍的例子中，注册广播接收器的操作是MainActivity发起的，我们先来看看注册过程的序列图：
?? ? ? ?在分析这个序列图之前，我们先来看一下MainActivity是如何调用registerReceiver函数来注册广播接收器的：
[java] view plain copy print ?
public?class?MainActivity?extends?Activity?implements?OnClickListener?{????
????......??
??
????@Override?????
????public?void?onResume()?{????
????????super.onResume();????
??
????????IntentFilter?counterActionFilter?=?new?IntentFilter(CounterService.BROADCAST_COUNTER_ACTION);????
????????registerReceiver(counterActionReceiver,?counterActionFilter);????
????}???
??
????......??
??
}??
public class MainActivity extends Activity implements OnClickListener {
	......

	@Override
	public void onResume() {
		super.onResume();  

		IntentFilter counterActionFilter = new IntentFilter(CounterService.BROADCAST_COUNTER_ACTION);
		registerReceiver(counterActionReceiver, counterActionFilter);
	} 

	......

}
?? ? ? ?MainActivity在onResume函数里，通过其父类ContextWrapper的registerReceiver函数注册了一个BroadcastReceiver实例counterActionReceiver，并且通过IntentFilter实例counterActionFilter告诉ActivityManagerService，它要订阅的广播是CounterService.BROADCAST_COUNTER_ACTION类型的，这样，ActivityManagerService在收到CounterService.BROADCAST_COUNTER_ACTION类型的广播时，就会分发给counterActionReceiver实例的onReceive函数。
?? ? ? ?接下来，就开始分析注册过程中的每一个步骤了。
?? ? ? ?Step 1. ContextWrapper.registerReceiver
?? ? ? ?这个函数实现在frameworks/base/core/java/android/content/ContextWrapper.java文件中：
[java] view plain copy print ?
public?class?ContextWrapper?extends?Context?{??
????Context?mBase;??
????......??
??
????@Override??
????public?Intent?registerReceiver(??
????????BroadcastReceiver?receiver,?IntentFilter?filter)?{??
????????return?mBase.registerReceiver(receiver,?filter);??
????}??
??
????......??
??
}??
public class ContextWrapper extends Context {
	Context mBase;
	......

	@Override
	public Intent registerReceiver(
		BroadcastReceiver receiver, IntentFilter filter) {
		return mBase.registerReceiver(receiver, filter);
	}

	......

}
?? ? ? ?这里的成员变量mBase是一个ContextImpl实例，想知道为什么，可以回过头去看看Android应用程序启动过程源代码分析这篇文章>~<。
?? ? ? ?Step 2. ContextImpl.registerReceiver
?? ? ? ?这个函数实现在frameworks/base/core/java/android/app/ContextImpl.java文件中：
[java] view plain copy print ?
class?ContextImpl?extends?Context?{??
????......??
??
????@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,?filter,?broadcastPermission,??
????????????scheduler,?getOuterContext());??
????}??
??
????private?Intent?registerReceiverInternal(BroadcastReceiver?receiver,??
????????????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?{??
????????????????......??
????????????}??
????????}??
????????try?{??
????????????return?ActivityManagerNative.getDefault().registerReceiver(??
????????????????????mMainThread.getApplicationThread(),??
????????????????????rd,?filter,?broadcastPermission);??
????????}?catch?(RemoteException?e)?{??
????????????????return?null;??
????????}??
????}??
??
????......??
??
}??
class ContextImpl extends Context {
	......

	@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, filter, broadcastPermission,
			scheduler, getOuterContext());
	}

	private Intent registerReceiverInternal(BroadcastReceiver receiver,
			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 {
				......
			}
		}
		try {
			return ActivityManagerNative.getDefault().registerReceiver(
					mMainThread.getApplicationThread(),
					rd, filter, broadcastPermission);
		} catch (RemoteException e) {
				return null;
		}
	}

	......

}
?? ? ? ?通过两个函数的中转，最终就进入到ContextImpl.registerReceiverInternal这个函数来了。这里的成员变量mPackageInfo是一个LoadedApk实例，它是用来负责处理广播的接收的，在后面一篇文章讲到广播的发送时（sendBroadcast），会详细描述。参数broadcastPermission和scheduler都为null，而参数context是上面的函数通过调用函数getOuterContext得到的，这里它就是指向MainActivity了，因为MainActivity是继承于Context类的，因此，这里用Context类型来引用。
?? ? ? ?由于条件mPackageInfo != null和context != null都成立，而且条件scheduler == null也成立，于是就调用mMainThread.getHandler来获得一个Handler了，这个Hanlder是后面用来分发ActivityManagerService发送过的广播用的。这里的成员变量mMainThread是一个ActivityThread实例，在前面Android应用程序启动过程源代码分析这篇文章也描述过了。我们先来看看ActivityThread.getHandler函数的实现，然后再回过头来继续分析ContextImpl.registerReceiverInternal函数。
?? ? ? ?Step 3. ActivityThread.getHandler
?? ? ? ?这个函数实现在frameworks/base/core/java/android/app/ActivityThread.java文件中：
[java] view plain copy print ?
public?final?class?ActivityThread?{??
????......??
??
????final?H?mH?=?new?H();??
??
????private?final?class?H?extends?Handler?{??
????????......??
??
????????public?void?handleMessage(Message?msg)?{??
????????????......??
??
????????????switch?(msg.what)?{??
????????????......??
????????????}??
??
????????????......??
????????}??
??
????????......??
??
????}??
??
????......??
??
????final?Handler?getHandler()?{??
????????return?mH;??
????}??
??
????......??
??
}??
public final class ActivityThread {
	......

	final H mH = new H();

	private final class H extends Handler {
		......

		public void handleMessage(Message msg) {
			......

			switch (msg.what) {
			......
			}

			......
		}

		......

	}

	......

	final Handler getHandler() {
		return mH;
	}

	......

}
?? ? ? ?有了这个Handler之后，就可以分发消息给应用程序处理了。
?? ? ? ?再回到上一步的ContextImpl.registerReceiverInternal函数中，它通过mPackageInfo.getReceiverDispatcher函数获得一个IIntentReceiver接口对象rd，这是一个Binder对象，接下来会把它传给ActivityManagerService，ActivityManagerService在收到相应的广播时，就是通过这个Binder对象来通知MainActivity来接收的。
?? ? ? ?我们也是先来看一下mPackageInfo.getReceiverDispatcher函数的实现，然后再回过头来继续分析ContextImpl.registerReceiverInternal函数。
?? ? ? ?Step 4. LoadedApk.getReceiverDispatcher
?? ? ? ?这个函数实现在frameworks/base/core/java/android/app/LoadedApk.java文件中：
[java] view plain copy print ?
final?class?LoadedApk?{??
????......??
??
????public?IIntentReceiver?getReceiverDispatcher(BroadcastReceiver?r,??
????????????Context?context,?Handler?handler,??
????????????Instrumentation?instrumentation,?boolean?registered)?{??
????????synchronized?(mReceivers)?{??
????????????LoadedApk.ReceiverDispatcher?rd?=?null;??
????????????HashMap<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?HashMap<BroadcastReceiver,?LoadedApk.ReceiverDispatcher>();??
????????????????????????mReceivers.put(context,?map);??
????????????????????}??
????????????????????map.put(r,?rd);??
????????????????}??
????????????}?else?{??
????????????????rd.validate(context,?handler);??
????????????}??
????????????return?rd.getIIntentReceiver();??
????????}??
????}??
??
????......??
??
????static?final?class?ReceiverDispatcher?{??
??
????????final?static?class?InnerReceiver?extends?IIntentReceiver.Stub?{??
????????????final?WeakReference<LoadedApk.ReceiverDispatcher>?mDispatcher;??
????????????......??
??
????????????InnerReceiver(LoadedApk.ReceiverDispatcher?rd,?boolean?strong)?{??
????????????????mDispatcher?=?new?WeakReference<LoadedApk.ReceiverDispatcher>(rd);??
????????????????......??
????????????}??
??
????????????......??
????????}??
??
????????......??
??
????????final?IIntentReceiver.Stub?mIIntentReceiver;??
????????final?Handler?mActivityThread;??
??
????????......??
??
????????ReceiverDispatcher(BroadcastReceiver?receiver,?Context?context,??
????????????????Handler?activityThread,?Instrumentation?instrumentation,??
????????????????boolean?registered)?{??
????????????......??
??
????????????mIIntentReceiver?=?new?InnerReceiver(this,?!registered);??
????????????mActivityThread?=?activityThread;??
??????????????
????????????......??
????????}??
??
????????......??
??
????????IIntentReceiver?getIIntentReceiver()?{??
????????????return?mIIntentReceiver;??
????????}??
??
????}??
??
????......??
??
}??
final class LoadedApk {
	......

	public IIntentReceiver getReceiverDispatcher(BroadcastReceiver r,
			Context context, Handler handler,
			Instrumentation instrumentation, boolean registered) {
		synchronized (mReceivers) {
			LoadedApk.ReceiverDispatcher rd = null;
			HashMap<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 HashMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher>();
						mReceivers.put(context, map);
					}
					map.put(r, rd);
				}
			} else {
				rd.validate(context, handler);
			}
			return rd.getIIntentReceiver();
		}
	}

	......

	static final class ReceiverDispatcher {

		final static class InnerReceiver extends IIntentReceiver.Stub {
			final WeakReference<LoadedApk.ReceiverDispatcher> mDispatcher;
			......

			InnerReceiver(LoadedApk.ReceiverDispatcher rd, boolean strong) {
				mDispatcher = new WeakReference<LoadedApk.ReceiverDispatcher>(rd);
				......
			}

			......
		}

		......

		final IIntentReceiver.Stub mIIntentReceiver;
		final Handler mActivityThread;

		......

		ReceiverDispatcher(BroadcastReceiver receiver, Context context,
				Handler activityThread, Instrumentation instrumentation,
				boolean registered) {
			......

			mIIntentReceiver = new InnerReceiver(this, !registered);
			mActivityThread = activityThread;

			......
		}

		......

		IIntentReceiver getIIntentReceiver() {
			return mIIntentReceiver;
		}

	}

	......

}
?? ? ? ?在LoadedApk.getReceiverDispatcher函数中，首先看一下参数r是不是已经有相应的ReceiverDispatcher存在了，如果有，就直接返回了，否则就新建一个ReceiverDispatcher，并且以r为Key值保在一个HashMap中，而这个HashMap以Context，这里即为MainActivity为Key值保存在LoadedApk的成员变量mReceivers中，这样，只要给定一个Activity和BroadcastReceiver，就可以查看LoadedApk里面是否已经存在相应的广播接收发布器ReceiverDispatcher了。
?? ? ? ?在新建广播接收发布器ReceiverDispatcher时，会在构造函数里面创建一个InnerReceiver实例，这是一个Binder对象，实现了IIntentReceiver接口，可以通过ReceiverDispatcher.getIIntentReceiver函数来获得，获得后就会把它传给ActivityManagerService，以便接收广播。在ReceiverDispatcher类的构造函数中，还会把传进来的Handle类型的参数activityThread保存下来，以便后面在分发广播的时候使用。
?? ? ? ?现在，再回到ContextImpl.registerReceiverInternal函数，在获得了IIntentReceiver类型的Binder对象后，就开始要把它注册到ActivityManagerService中去了。
?? ? ? ?Step 5. ActivityManagerProxy.registerReceiver
?? ? ? ?这个函数实现在frameworks/base/core/java/android/app/ActivityManagerNative.java文件中：
[java] view plain copy print ?
class?ActivityManagerProxy?implements?IActivityManager??
{??
????......??
??
????public?Intent?registerReceiver(IApplicationThread?caller,??
????????????IIntentReceiver?receiver,??
????????????IntentFilter?filter,?String?perm)?throws?RemoteException??
????{??
????????Parcel?data?=?Parcel.obtain();??
????????Parcel?reply?=?Parcel.obtain();??
????????data.writeInterfaceToken(IActivityManager.descriptor);??
????????data.writeStrongBinder(caller?!=?null???caller.asBinder()?:?null);??
????????data.writeStrongBinder(receiver?!=?null???receiver.asBinder()?:?null);??
????????filter.writeToParcel(data,?0);??
????????data.writeString(perm);??
????????mRemote.transact(REGISTER_RECEIVER_TRANSACTION,?data,?reply,?0);??
????????reply.readException();??
????????Intent?intent?=?null;??
????????int?haveIntent?=?reply.readInt();??
????????if?(haveIntent?!=?0)?{??
????????????intent?=?Intent.CREATOR.createFromParcel(reply);??
????????}??
????????reply.recycle();??
????????data.recycle();??
????????return?intent;??
????}??
??
????......??
??
}??
class ActivityManagerProxy implements IActivityManager
{
	......

	public Intent registerReceiver(IApplicationThread caller,
			IIntentReceiver receiver,
			IntentFilter filter, String perm) throws RemoteException
	{
		Parcel data = Parcel.obtain();
		Parcel reply = Parcel.obtain();
		data.writeInterfaceToken(IActivityManager.descriptor);
		data.writeStrongBinder(caller != null ? caller.asBinder() : null);
		data.writeStrongBinder(receiver != null ? receiver.asBinder() : null);
		filter.writeToParcel(data, 0);
		data.writeString(perm);
		mRemote.transact(REGISTER_RECEIVER_TRANSACTION, data, reply, 0);
		reply.readException();
		Intent intent = null;
		int haveIntent = reply.readInt();
		if (haveIntent != 0) {
			intent = Intent.CREATOR.createFromParcel(reply);
		}
		reply.recycle();
		data.recycle();
		return intent;
	}

	......

}
?? ? ? ? 这个函数通过Binder驱动程序就进入到ActivityManagerService中的registerReceiver函数中去了。
?? ? ? ? Step 6. ActivityManagerService.registerReceiver
?? ? ? ? 这个函数实现在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中：
[java] view plain copy print ?
public?final?class?ActivityManagerService?extends?ActivityManagerNative??
????????implements?Watchdog.Monitor,?BatteryStatsImpl.BatteryCallback?{??
????......??
??
????public?Intent?registerReceiver(IApplicationThread?caller,??
????????????IIntentReceiver?receiver,?IntentFilter?filter,?String?permission)?{??
????????synchronized(this)?{??
????????????ProcessRecord?callerApp?=?null;??
????????????if?(caller?!=?null)?{??
????????????????callerApp?=?getRecordForAppLocked(caller);??
????????????????if?(callerApp?==?null)?{??
????????????????????......??
????????????????}??
????????????}??
??
????????????List?allSticky?=?null;??
??
????????????//?Look?for?any?matching?sticky?broadcasts...??
????????????Iterator?actions?=?filter.actionsIterator();??
????????????if?(actions?!=?null)?{??
????????????????while?(actions.hasNext())?{??
????????????????????String?action?=?(String)actions.next();??
????????????????????allSticky?=?getStickiesLocked(action,?filter,?allSticky);??
????????????????}??
????????????}?else?{??
????????????????......??
????????????}??
??
????????????//?The?first?sticky?in?the?list?is?returned?directly?back?to??
????????????//?the?client.??
????????????Intent?sticky?=?allSticky?!=?null???(Intent)allSticky.get(0)?:?null;??
??
????????????......??
??
????????????if?(receiver?==?null)?{??
????????????????return?sticky;??
????????????}??
??
????????????ReceiverList?rl??
????????????????=?(ReceiverList)mRegisteredReceivers.get(receiver.asBinder());??
????????????if?(rl?==?null)?{??
????????????????rl?=?new?ReceiverList(this,?callerApp,??
????????????????????Binder.getCallingPid(),??
????????????????????Binder.getCallingUid(),?receiver);??
??
????????????????if?(rl.app?!=?null)?{??
????????????????????rl.app.receivers.add(rl);??
????????????????}?else?{??
????????????????????......??
????????????????}??
????????????????mRegisteredReceivers.put(receiver.asBinder(),?rl);??
????????????}??
??
????????????BroadcastFilter?bf?=?new?BroadcastFilter(filter,?rl,?permission);??
????????????rl.add(bf);??
????????????......??
????????????mReceiverResolver.addFilter(bf);??
??
????????????//?Enqueue?broadcasts?for?all?existing?stickies?that?match??
????????????//?this?filter.??
????????????if?(allSticky?!=?null)?{??
????????????????......??
????????????}??
??
????????????return?sticky;??
????????}??
????}??
??
????......??
??
}??
public final class ActivityManagerService extends ActivityManagerNative
		implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
	......

	public Intent registerReceiver(IApplicationThread caller,
			IIntentReceiver receiver, IntentFilter filter, String permission) {
		synchronized(this) {
			ProcessRecord callerApp = null;
			if (caller != null) {
				callerApp = getRecordForAppLocked(caller);
				if (callerApp == null) {
					......
				}
			}

			List allSticky = null;

			// Look for any matching sticky broadcasts...
			Iterator actions = filter.actionsIterator();
			if (actions != null) {
				while (actions.hasNext()) {
					String action = (String)actions.next();
					allSticky = getStickiesLocked(action, filter, allSticky);
				}
			} else {
				......
			}

			// The first sticky in the list is returned directly back to
			// the client.
			Intent sticky = allSticky != null ? (Intent)allSticky.get(0) : null;

			......

			if (receiver == null) {
				return sticky;
			}

			ReceiverList rl
				= (ReceiverList)mRegisteredReceivers.get(receiver.asBinder());
			if (rl == null) {
				rl = new ReceiverList(this, callerApp,
					Binder.getCallingPid(),
					Binder.getCallingUid(), receiver);

				if (rl.app != null) {
					rl.app.receivers.add(rl);
				} else {
					......
				}
				mRegisteredReceivers.put(receiver.asBinder(), rl);
			}

			BroadcastFilter bf = new BroadcastFilter(filter, rl, permission);
			rl.add(bf);
			......
			mReceiverResolver.addFilter(bf);

			// Enqueue broadcasts for all existing stickies that match
			// this filter.
			if (allSticky != null) {
				......
			}

			return sticky;
		}
	}

	......

}
?? ? ? ? 函数首先是获得调用registerReceiver函数的应用程序进程记录块：
[java] view plain copy print ?
???ProcessRecord?callerApp?=?null;??
???if?(caller?!=?null)?{??
callerApp?=?getRecordForAppLocked(caller);??
if?(callerApp?==?null)?{??
????......??
???????}??
???}??
    ProcessRecord callerApp = null;
    if (caller != null) {
	callerApp = getRecordForAppLocked(caller);
	if (callerApp == null) {
	    ......
        }
    }
?? ? ? ?这里得到的便是上一篇文章Android系统中的广播（Broadcast）机制简要介绍和学习计划里面介绍的应用程序Broadcast的进程记录块了，MainActivity就是在里面启动起来的。
?? ? ? ?
[java] view plain copy print ?
???List?allSticky?=?null;??
??
???//?Look?for?any?matching?sticky?broadcasts...??
???Iterator?actions?=?filter.actionsIterator();??
???if?(actions?!=?null)?{??
while?(actions.hasNext())?{??
????String?action?=?(String)actions.next();??
????allSticky?=?getStickiesLocked(action,?filter,?allSticky);??
}??
???}?else?{??
......??
???}??
??
???//?The?first?sticky?in?the?list?is?returned?directly?back?to??
???//?the?client.??
???Intent?sticky?=?allSticky?!=?null???(Intent)allSticky.get(0)?:?null;??
    List allSticky = null;

    // Look for any matching sticky broadcasts...
    Iterator actions = filter.actionsIterator();
    if (actions != null) {
	while (actions.hasNext()) {
		String action = (String)actions.next();
		allSticky = getStickiesLocked(action, filter, allSticky);
	}
    } else {
	......
    }

    // The first sticky in the list is returned directly back to
    // the client.
    Intent sticky = allSticky != null ? (Intent)allSticky.get(0) : null;
?? ? ? ?这里传进来的filter只有一个action，就是前面描述的CounterService.BROADCAST_COUNTER_ACTION了，这里先通过getStickiesLocked函数查找一下有没有对应的sticky intent列表存在。什么是Sticky Intent呢？我们在最后一次调用sendStickyBroadcast函数来发送某个Action类型的广播时，系统会把代表这个广播的Intent保存下来，这样，后来调用registerReceiver来注册相同Action类型的广播接收器，就会得到这个最后发出的广播。这就是为什么叫做Sticky Intent了，这个最后发出的广播虽然被处理完了，但是仍然被粘住在ActivityManagerService中，以便下一个注册相应Action类型的广播接收器还能继承处理。
?? ? ? ?这里，假设我们不使用sendStickyBroadcast来发送CounterService.BROADCAST_COUNTER_ACTION类型的广播，于是，这里得到的allSticky和sticky都为null了。
?? ? ? ?继续往下看，这里传进来的receiver不为null，于是，继续往下执行：
[java] view plain copy print ?
???ReceiverList?rl??
=?(ReceiverList)mRegisteredReceivers.get(receiver.asBinder());??
???if?(rl?==?null)?{??
rl?=?new?ReceiverList(this,?callerApp,??
????Binder.getCallingPid(),??
????Binder.getCallingUid(),?receiver);??
??
if?(rl.app?!=?null)?{??
????rl.app.receivers.add(rl);??
}?else?{??
????......??
}??
mRegisteredReceivers.put(receiver.asBinder(),?rl);??
???}??
    ReceiverList rl
	= (ReceiverList)mRegisteredReceivers.get(receiver.asBinder());
    if (rl == null) {
	rl = new ReceiverList(this, callerApp,
		Binder.getCallingPid(),
		Binder.getCallingUid(), receiver);

	if (rl.app != null) {
		rl.app.receivers.add(rl);
	} else {
		......
	}
	mRegisteredReceivers.put(receiver.asBinder(), rl);
    }
?? ? ? ?这里其实就是把广播接收器receiver保存一个ReceiverList列表中，这个列表的宿主进程是rl.app，这里就是MainActivity所在的进程了，在ActivityManagerService中，用一个进程记录块来表示这个应用程序进程，它里面有一个列表receivers，专门用来保存这个进程注册的广播接收器。接着，又把这个ReceiverList列表以receiver为Key值保存在ActivityManagerService的成员变量mRegisteredReceivers中，这些都是为了方便在收到广播时，快速找到对应的广播接收器的。
?? ? ? ?再往下看：
[java] view plain copy print ?
BroadcastFilter?bf?=?new?BroadcastFilter(filter,?rl,?permission);??
rl.add(bf);??
......??
mReceiverResolver.addFilter(bf);??
    BroadcastFilter bf = new BroadcastFilter(filter, rl, permission);
    rl.add(bf);
    ......
    mReceiverResolver.addFilter(bf);
?? ? ? ?上面只是把广播接收器receiver保存起来了，但是还没有把它和filter关联起来，这里就创建一个BroadcastFilter来把广播接收器列表rl和filter关联起来，然后保存在ActivityManagerService中的成员变量mReceiverResolver中去。
?? ? ? ?这样，广播接收器注册的过程就介绍完了，比较简单，但是工作又比较琐碎，主要就是将广播接收器receiver及其要接收的广播类型filter保存在ActivityManagerService中，以便以后能够接收到相应的广播并进行处理，在下一篇文章，我们将详细分析这个过程，敬请关注。