文章转载至CSDN社区罗升阳的安卓之旅,原文地址:http://blog.csdn.net/luoshengyang/article/details/6744448
前面我们分析了Android应用程序注册广播接收器的过程,这个过程只完成了万里长征的第一步,接下来它还要等待 ActivityManagerService将广播分发过来。ActivityManagerService是如何得到广播并把它分发出去的呢?这就是 本文要介绍的广播发送过程了。
广播的发送过程比广播接收器的注册过程要复杂得多了,不过这个过程仍然是以ActivityManagerService为中心。广播的发送者将广播发 送到ActivityManagerService,ActivityManagerService接收到这个广播以后,就会在自己的注册中心查看有哪些 广播接收器订阅了该广播,然后把这个广播逐一发送到这些广播接收器中,但是ActivityManagerService并不等待广播接收器处理这些广播 就返回了,因此,广播的发送和处理是异步的。概括来说,广播的发送路径就是从发送者到ActivityManagerService,再从 ActivityManagerService到接收者,这中间的两个过程都是通过Binder进程间通信机制来完成的,因此,希望读者在继续阅读本文之 前,对Android系统的Binder进程间通信机制有所了解,具体可以参考Android进程间通信(IPC)机制Binder简要介绍和学习计划一文。
本文继续以Android系统中的广播(Broadcast)机制简要介绍和学习计划一文中所开发的应用程序为例子,并且结合上文Android应用程序注册广播接收器(registerReceiver)的过程分析的内容,一起来分析Android应用程序发送广播的过程。
回顾一下Android系统中的广播(Broadcast)机制简要介绍和学习计划一 文中所开发的应用程序的组织架构,MainActivity向ActivityManagerService注册了一个 CounterService.BROADCAST_COUNTER_ACTION类型的计数器服务广播接收器,计数器服务CounterService 在后台线程中启动了一个异步任务(AsyncTask),这个异步任务负责不断地增加计数,并且不断地将当前计数值通过广播的形式发送出去,以便 MainActivity可以将当前计数值在应用程序的界面线程中显示出来。
计数器服务CounterService发送广播的代码如下所示:
[java] view plaincopy
- public class CounterService extends Service implements ICounterService {
- ......
- public void startCounter(int initVal) {
- AsyncTask<Integer, Integer, Integer> task = new AsyncTask<Integer, Integer, Integer>() {
- @Override
- protected Integer doInBackground(Integer... vals) {
- ......
- }
- @Override
- protected void onProgressUpdate(Integer... values) {
- super.onProgressUpdate(values);
- int counter = values[0];
- Intent intent = new Intent(BROADCAST_COUNTER_ACTION);
- intent.putExtra(COUNTER_VALUE, counter);
- sendBroadcast(intent);
- }
- @Override
- protected void onPostExecute(Integer val) {
- ......
- }
- };
- task.execute(0);
- }
- ......
- }
在onProgressUpdate函数中,创建了一个BROADCAST_COUNTER_ACTION类型的Intent,并且在这里个 Intent中附加上当前的计数器值,然后通过CounterService类的成员函数sendBroadcast将这个Intent发送出去。 CounterService类继承了Service类,Service类又继承了ContextWrapper类,成员函数sendBroadcast 就是从ContextWrapper类继承下来的,因此,我们就从ContextWrapper类的sendBroadcast函数开始,分析广播发送的 过程。
在继承分析广播的发送过程前,我们先来看一下广播发送过程的序列图,然后按照这个序图中的步骤来一步一步分析整个过程。
Step 1. ContextWrapper.sendBroadcast
这个函数定义在frameworks/base/core/java/android/content/ContextWrapper.java文件中:
[java] view plaincopy
- public class ContextWrapper extends Context {
- Context mBase;
- ......
- @Override
- public void sendBroadcast(Intent intent) {
- mBase.sendBroadcast(intent);
- }
- ......
- }
这里的成员变量mBase是一个ContextImpl实例,这里只简单地调用ContextImpl.sendBroadcast进一行操作。
Step 2. ContextImpl.sendBroadcast
这个函数定义在frameworks/base/core/java/android/app/ContextImpl.java文件中:
[java] view plaincopy
- class ContextImpl extends Context {
- ......
- @Override
- public void sendBroadcast(Intent intent) {
- String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
- try {
- ActivityManagerNative.getDefault().broadcastIntent(
- mMainThread.getApplicationThread(), intent, resolvedType, null,
- Activity.RESULT_OK, null, null, null, false, false);
- } catch (RemoteException e) {
- }
- }
- ......
- }
这里的resolvedType表示这个Intent的MIME类型,我们没有设置这个Intent的MIME类型,因此,这里的 resolvedType为null。接下来就调用ActivityManagerService的远程接口ActivityManagerProxy把 这个广播发送给ActivityManagerService了。
Step 3. ActivityManagerProxy.broadcastIntent
这个函数定义在frameworks/base/core/java/android/app/ActivityManagerNative.java文件中:
[java] view plaincopy
- class ActivityManagerProxy implements IActivityManager
- {
- ......
- public int broadcastIntent(IApplicationThread caller,
- Intent intent, String resolvedType, IIntentReceiver resultTo,
- int resultCode, String resultData, Bundle map,
- String requiredPermission, boolean serialized,
- boolean sticky) throws RemoteException
- {
- Parcel data = Parcel.obtain();
- Parcel reply = Parcel.obtain();
- data.writeInterfaceToken(IActivityManager.descriptor);
- data.writeStrongBinder(caller != null ? caller.asBinder() : null);
- intent.writeToParcel(data, 0);
- data.writeString(resolvedType);
- data.writeStrongBinder(resultTo != null ? resultTo.asBinder() : null);
- data.writeInt(resultCode);
- data.writeString(resultData);
- data.writeBundle(map);
- data.writeString(requiredPermission);
- data.writeInt(serialized ? 1 : 0);
- data.writeInt(sticky ? 1 : 0);
- mRemote.transact(BROADCAST_INTENT_TRANSACTION, data, reply, 0);
- reply.readException();
- int res = reply.readInt();
- reply.recycle();
- data.recycle();
- return res;
- }
- ......
- }
这里的实现比较简单,把要传递的参数封装好,然后通过Binder驱动程序进入到ActivityManagerService的broadcastIntent函数中。
Step 4. ctivityManagerService.broadcastIntent
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- public final int broadcastIntent(IApplicationThread caller,
- Intent intent, String resolvedType, IIntentReceiver resultTo,
- int resultCode, String resultData, Bundle map,
- String requiredPermission, boolean serialized, boolean sticky) {
- 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, map, requiredPermission, serialized,
- sticky, callingPid, callingUid);
- Binder.restoreCallingIdentity(origId);
- return res;
- }
- }
- ......
- }
这里调用broadcastIntentLocked函数来进一步处理。
Step 5. ActivityManagerService.broadcastIntentLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- private final int broadcastIntentLocked(ProcessRecord callerApp,
- String callerPackage, Intent intent, String resolvedType,
- IIntentReceiver resultTo, int resultCode, String resultData,
- Bundle map, String requiredPermission,
- boolean ordered, boolean sticky, int callingPid, int callingUid) {
- intent = new Intent(intent);
- ......
- // Figure out who all will receive this broadcast.
- List receivers = null;
- List<BroadcastFilter> registeredReceivers = null;
- try {
- if (intent.getComponent() != null) {
- ......
- } else {
- ......
- registeredReceivers = mReceiverResolver.queryIntent(intent, resolvedType, false);
- }
- } catch (RemoteException ex) {
- ......
- }
- final boolean replacePending =
- (intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;
- 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.
- BroadcastRecord r = new BroadcastRecord(intent, callerApp,
- callerPackage, callingPid, callingUid, requiredPermission,
- registeredReceivers, resultTo, resultCode, resultData, map,
- ordered, sticky, false);
- ......
- boolean replaced = false;
- if (replacePending) {
- for (int i=mParallelBroadcasts.size()-1; i>=0; i--) {
- if (intent.filterEquals(mParallelBroadcasts.get(i).intent)) {
- ......
- mParallelBroadcasts.set(i, r);
- replaced = true;
- break;
- }
- }
- }
- if (!replaced) {
- mParallelBroadcasts.add(r);
- scheduleBroadcastsLocked();
- }
- registeredReceivers = null;
- NR = 0;
- }
- ......
- }
- ......
- }
这个函数首先是根据intent找出相应的广播接收器:
[java] view plaincopy
- // Figure out who all will receive this broadcast.
- List receivers = null;
- List<BroadcastFilter> registeredReceivers = null;
- try {
- if (intent.getComponent() != null) {
- ......
- } else {
- ......
- registeredReceivers = mReceiverResolver.queryIntent(intent, resolvedType, false);
- }
- } catch (RemoteException ex) {
- ......
- }
回忆一下前面一篇文章Android应用程序注册广播接收器(registerReceiver)的过程分析中 的Step 6(ActivityManagerService.registerReceiver)中,我们将一个filter类型为 BROADCAST_COUNTER_ACTION类型的BroadcastFilter实例保存在了ActivityManagerService的成 员变量mReceiverResolver中,这个BroadcastFilter实例包含了我们所注册的广播接收器,这里就通过 mReceiverResolver.queryIntent函数将这个BroadcastFilter实例取回来。由于注册一个广播类型的接收器可能有 多个,所以这里把所有符合条件的的BroadcastFilter实例放在一个List中,然后返回来。在我们这个场景中,这个List就只有一个 BroadcastFilter实例了,就是MainActivity注册的那个广播接收器。
继续往下看:
[java] view plaincopy
- final boolean replacePending =
- (intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;
这里是查看一下这个intent的Intent.FLAG_RECEIVER_REPLACE_PENDING位有没有设置,如果设置了的 话,ActivityManagerService就会在当前的系统中查看有没有相同的intent还未被处理,如果有的话,就有当前这个新的 intent来替换旧的intent。这里,我们没有设置intent的Intent.FLAG_RECEIVER_REPLACE_PENDING位, 因此,这里的replacePending变量为false。
再接着往下看:
[java] view plaincopy
- 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.
- BroadcastRecord r = new BroadcastRecord(intent, callerApp,
- callerPackage, callingPid, callingUid, requiredPermission,
- registeredReceivers, resultTo, resultCode, resultData, map,
- ordered, sticky, false);
- ......
- boolean replaced = false;
- if (replacePending) {
- for (int i=mParallelBroadcasts.size()-1; i>=0; i--) {
- if (intent.filterEquals(mParallelBroadcasts.get(i).intent)) {
- ......
- mParallelBroadcasts.set(i, r);
- replaced = true;
- break;
- }
- }
- }
- if (!replaced) {
- mParallelBroadcasts.add(r);
- scheduleBroadcastsLocked();
- }
- registeredReceivers = null;
- NR = 0;
- }
前面我们说到,这里得到的列表registeredReceivers的大小为1,且传进来的参数ordered为false,表示要将这个广播发送给 所有注册了BROADCAST_COUNTER_ACTION类型广播的接收器,因此,会执行下面的if语句。这个if语句首先创建一个广播记录块 BroadcastRecord,里面记录了这个广播是由谁发出的以及要发给谁等相关信息。由于前面得到的replacePending变量为 false,因此,不会执行接下来的if语句,即不会检查系统中是否有相同类型的未处理的广播。
这样,这里得到的replaced变量的值也为false,于是,就会把这个广播记录块r放在ActivityManagerService的成员变量 mParcelBroadcasts中,等待进一步处理;进一步处理的操作由函数scheduleBroadcastsLocked进行。
Step 6. ActivityManagerService.scheduleBroadcastsLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- private final void scheduleBroadcastsLocked() {
- ......
- if (mBroadcastsScheduled) {
- return;
- }
- mHandler.sendEmptyMessage(BROADCAST_INTENT_MSG);
- mBroadcastsScheduled = true;
- }
- ......
- }
这里的mBroadcastsScheduled表示ActivityManagerService当前是不是正在处理其它广播,如果是的话,这里就先不处理直接返回了,保证所有广播串行处理。
注意这里处理广播的方式,它是通过消息循环来处理,每当ActivityManagerService接收到一个广播时,它就把这个广播放进自己的消息队列去就完事了,根本不管这个广播后续是处理的,因此,这里我们可以看出广播的发送和处理是异步的。
这里的成员变量mHandler是一个在ActivityManagerService内部定义的Handler类变量,通过它的 sendEmptyMessage函数把一个类型为BROADCAST_INTENT_MSG的空消息放进ActivityManagerService 的消息队列中去。这里的空消息是指这个消息除了有类型信息之外,没有任何其它额外的信息,因为前面已经把要处理的广播信息都保存在 mParcelBroadcasts中了,等处理这个消息时,从mParcelBroadcasts就可以读回相关的广播信息了,因此,这里不需要把广播 信息再放在消息内容中。
Step 7. Handler.sendEmptyMessage
这个自定义的Handler类实现在frameworks/base/services/java/com/android/server/am /ActivityManagerService.java文件中,它是ActivityManagerService的内部类,调用了它的 sendEmptyMessage函数来把一个消息放到消息队列后,一会就会调用它的handleMessage函数来真正处理这个消息:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- final Handler mHandler = new Handler() {
- public void handleMessage(Message msg) {
- switch (msg.what) {
- ......
- case BROADCAST_INTENT_MSG: {
- ......
- processNextBroadcast(true);
- } break;
- ......
- }
- }
- }
- ......
- }
这里又调用了ActivityManagerService的processNextBroadcast函数来处理下一个未处理的广播。
Step 8. ActivityManagerService.processNextBroadcast
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- private final void processNextBroadcast(boolean fromMsg) {
- synchronized(this) {
- BroadcastRecord r;
- ......
- if (fromMsg) {
- mBroadcastsScheduled = false;
- }
- // First, deliver any non-serialized broadcasts right away.
- 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);
- ......
- deliverToRegisteredReceiverLocked(r, (BroadcastFilter)target, false);
- }
- addBroadcastToHistoryLocked(r);
- ......
- }
- ......
- }
- }
- ......
- }
这里传进来的参数fromMsg为true,于是把mBroadcastScheduled重新设为false,这样,下一个广播就能进入到消息队列中 进行处理了。前面我们在Step 5中,把一个广播记录块BroadcastRecord放在了mParallelBroadcasts中,因此,这里就把它取出来进行处理了。广播记录块 BroadcastRecord的receivers列表中包含了要接收这个广播的目标列表,即前面我们注册的广播接收器,用 BroadcastFilter来表示,这里while循环中的for循环就是把这个广播发送给每一个订阅了该广播的接收器了,通过 deliverToRegisteredReceiverLocked函数执行。
Step 9. ActivityManagerService.deliverToRegisteredReceiverLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- private final void deliverToRegisteredReceiverLocked(BroadcastRecord r,
- BroadcastFilter filter, boolean ordered) {
- boolean skip = false;
- if (filter.requiredPermission != null) {
- ......
- }
- if (r.requiredPermission != null) {
- ......
- }
- if (!skip) {
- // If this is not being sent as an ordered broadcast, then we
- // don‘t want to touch the fields that keep track of the current
- // state of ordered broadcasts.
- if (ordered) {
- ......
- }
- try {
- ......
- performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver,
- new Intent(r.intent), r.resultCode,
- r.resultData, r.resultExtras, r.ordered, r.initialSticky);
- ......
- } catch (RemoteException e) {
- ......
- }
- }
- }
- ......
- }
函数首先是检查一下广播发送和接收的权限,在我们分析的这个场景中,没有设置权限,因此,这个权限检查就跳过了,这里得到的skip为false,于是进 入下面的if语句中。由于上面传时来的ordered参数为false,因此,直接就调用performReceiveLocked函数来进一步执行广播 发送的操作了。
Step 10. ActivityManagerService.performReceiveLocked
这个函数定义在frameworks/base/services/java/com/android/server/am/ActivityManagerService.java文件中:
[java] view plaincopy
- public final class ActivityManagerService extends ActivityManagerNative
- implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
- ......
- static void performReceiveLocked(ProcessRecord app, IIntentReceiver receiver,
- Intent intent, int resultCode, String data, Bundle extras,
- boolean ordered, boolean sticky) throws RemoteException {
- // Send the intent to the receiver asynchronously using one-way binder calls.
- if (app != null && 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);
- } else {
- ......
- }
- }
- ......
- }
注意,这里传进来的参数app是注册广播接收器的Activity所在的进程记录块,在我们分析的这个场景中,由于是MainActivity调用 registerReceiver函数来注册这个广播接收器的,因此,参数app所代表的ProcessRecord就是MainActivity所在的 进程记录块了;而参数receiver也是注册广播接收器时传给ActivityManagerService的一个Binder对象,它的类型是 IIntentReceiver,具体可以参考上一篇文章Android应用程序注册广播接收器(registerReceiver)的过程分析中的Step 2。
MainActivity在注册广播接收器时,已经把自己的ProcessRecord记录下来了,所以这里的参数app和app.thread均不为 null,于是,ActivityManagerService就调用app.thread.scheduleRegisteredReceiver函数 来把这个广播分发给MainActivity了。这里的app.thread是一个Binder远程对象,它的类型是 ApplicationThreadProxy,我们在前面介绍应用程序的Activity启动过程时,已经多次看到了,具体可以参考主题Android应用程序的Activity启动过程简要介绍和学习计划。
Step 11. ApplicationThreadProxy.scheduleRegisteredReceiver
这个函数定义在frameworks/base/core/java/android/app/ApplicationThreadNative.java文件中:
[java] view plaincopy
- class ApplicationThreadProxy implements IApplicationThread {
- ......
- public void scheduleRegisteredReceiver(IIntentReceiver receiver, Intent intent,
- int resultCode, String dataStr, Bundle extras, boolean ordered, boolean sticky)
- throws RemoteException {
- Parcel data = Parcel.obtain();
- data.writeInterfaceToken(IApplicationThread.descriptor);
- data.writeStrongBinder(receiver.asBinder());
- intent.writeToParcel(data, 0);
- data.writeInt(resultCode);
- data.writeString(dataStr);
- data.writeBundle(extras);
- data.writeInt(ordered ? 1 : 0);
- data.writeInt(sticky ? 1 : 0);
- mRemote.transact(SCHEDULE_REGISTERED_RECEIVER_TRANSACTION, data, null,
- IBinder.FLAG_ONEWAY);
- data.recycle();
- }
- ......
- }
这里通过Binder驱动程序就进入到ApplicationThread.scheduleRegisteredReceiver函数去了。
ApplicationThread是ActivityThread的一个内部类,具体可以参考Activity启动主题Android应用程序的Activity启动过程简要介绍和学习计划。
Step 12. ApplicaitonThread.scheduleRegisteredReceiver
这个函数定义在frameworks/base/core/java/android/app/ActivityThread.java文件中:
[java] view plaincopy
- public final class ActivityThread {
- ......
- private final class ApplicationThread extends ApplicationThreadNative {
- ......
- // This function exists to make sure all receiver dispatching is
- // correctly ordered, since these are one-way calls and the binder driver
- // applies transaction ordering per object for such calls.
- public void scheduleRegisteredReceiver(IIntentReceiver receiver, Intent intent,
- int resultCode, String dataStr, Bundle extras, boolean ordered,
- boolean sticky) throws RemoteException {
- receiver.performReceive(intent, resultCode, dataStr, extras, ordered, sticky);
- }
- ......
- }
- ......
- }
这里的receiver是在前面一篇文章Android应用程序注册广播接收器(registerReceiver)的过程分析中
的Step
4中创建的,它的具体类型是LoadedApk.ReceiverDispatcher.InnerReceiver,即定义在LoadedApk类的内
部类ReceiverDispatcher里面的一个内部类InnerReceiver,这里调用它的performReceive函数。
Step 13. InnerReceiver.performReceive
这个函数定义在frameworks/base/core/java/android/app/LoadedApk.java文件中:
[java] view plaincopy
- final class LoadedApk {
- ......
- static final class ReceiverDispatcher {
- final static class InnerReceiver extends IIntentReceiver.Stub {
- ......
- public void performReceive(Intent intent, int resultCode,
- String data, Bundle extras, boolean ordered, boolean sticky) {
- LoadedApk.ReceiverDispatcher rd = mDispatcher.get();
- ......
- if (rd != null) {
- rd.performReceive(intent, resultCode, data, extras,
- ordered, sticky);
- } else {
- ......
- }
- }
- }
- ......
- }
- ......
- }
这里,它只是简单地调用ReceiverDispatcher的performReceive函数来进一步处理,这里的ReceiverDispatcher类是LoadedApk类里面的一个内部类。
Step 14. ReceiverDispatcher.performReceive
这个函数定义在frameworks/base/core/java/android/app/LoadedApk.java文件中:
[java] view plaincopy
- final class LoadedApk {
- ......
- static final class ReceiverDispatcher {
- ......
- public void performReceive(Intent intent, int resultCode,
- String data, Bundle extras, boolean ordered, boolean sticky) {
- ......
- Args args = new Args();
- args.mCurIntent = intent;
- args.mCurCode = resultCode;
- args.mCurData = data;
- args.mCurMap = extras;
- args.mCurOrdered = ordered;
- args.mCurSticky = sticky;
- if (!mActivityThread.post(args)) {
- ......
- }
- }
- ......
- }
- ......
- }
这里mActivityThread成员变量的类型为Handler,它是前面MainActivity注册广播接收器时,从ActivityThread取得的,具体可以参考前面一篇文章Android应用程序注册广播接收器(registerReceiver)的过程分析中
的Step
3。这里ReceiverDispatcher借助这个Handler,把这个广播以消息的形式放到MainActivity所在的这个
ActivityThread的消息队列中去,因此,ReceiverDispatcher不等这个广播被MainActivity处理就返回了,这里也
体现了广播的发送和处理是异步进行的。
注意这里处理消息的方式是通过Handler.post函数进行的,post函数的参数是Runnable类型的,这个消息最终会调用这个这个参数的
run成员函数来处理。这里的Args类是LoadedApk类的内部类ReceiverDispatcher的一个内部类,它继承于Runnable
类,因此,可以作为mActivityThread.post的参数传进去,代表这个广播的intent也保存在这个Args实例中。
Step 15. Hanlder.post
这个函数定义在frameworks/base/core/java/android/os/Handler.java文件中,这个函数我们就不看了,
有兴趣的读者可以自己研究一下,它的作用就是把消息放在消息队列中,然后就返回了,这个消息最终会在传进来的Runnable类型的参数的run成员函数
中进行处理。
Step 16. Args.run
这个函数定义在frameworks/base/core/java/android/app/LoadedApk.java文件中:
[java] view plaincopy
- final class LoadedApk {
- ......
- static final class ReceiverDispatcher {
- ......
- final class Args implements Runnable {
- ......
- public void run() {
- BroadcastReceiver receiver = mReceiver;
- ......
- Intent intent = mCurIntent;
- ......
- try {
- ClassLoader cl = mReceiver.getClass().getClassLoader();
- intent.setExtrasClassLoader(cl);
- if (mCurMap != null) {
- mCurMap.setClassLoader(cl);
- }
- receiver.setOrderedHint(true);
- receiver.setResult(mCurCode, mCurData, mCurMap);
- receiver.clearAbortBroadcast();
- receiver.setOrderedHint(mCurOrdered);
- receiver.setInitialStickyHint(mCurSticky);
- receiver.onReceive(mContext, intent);
- } catch (Exception e) {
- ......
- }
- ......
- }
- ......
- }
- ......
- }
- ......
- }
这里的mReceiver是ReceiverDispatcher类的成员变量,它的类型是BroadcastReceiver,这里它就是
MainActivity注册广播接收器时创建的BroadcastReceiver实例了,具体可以参考前面一篇文章Android应用程序注册广播接收器(registerReceiver)的过程分析中的Step 2。
有了这个ReceiverDispatcher实例之后,就可以调用它的onReceive函数把这个广播分发给它处理了。
Step 17. BroadcastReceiver.onReceive
这个函数定义Android系统中的广播(Broadcast)机制简要介绍和学习计划一文中所介绍的Android应用程序Broadcast的工程目录下的src/shy/luo/broadcast/MainActivity.java文件中:
[java] view plaincopy
- public class MainActivity extends Activity implements OnClickListener {
- ......
- private BroadcastReceiver counterActionReceiver = new BroadcastReceiver(){
- public void onReceive(Context context, Intent intent) {
- int counter = intent.getIntExtra(CounterService.COUNTER_VALUE, 0);
- String text = String.valueOf(counter);
- counterText.setText(text);
- Log.i(LOG_TAG, "Receive counter event");
- }
- }
- ......
- }
这样,MainActivity里面的定义的BroadcastReceiver实例counterActionReceiver就收到这个广播并进行处理了。
至此,Android应用程序发送广播的过程就分析完成了,结合前面这篇分析广播接收器注册过程的文章Android应用程序注册广播接收器(registerReceiver)的过程分析,就会对Android系统的广播机制且个更深刻的认识和理解了。
最后,我们总结一下这个Android应用程序发送广播的过程:
1. Step 1 - Step
7,计数器服务CounterService通过sendBroadcast把一个广播通过Binder进程间通信机制发送给
ActivityManagerService,ActivityManagerService根据这个广播的Action类型找到相应的广播接收器,然
后把这个广播放进自己的消息队列中去,就完成第一阶段对这个广播的异步分发了;
2. Step 8 - Step
15,ActivityManagerService在消息循环中处理这个广播,并通过Binder进程间通信机制把这个广播分发给注册的广播接收分发器
ReceiverDispatcher,ReceiverDispatcher把这个广播放进MainActivity所在的线程的消息队列中去,就完成
第二阶段对这个广播的异步分发了;
3. Step 16 - Step
17, ReceiverDispatcher的内部类Args在MainActivity所在的线程消息循环中处理这个广播,最终是将这个广播分发给所
注册的BroadcastReceiver实例的onReceive函数进行处理。
这样,Android系统广播机制就学习完成了,希望对读者有所帮助。重新学习Android系统的广播机制,请回到Android系统中的广播(Broadcast)机制简要介绍和学习计划一文中。
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