前言 我們接著來學(xué)習(xí)Android四大組件中的BroadcastReceiver，廣播主要就是分為注冊、接收和發(fā)送過程。建議閱讀此文前請先閱讀Android深入理解四大組件系列的文章，知識重復(fù)的部分，本文不再贅述。
1.廣播的注冊過程 BroadcastReceiver的注冊分為兩種，分別是靜態(tài)注冊和動態(tài)注冊，靜態(tài)注冊在應(yīng)用安裝時(shí)由PackageManagerService來完成注冊過程，關(guān)于這一過程，我會在后續(xù)的介紹PackageManagerService文章中詳細(xì)介紹。這里只介紹BroadcastReceiver的動態(tài)注冊。
frameworks/base/core/java/android/content/ContextWrapper.java
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) { return mBase.registerReceiver(receiver, filter);
} View Code 這里mBase具體指向就是ContextImpl，不明白的請查看Android深入四大組件（二）Service的啟動過程這篇文章。ContextImpl的registerReceiver方法有很多重載的方法最終會調(diào)用registerReceiverInternal方法：frameworks/base/core/java/android/app/ContextImpl.java
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 ) {
// 1 if (scheduler ==
null ) {scheduler =
mMainThread.getHandler();}rd =
mPackageInfo.getReceiverDispatcher(receiver, context, scheduler,mMainThread.getInstrumentation(), true );
// 2 }
else { if (scheduler ==
null ) {scheduler =
mMainThread.getHandler();}rd =
new LoadedApk.ReceiverDispatcher(receiver, context, scheduler, null ,
true ).getIIntentReceiver();
// 3
}} try {final Intent intent =
ActivityManagerNative.getDefault().registerReceiver(mMainThread.getApplicationThread(), mBasePackageName,rd, filter, broadcastPermission, userId); // 4 if (intent !=
null ) {intent.setExtrasClassLoader(getClassLoader());intent.prepareToEnterProcess();} return intent;} catch (RemoteException e) { throw e.rethrowFromSystemServer();} View Code 在注釋1處判斷如果LoadedApk類型的mPackageInfo不等于null并且context不等null就調(diào)用注釋2處的代碼通過mPackageInfo的getReceiverDispatcher方法獲取rd對象，否則就調(diào)用注釋3處的代碼來創(chuàng)建rd對象。注釋2和3的代碼的目的都是要獲取IIntentReceiver類型的rd對象，IIntentReceiver是一個(gè)Binder接口，用于進(jìn)行跨進(jìn)程的通信，它的具體實(shí)現(xiàn)在
frameworks/base/core/java/android/app/LoadedApk.java
static final
class ReceiverDispatcher {final static class InnerReceiver extends IIntentReceiver.Stub {final WeakReference <LoadedApk.ReceiverDispatcher>
mDispatcher;final LoadedApk.ReceiverDispatcher mStrongRef;InnerReceiver(LoadedApk.ReceiverDispatcher rd, boolean strong) {mDispatcher =
new WeakReference<LoadedApk.ReceiverDispatcher>
(rd);mStrongRef = strong ? rd :
null ;}... }... } View Code 回到registerReceiverInternal方法，在注釋4處調(diào)用了ActivityManagerProxy（AMP）的registerReceiver方法，最終會調(diào)用AMS的registerReceiver方法，并將rd傳就去。不明白的同學(xué)請查看Android深入四大組件（一）應(yīng)用程序啟動過程（前篇），這里不再贅述。frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public Intent registerReceiver(IApplicationThread caller, String callerPackage,IIntentReceiver receiver, IntentFilter filter, String permission, int userId) {
...synchronized( this ) {...Iterator <String> actions = filter.actionsIterator();
// 1
... // Collect stickies of users int [] userIds =
{ UserHandle.USER_ALL, UserHandle.getUserId(callingUid) }; while (actions.hasNext()) {String action =
actions.next(); for (
int id : userIds) {ArrayMap <String, ArrayList<Intent>> stickies = mStickyBroadcasts.
get (id); if (stickies !=
null ) {ArrayList <Intent> intents = stickies.
get (action); if (intents !=
null ) { if (stickyIntents ==
null ) {stickyIntents =
new ArrayList<Intent>
();}stickyIntents.addAll(intents); // 2
}}}}}ArrayList <Intent> allSticky =
null ; if (stickyIntents !=
null ) {final ContentResolver resolver =
mContext.getContentResolver(); for (
int i =
0 , N = stickyIntents.size(); i < N; i++
) {Intent intent = stickyIntents.
get (i); if (filter.match(resolver, intent,
true , TAG) >=
0 ) { if (allSticky ==
null ) {allSticky =
new ArrayList<Intent>
();}allSticky.add(intent); // 3
}}}...
} View Code 注釋1處根據(jù)傳入的IntentFilter類型的filter的得到actions列表，根據(jù)actions列表和userIds（userIds可以理解為應(yīng)用程序的uid）得到所有的粘性廣播的intent，并在注釋2處傳入到stickyIntents中，在注釋3處將這些粘性廣播的intent存入到allSticky列表中，從這里可以看出粘性廣播是存儲在AMS中的。frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
public Intent registerReceiver(IApplicationThread caller, String callerPackage,IIntentReceiver receiver, IntentFilter filter, String permission, int userId) {
...synchronized ( this ) {...ReceiverList rl = mRegisteredReceivers.
get (receiver.asBinder());
// 1 if (rl ==
null ) {rl =
new ReceiverList(
this , callerApp, callingPid, callingUid,userId, receiver); // 2 if (rl.app !=
null ) {rl.app.receivers.add(rl);} ...}...BroadcastFilter bf =
new BroadcastFilter(filter, rl, callerPackage,permission, callingUid, userId); // 3 rl.add(bf);
// 4 if (!
bf.debugCheck()) {Slog.w(TAG, " ==> For Dynamic broadcast " );}mReceiverResolver.addFilter(bf); // 5
... return sticky;}
} View Code 注釋1處獲取ReceiverList列表，如果為空則在注釋2處創(chuàng)建，ReceiverList繼承自ArrayList，用來存儲廣播接收者。在注釋3處創(chuàng)建BroadcastFilter并傳入此前創(chuàng)建的ReceiverList，BroadcastFilter用來描述注冊的廣播接收者，并在注釋4通過add方法將自身添加到ReceiverList中。注釋5處將BroadcastFilter添加到mReceiverResolver中，這樣當(dāng)AMS接收到廣播時(shí)就可以從mReceiverResolver中找到對應(yīng)的廣播接收者了。下面給出廣播的注冊過程的時(shí)序圖。
繪圖1_副本.png
2.廣播的發(fā)送和接收過程 ContextImpl到AMS的調(diào)用過程 廣播可以發(fā)送多種類型，包括無序廣播（普通廣播）、有序廣播和粘性廣播，這里以無序廣播為例，來講解廣播的發(fā)送過程。frameworks/base/core/java/android/content/ContextWrapper.java
@Override public void sendBroadcast(Intent intent) {mBase.sendBroadcast(intent);} View Code 接著來看ContextImpl中的sendBroadcast方法，如下所示。frameworks/base/core/java/android/app/ContextImpl.java
@Override public void sendBroadcast(Intent intent) {warnIfCallingFromSystemProcess();String resolvedType =
intent.resolveTypeIfNeeded(getContentResolver()); try {intent.prepareToLeaveProcess( this );ActivityManagerNative.getDefault().broadcastIntent(mMainThread.getApplicationThread(), intent, resolvedType, null ,Activity.RESULT_OK, null ,
null ,
null , AppOpsManager.OP_NONE,
null ,
false ,
false ,getUserId()); // 1 }
catch (RemoteException e) { throw e.rethrowFromSystemServer();}} View Code 注釋1處又是熟悉的代碼，最終會調(diào)用AMS的broadcastIntent方法：frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
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);
// 1
... /* ** 2 */ 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;}} View Code 我們來查看注釋1處的verifyBroadcastLocked方法：frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
final Intent verifyBroadcastLocked(Intent intent) { // Refuse possible leaked file descriptors if (intent !=
null && intent.hasFileDescriptors() ==
true ) {
// 1 throw new IllegalArgumentException(
" File descriptors passed in Intent " );} int flags = intent.getFlags();
// 2 if (!
mProcessesReady) { if ((flags&Intent.FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT) !=
0 ) {
// 3 }
else if ((flags&Intent.FLAG_RECEIVER_REGISTERED_ONLY) ==
0 ) {
// 4 Slog.e(TAG,
" Attempt to launch receivers of broadcast intent " +
intent +
" before boot completion " ); throw new IllegalStateException(
" Cannot broadcast before boot completed " );}} if ((flags&Intent.FLAG_RECEIVER_BOOT_UPGRADE) !=
0 ) { throw new IllegalArgumentException( " Can't use FLAG_RECEIVER_BOOT_UPGRADE here " );} return intent;} View Code verifyBroadcastLocked方法主要是驗(yàn)證廣播是否合法，在注釋1處驗(yàn)證intent是否不為null并且有文件描述符。注釋2處獲得intent中的flag。注釋3處如果系統(tǒng)正在啟動過程中，判斷如果flag設(shè)置為FLAG_RECEIVER_REGISTERED_ONLY_BEFORE_BOOT（啟動檢查時(shí)只接受動態(tài)注冊的廣播接收者）則不做處理，如果不是則在注釋4處判斷如果flag沒有設(shè)置為FLAG_RECEIVER_REGISTERED_ONLY（只接受動態(tài)注冊的廣播接收者）則會拋出異常。frameworks/base/services/core/java/com/android/server/am/ActivityManagerService.java
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) {... if ((receivers !=
null && receivers.size() >
0 ) || resultTo !=
null ) {BroadcastQueue queue =
broadcastQueueForIntent(intent); /* ** 1 */ BroadcastRecord r =
new BroadcastRecord(queue, intent, callerApp,callerPackage, callingPid, callingUid, resolvedType,requiredPermissions, appOp, brOptions, receivers, resultTo, resultCode,resultData, resultExtras, ordered, sticky, false , userId);... boolean replaced = replacePending &&
queue.replaceOrderedBroadcastLocked(r); if (!
replaced) {queue.enqueueOrderedBroadcastLocked(r);queue.scheduleBroadcastsLocked(); // 2
}} ...} return Act
View Code 這里省略了很多代碼，前面的工作主要是將動態(tài)注冊的廣播接收者和靜態(tài)注冊的廣播接收者按照優(yōu)先級高低存儲在不同的列表中，再將這兩個(gè)列表合并到receivers列表中，這樣receivers列表包含了所有的廣播接收者（無序廣播和有序廣播）。在注釋1處創(chuàng)建BroadcastRecord對象并將receivers傳進(jìn)去，在注釋2處調(diào)用BroadcastQueue的scheduleBroadcastsLocked方法。
繪圖8_副本.png
AMS到BroadcastReceiver的調(diào)用過程 BroadcastQueue的scheduleBroadcastsLocked方法的代碼如下所示。frameworks/base/services/core/java/com/android/server/am/BroadcastQueue.java
public void scheduleBroadcastsLocked() {
...mHandler.sendMessage(mHandler.obtainMessage(BROADCAST_INTENT_MSG, this ));
// 1 mBroadcastsScheduled =
true ;
} View Code 在注釋1處向BroadcastHandler類型的mHandler對象發(fā)送了BROADCAST_INTENT_MSG類型的消息，這個(gè)消息在BroadcastHandler的handleMessage方法中進(jìn)行處理，如下所示。frameworks/base/services/core/java/com/android/server/am/BroadcastQueue.java
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 ;...}}
} View Code 在handleMessage方法中調(diào)用了processNextBroadcast方法，processNextBroadcast方法對無序廣播和有序廣播分別進(jìn)行處理，旨在將廣播發(fā)送給廣播接收者，下面給出processNextBroadcast方法中對無序廣播的處理部分。frameworks/base/services/core/java/com/android/server/am/BroadcastQueue.java
final
void processNextBroadcast(boolean fromMsg) {
... if (fromMsg) {mBroadcastsScheduled =
false ;
// 1
} // First, deliver any non-serialized broadcasts right away. while (mParallelBroadcasts.size() >
0 ) {
// 2 r = mParallelBroadcasts.remove(
0 );
// 3
... for (
int i=
0 ; i<N; 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 , i);
// 4
}...}
} View Code 從前面的代碼我們得知fromMsg的值為true，因此注釋1處會將mBroadcastsScheduled 設(shè)置為flase，表示對于此前發(fā)來的BROADCAST_INTENT_MSG類型的消息已經(jīng)處理了。注釋2處的mParallelBroadcasts列表用來存儲無序廣播，通過while循環(huán)將mParallelBroadcasts列表中的無序廣播發(fā)送給對應(yīng)的廣播接收者。在注釋3處獲取每一個(gè)mParallelBroadcasts列表中存儲的BroadcastRecord類型的r對象。注釋4處將這些r對象描述的廣播發(fā)送給對應(yīng)的廣播接收者，deliverToRegisteredReceiverLocked方法如下所示。frameworks/base/services/core/java/com/android/server/am/BroadcastQueue.java
private void deliverToRegisteredReceiverLocked(BroadcastRecord r,BroadcastFilter filter, boolean ordered, int index) {
... try { if (DEBUG_BROADCAST_LIGHT) Slog.i(TAG_BROADCAST, " Delivering to " + filter +
" : " +
r); if (filter.receiverList.app !=
null &&
filter.receiverList.app.inFullBackup) {... } else {performReceiveLocked(filter.receiverList.app, filter.receiverList.receiver, new Intent(r.intent), r.resultCode, r.resultData,r.resultExtras, r.ordered, r.initialSticky, r.userId); // 1
} if (ordered) {r.state =
BroadcastRecord.CALL_DONE_RECEIVE;}} catch (RemoteException e) {...}} View Code 這里省去了大部分的代碼，這些代碼是用來檢查廣播發(fā)送者和廣播接收者的權(quán)限。如果通過了權(quán)限的檢查，則會調(diào)用注釋1處的performReceiveLocked方法：frameworks/base/services/core/java/com/android/server/am/BroadcastQueue.java
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 ) {
// 1 if (app.thread !=
null ) {
// 2 // 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); // 3
} } ...} else {receiver.performReceive(intent, resultCode, data, extras, ordered,sticky, sendingUser); /
}} View Code 注釋1和2處的代碼表示如果廣播接收者所在的應(yīng)用程序進(jìn)程存在并且正在運(yùn)行，則執(zhí)行注釋3處的代碼，表示用廣播接收者所在的應(yīng)用程序進(jìn)程來接收廣播，這里app.thread指的是ApplicationThread，我們來查看ApplicationThread的scheduleRegisteredReceiver方法，代碼如下所示。frameworks/base/core/java/android/app/ActivityThread.java
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); // 1 }
View Code 注釋1處調(diào)用了IIntentReceiver類型的對象receiver的performReceive方法，這里實(shí)現(xiàn)receiver的類為LoadedApk.ReceiverDispatcher.InnerReceiver，代碼如下所示。frameworks/base/core/java/android/app/LoadedApk.java
static final
class ReceiverDispatcher {final static class InnerReceiver extends IIntentReceiver.Stub {...InnerReceiver(LoadedApk.ReceiverDispatcher rd, boolean strong) {mDispatcher =
new WeakReference<LoadedApk.ReceiverDispatcher>
(rd);mStrongRef = strong ? rd :
null ;}@Override public void performReceive(Intent intent,
int resultCode, String data,Bundle extras, boolean ordered, boolean sticky, int sendingUser) {final LoadedApk.ReceiverDispatcher rd;... if (rd !=
null ) {rd.performReceive(intent, resultCode, data, extras,ordered, sticky, sendingUser); // 1 }
else {...}
...
} View Code 在注釋1處調(diào)用了ReceiverDispatcher類型的rd對象的performReceive方法：frameworks/base/core/java/android/app/LoadedApk.java
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); // 1
... if (intent ==
null || !mActivityThread.post(args)) {
// 2 if (mRegistered &&
ordered) {IActivityManager mgr =
ActivityManagerNative.getDefault(); if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG, " Finishing sync broadcast to " +
mReceiver);args.sendFinished(mgr);}} View Code 在注釋1處將廣播的intent等信息封裝為Args對象，并在注釋2處調(diào)用mActivityThread的post方法并傳入了Args對象。這個(gè)mActivityThread是一個(gè)Handler對象，具體指向的就是H，注釋2處的代碼就是將Args對象通過H發(fā)送到主線程的消息隊(duì)列中。Args繼承自Runnable，這個(gè)消息最終會在Args的run方法執(zhí)行，Args的run方法如下所示。
frameworks/base/core/java/android/app/LoadedApk.java
public void run() {... try {ClassLoader cl =
mReceiver.getClass().getClassLoader();intent.setExtrasClassLoader(cl);intent.prepareToEnterProcess();setExtrasClassLoader(cl);receiver.setPendingResult( this );receiver.onReceive(mContext, intent); // 1 }
catch (Exception e) {...}...} View Code 在注釋1處執(zhí)行了廣播接收者的onReceive方法，這樣注冊的廣播接收者就收到了廣播并得到了intent。
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轉(zhuǎn)載于:https://www.cnblogs.com/ganchuanpu/p/8597397.html
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