接上篇文章，這篇文章主要是總結(jié)前面知識(shí)，并且了解一些細(xì)節(jié)問(wèn)題，加深對(duì)廣播機(jī)制的理解，比如有播有序是怎么保證有序的？廣播攔截機(jī)制是怎么實(shí)現(xiàn)的？廣播發(fā)送超時(shí)了是怎么處理的？registerReceiver方法發(fā)返回值有什么用？粘性廣播等等。
Android源碼解析四大組件系列（五）---廣播的注冊(cè)過(guò)程
Android源碼解析四大組件系列（六）---廣播的處理過(guò)程
Android源碼解析四大組件系列（七）---廣播的發(fā)送過(guò)程
1、廣播相關(guān)數(shù)據(jù)結(jié)構(gòu)的再次理解
ReceiverDispatcher: 客戶端廣播分發(fā)者對(duì)象，第一篇講的很清楚了，ReceiverDispatcher的內(nèi)部類InnerReceiver為binder對(duì)象，用于與AMS的傳遞與通信。
ReceiverList: 繼承自ArrayList，存放了Receiver的binder對(duì)象以及其注冊(cè)的BroadcastFilter列表。AMS中定義了
final HashMap<IBinder, ReceiverList> mRegisteredReceivers = new HashMap<>();key為InnerReceiver的binder對(duì)象，值為ReceiverList，ReceiverList內(nèi)部記錄的是動(dòng)態(tài)注冊(cè)的廣播接收者，mRegisteredReceivers只有動(dòng)態(tài)注冊(cè)的時(shí)候才會(huì)有內(nèi)容。BroadcastFilter: 封裝了IntentFilter，描述動(dòng)態(tài)廣播，是動(dòng)態(tài)廣播節(jié)點(diǎn)。
ResolveInfo:Parcelable子類，描述靜態(tài)廣播，是靜態(tài)廣播節(jié)點(diǎn)。
IntentResolver: 解析Intent，在addFilter時(shí)即進(jìn)行解析。其內(nèi)部有mSchemeToFilter，mActionToFilter，mTypedActionToFilter三個(gè)map對(duì)象。key為對(duì)應(yīng)的action（scheme或者type），value為Filter。
BroadcastRecord:描述一個(gè)廣播， 將intent等一堆信息，封裝成BroadcastRecord，交給BroadcastQueue進(jìn)行處理。
BroadcastQueue: BroadcastQueue為Broadcast處理隊(duì)列，分為前臺(tái)隊(duì)列mFgBroadcastQueue和后臺(tái)隊(duì)列mBgBroadcastQueue，mFgBroadcastQueue會(huì)有更高的權(quán)限，被優(yōu)先處理。mFgBroadcastQueue和mBgBroadcastQueue兩個(gè)隊(duì)列中都含有mOrderedBroadcasts和mParallelBroadcasts兩個(gè)列表用來(lái)表示有序廣播列表和無(wú)序廣播列表。
２、有序廣播是怎么保證有序的
上一篇文章中說(shuō)了processNextBroadcast()只會(huì)處理一個(gè)BroadcastRecord的一個(gè)receiver，那怎么將廣播傳遞給下一個(gè)receiver呢？廣播接受者有“動(dòng)態(tài)”和“靜態(tài)”之分，廣播消息也有“串行”和“并行”之分，或者叫“有序”和“無(wú)序”之分。廣播的處理方式跟廣播的接收者和廣播消息類型有關(guān)系。有序廣播是怎么保證有序的這個(gè)問(wèn)題，得分情況討論，對(duì)于動(dòng)態(tài)注冊(cè)的receiver，先回到最終onReceive回調(diào)的地方，分析如下：
static final class ReceiverDispatcher {
.....
final class Args extends BroadcastReceiver.PendingResult implements Runnable {
.....
public Args(Intent intent, int resultCode, String resultData, Bundle resultExtras,
boolean ordered, boolean sticky, int sendingUser) {
//mRegistered傳進(jìn)來(lái)的是true
super(resultCode, resultData, resultExtras,
mRegistered ? TYPE_REGISTERED : TYPE_UNREGISTERED, ordered,
sticky, mIIntentReceiver.asBinder(), sendingUser, intent.getFlags());
mCurIntent = intent;
mOrdered = ordered;
}
public void run() {
.....
try {
ClassLoader cl = mReceiver.getClass().getClassLoader();
intent.setExtrasClassLoader(cl);
intent.prepareToEnterProcess();
setExtrasClassLoader(cl);
receiver.setPendingResult(this);
//廣播的onReceive方法回調(diào)
receiver.onReceive(mContext, intent);
} catch (Exception e) {
if (mRegistered && ordered) {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing failed broadcast to " + mReceiver);
sendFinished(mgr);
}
if (mInstrumentation == null ||
!mInstrumentation.onException(mReceiver, e)) {
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
throw new RuntimeException(
"Error receiving broadcast " + intent
+ " in " + mReceiver, e);
}
}
if (receiver.getPendingResult() != null) {
finish();
}
Trace.traceEnd(Trace.TRACE_TAG_ACTIVITY_MANAGER);
}
}
}
因?yàn)樵谡{(diào)用onReceive之前，執(zhí)行了 receiver.setPendingResult(this)，所以在下面receiver.getPendingResult()就不是null,則就進(jìn)入BroadcastReceiver的內(nèi)部類PendingResult的finish方法。
public final void finish() {
if (mType == TYPE_COMPONENT) {
final IActivityManager mgr = ActivityManagerNative.getDefault();
if (QueuedWork.hasPendingWork()) {
......
QueuedWork.singleThreadExecutor().execute( new Runnable() {
@Override public void run() {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast after work to component " + mToken);
sendFinished(mgr);
}
});
} else {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to component " + mToken);
sendFinished(mgr);
}
} else if (mOrderedHint && mType != TYPE_UNREGISTERED) {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to " + mToken);
final IActivityManager mgr = ActivityManagerNative.getDefault();
sendFinished(mgr);
}
}
finish方法中根據(jù)mType的值有兩個(gè)分支。mType是PendingResult的成員變量，在PendingResult的構(gòu)造函數(shù)中進(jìn)行賦值的。
public PendingResult(int resultCode, String resultData, Bundle resultExtras, int type,
boolean ordered, boolean sticky, IBinder token, int userId, int flags) {
mResultCode = resultCode;
mResultData = resultData;
mResultExtras = resultExtras;
mType = type;
mOrderedHint = ordered;
mInitialStickyHint = sticky;
mToken = token;
mSendingUser = userId;
mFlags = flags;
}
這個(gè)構(gòu)造方法是在BroadcastReceiver.PendingResult的子類Args中調(diào)用的
final class Args extends BroadcastReceiver.PendingResult implements Runnable {
private Intent mCurIntent;
private final boolean mOrdered;
private boolean mDispatched;
public Args(Intent intent, int resultCode, String resultData, Bundle resultExtras,
boolean ordered, boolean sticky, int sendingUser) {
super(resultCode, resultData, resultExtras,
mRegistered ? TYPE_REGISTERED : TYPE_UNREGISTERED, ordered,
sticky, mIIntentReceiver.asBinder(), sendingUser, intent.getFlags());
mCurIntent = intent;
mOrdered = ordered;
}
}
由于mRegistered是動(dòng)態(tài)注冊(cè)廣播接收者傳進(jìn)來(lái)的，值是true,所以上面mType的值是TYPE_REGISTERED，由于是有序廣播ordered值是true，那么mOrderedHint為true,所以要走第二個(gè)分支：
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to " + mToken);
final IActivityManager mgr = ActivityManagerNative.getDefault();
sendFinished(mgr);
BroadcastReceiver的sendFinished方法如下：
public void sendFinished(IActivityManager am) {
synchronized (this) {
if (mFinished) {
throw new IllegalStateException("Broadcast already finished");
}
mFinished = true;
try {
if (mResultExtras != null) {
mResultExtras.setAllowFds(false);
}
if (mOrderedHint) {
am.finishReceiver(mToken, mResultCode, mResultData, mResultExtras,
mAbortBroadcast, mFlags);
} else {
// This broadcast was sent to a component; it is not ordered,
// but we still need to tell the activity manager we are done.
am.finishReceiver(mToken, 0, null, null, false, mFlags);
}
} catch (RemoteException ex) {
}
}
}
有序廣播mOrderedHint值為true,所以進(jìn)入到AMS的finishReceiver方法。
public void finishReceiver(IBinder who, int resultCode, String resultData,
Bundle resultExtras, boolean resultAbort, int flags) {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST, "Finish receiver: " + who);
// Refuse possible leaked file descriptors
if (resultExtras != null && resultExtras.hasFileDescriptors()) {
throw new IllegalArgumentException("File descriptors passed in Bundle");
}
final long origId = Binder.clearCallingIdentity();
try {
boolean doNext = false;
BroadcastRecord r;
synchronized(this) {
BroadcastQueue queue = (flags & Intent.FLAG_RECEIVER_FOREGROUND) != 0
? mFgBroadcastQueue : mBgBroadcastQueue;
r = queue.getMatchingOrderedReceiver(who);
if (r != null) {
doNext = r.queue.finishReceiverLocked(r, resultCode,
resultData, resultExtras, resultAbort, true);
}
}
if (doNext) {
//再次執(zhí)行processNextBroadcast處理廣播
r.queue.processNextBroadcast(false);
}
trimApplications();
} finally {
Binder.restoreCallingIdentity(origId);
}
}
上面是分析了動(dòng)態(tài)的廣播接收者是怎么按照一個(gè)接著一個(gè)處理的。在看看靜態(tài)注冊(cè)的receiver，回到靜態(tài)廣播回調(diào)onReceive方法的地方。
private void handleReceiver(ReceiverData data) {
....
IActivityManager mgr = ActivityManagerNative.getDefault();
BroadcastReceiver receiver;
try {
java.lang.ClassLoader cl = packageInfo.getClassLoader();
data.intent.setExtrasClassLoader(cl);
data.intent.prepareToEnterProcess();
data.setExtrasClassLoader(cl);
//反射出BroadcastReceiver
receiver = (BroadcastReceiver)cl.loadClass(component).newInstance();
} catch (Exception e) {
....
}
try {
Application app = packageInfo.makeApplication(false, mInstrumentation);
....
ContextImpl context = (ContextImpl)app.getBaseContext();
sCurrentBroadcastIntent.set(data.intent);
receiver.setPendingResult(data);
//回調(diào)廣播的onReceive方法
receiver.onReceive(context.getReceiverRestrictedContext(),data.intent);
} catch (Exception e) {
....
}
} finally {
sCurrentBroadcastIntent.set(null);
}
if (receiver.getPendingResult() != null) {
data.finish();
}
}
在回調(diào)onReceiver方法之前， 執(zhí)行了 receiver.setPendingResult(data)，所以下面receiver.getPendingResult() != null成立，走 data.finish()，data是ReceiverData對(duì)象，handleReceiver方法傳進(jìn)來(lái)的，在scheduleReceiver方法中初始化。
public final void scheduleReceiver(Intent intent, ActivityInfo info,
CompatibilityInfo compatInfo, int resultCode, String data, Bundle extras,
boolean sync, int sendingUser, int processState) {
updateProcessState(processState, false);
ReceiverData r = new ReceiverData(intent, resultCode, data, extras,
sync, false, mAppThread.asBinder(), sendingUser);
r.info = info;
r.compatInfo = compatInfo;
sendMessage(H.RECEIVER, r);
}
我們看 data.finish()方法
public final void finish() {
if (mType == TYPE_COMPONENT) {
final IActivityManager mgr = ActivityManagerNative.getDefault();
if (QueuedWork.hasPendingWork()) {
QueuedWork.singleThreadExecutor().execute( new Runnable() {
@Override public void run() {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast after work to component " + mToken);
sendFinished(mgr);
}
});
} else {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to component " + mToken);
sendFinished(mgr);
}
} else if (mOrderedHint && mType != TYPE_UNREGISTERED) {
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to " + mToken);
final IActivityManager mgr = ActivityManagerNative.getDefault();
sendFinished(mgr);
}
}
此時(shí)mType分析后值是TYPE_COMPONENT，同樣會(huì)走sendFinished，后面AMS的處理邏輯是一樣的，不贅述。
３、廣播超時(shí)是怎么處理的?
AMS維護(hù)了兩個(gè)廣播隊(duì)列BroadcastQueue，mFgBroadcastQueue，前臺(tái)隊(duì)列的超時(shí)時(shí)間是10秒，mBgBroadcastQueue，后臺(tái)隊(duì)列的超時(shí)時(shí)間是60秒，如果廣播沒(méi)有在規(guī)定的時(shí)間內(nèi)處理完就會(huì)發(fā)生ANR,如果你想你的廣播進(jìn)入前臺(tái)廣播隊(duì)列，那么在發(fā)送的時(shí)候，在intent中加入Intent.FLAG_RECEIVER_FOREGROUND標(biāo)記，如果不加，系統(tǒng)默認(rèn)是后臺(tái)廣播。mFgBroadcastQueue會(huì)有更高的權(quán)限，被優(yōu)先處理。
在processNextBroadcast方法中有下面一段代碼，與廣播超時(shí)有關(guān)系，一旦超時(shí)就會(huì)出現(xiàn)ANR。
do {
int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;
if (mService.mProcessesReady && r.dispatchTime > 0) {
long now = SystemClock.uptimeMillis();
//廣播消息的第一個(gè)ANR監(jiān)測(cè)機(jī)制
if ((numReceivers > 0) &&
(now > r.dispatchTime + (2*mTimeoutPeriod*numReceivers))) {
Slog.w(TAG, "Hung broadcast ["
+ mQueueName + "] discarded after timeout failure:"
+ " now=" + now
+ " dispatchTime=" + r.dispatchTime
+ " startTime=" + r.receiverTime
+ " intent=" + r.intent
+ " numReceivers=" + numReceivers
+ " nextReceiver=" + r.nextReceiver
+ " state=" + r.state);
broadcastTimeoutLocked(false); // 超時(shí)處理
forceReceive = true;
r.state = BroadcastRecord.IDLE;
}
}
//判斷廣播有沒(méi)有處理完畢
if (r.receivers == null || r.nextReceiver >= numReceivers
|| r.resultAbort || forceReceive) {
// No more receivers for this broadcast! Send the final
// result if requested...
if (r.resultTo != null) {
try {
performReceiveLocked(r.callerApp, r.resultTo, new Intent(r.intent), r.resultCode r.resultData, r.resultExtras, false, false, r.userId);
r.resultTo = null;
} catch (RemoteException e) {
......
}
}
} while (r == null);
廣播的超時(shí)機(jī)制是針對(duì)有序廣播來(lái)說(shuō)的，無(wú)序廣播一次性全部處理了，肯定不會(huì)超時(shí)，超時(shí)的這段邏輯都在broadcastTimeoutLocked中，首先判斷是否超時(shí)，公式：r.dispatchTime + 2×mTimeoutPeriod×numReceivers，現(xiàn)在解釋一下這幾個(gè)時(shí)間：
dispatchTime的意義是標(biāo)記實(shí)際處理BroadcastRecord的起始時(shí)間，有序廣播是一個(gè)接著一個(gè)進(jìn)行處理的，第一次dispatchTime=0,并不會(huì)進(jìn)入該條件判斷
mTimeoutPeriod由當(dāng)前BroadcastQueue的類型決定(mFgBroadcastQueue為10秒，mBgBroadcastQueue為60秒)
// How long we allow a receiver to run before giving up on it.
static final int BROADCAST_FG_TIMEOUT = 10*1000;
static final int BROADCAST_BG_TIMEOUT = 60*1000;
mFgBroadcastQueue = new BroadcastQueue(this, mHandler, "foreground", BROADCAST_FG_TIMEOUT, false);
mBgBroadcastQueue = new BroadcastQueue(this, mHandler, "background", BROADCAST_BG_TIMEOUT, true);
所以上面公式翻譯過(guò)來(lái)就是：實(shí)際處理BroadcastRecord的起始時(shí)間＋廣播默認(rèn)的超時(shí)時(shí)間*廣播接收者的數(shù)量。話說(shuō)回來(lái)，這個(gè)公式為什么要這么設(shè)計(jì)呢？如果一個(gè)前臺(tái)的廣播消息有兩個(gè)接收者，那么在２0秒（２ x 10）之內(nèi)搞定就可以了，也可能第一個(gè)消息執(zhí)行了15秒，第二個(gè)消息執(zhí)行４.99秒，即使第一消息超過(guò)了10秒的規(guī)定，也不會(huì)出現(xiàn)ＡＮＲ。但是系統(tǒng)任務(wù)繁忙，可能有其他活要干，我們要盡可能的減少ANR的發(fā)生，所以前面乘以２倍。
假設(shè)現(xiàn)在廣播超時(shí)還沒(méi)處理，滿足if條件，就會(huì)進(jìn)入，打印Hung broadcast ["+ mQueueName + "] discarded after timeout failure....的log，然后執(zhí)行 broadcastTimeoutLocked(false)強(qiáng)制停止廣播，broadcastTimeoutLocked相關(guān)代碼代碼如下：
final void broadcastTimeoutLocked(boolean fromMsg) {
.....
long timeoutTime = r.receiverTime + mTimeoutPeriod;
if (timeoutTime > now) {
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Premature timeout ["
+ mQueueName + "] @ " + now + ": resetting BROADCAST_TIMEOUT_MSG for "
+ timeoutTime);
setBroadcastTimeoutLocked(timeoutTime);
return;
}
}
.....
}
內(nèi)部調(diào)用setBroadcastTimeoutLocked()設(shè)置一個(gè)延遲消息
final void setBroadcastTimeoutLocked(long timeoutTime) {
if (! mPendingBroadcastTimeoutMessage) {
Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);
mHandler.sendMessageAtTime(msg, timeoutTime);
mPendingBroadcastTimeoutMessage = true;
}
}
如果廣播消息能夠處理完畢，就會(huì)執(zhí)行cancelBroadcastTimeoutLocked，將超時(shí)的Message移除掉。
final void cancelBroadcastTimeoutLocked() {
if (mPendingBroadcastTimeoutMessage) {
mHandler.removeMessages(BROADCAST_TIMEOUT_MSG, this);
mPendingBroadcastTimeoutMessage = false;
}
如果廣播消息沒(méi)有在timeout時(shí)間內(nèi)處理掉，下面BroadcastHandler發(fā)送的消息就會(huì)執(zhí)行。
private final class BroadcastHandler extends Handler {
.....
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
.....
case BROADCAST_TIMEOUT_MSG: {
synchronized (mService) {
broadcastTimeoutLocked(true);
}
} break;
.....
}
}
}
再次進(jìn)入broadcastTimeoutLocked方法里面
final void broadcastTimeoutLocked(boolean fromMsg) {
//傳進(jìn)來(lái)是ture
if (fromMsg) {
mPendingBroadcastTimeoutMessage = false;
}
//隊(duì)列沒(méi)有廣播處理了，返回
if (mOrderedBroadcasts.size() == 0) {
return;
}
long now = SystemClock.uptimeMillis();
BroadcastRecord r = mOrderedBroadcasts.get(0);
if (fromMsg) {
//正在執(zhí)行dexopt,返回
if (mService.mDidDexOpt) {
// Delay timeouts until dexopt finishes.
mService.mDidDexOpt = false;
long timeoutTime = SystemClock.uptimeMillis() + mTimeoutPeriod;
setBroadcastTimeoutLocked(timeoutTime);
return;
}
//系統(tǒng)還沒(méi)有進(jìn)入ready狀態(tài)
if (!mService.mProcessesReady) {
// Only process broadcast timeouts if the system is ready. That way
// PRE_BOOT_COMPLETED broadcasts can't timeout as they are intended
// to do heavy lifting for system up.
return;
}
//如果當(dāng)前正在執(zhí)行的receiver沒(méi)有超時(shí)，則重新設(shè)置廣播超時(shí)
long timeoutTime = r.receiverTime + mTimeoutPeriod;
if (timeoutTime > now) {
// We can observe premature timeouts because we do not cancel and reset the
// broadcast timeout message after each receiver finishes. Instead, we set up
// an initial timeout then kick it down the road a little further as needed
// when it expires.
if (DEBUG_BROADCAST) Slog.v(TAG_BROADCAST,
"Premature timeout ["
+ mQueueName + "] @ " + now + ": resetting BROADCAST_TIMEOUT_MSG for "
+ timeoutTime);
setBroadcastTimeoutLocked(timeoutTime);
return;
}
}
//當(dāng)前正在執(zhí)行的receiver沒(méi)有超時(shí)，則重新設(shè)置廣播超時(shí)，處理下一條廣播
BroadcastRecord br = mOrderedBroadcasts.get(0);
if (br.state == BroadcastRecord.WAITING_SERVICES) {
// In this case the broadcast had already finished, but we had decided to wait
// for started services to finish as well before going on. So if we have actually
// waited long enough time timeout the broadcast, let's give up on the whole thing
// and just move on to the next.
Slog.i(TAG, "Waited long enough for: " + (br.curComponent != null
? br.curComponent.flattenToShortString() : "(null)"));
br.curComponent = null;
br.state = BroadcastRecord.IDLE;
processNextBroadcast(false);
return;
}
Slog.w(TAG, "Timeout of broadcast " + r + " - receiver=" + r. receiver
+ ", started " + (now - r.receiverTime) + "ms ago");
r.receiverTime = now;
r.anrCount++;
// Current receiver has passed its expiration date.
if (r.nextReceiver <= 0) {
Slog.w(TAG, "Timeout on receiver with nextReceiver <= 0");
return;
}
ProcessRecord app = null;
String anrMessage = null;
Object curReceiver = r.receivers.get(r.nextReceiver-1);
r.delivery[r.nextReceiver-1] = BroadcastRecord.DELIVERY_TIMEOUT;
Slog.w(TAG, "Receiver during timeout: " + curReceiver);
logBroadcastReceiverDiscardLocked(r);
if (curReceiver instanceof BroadcastFilter) {
BroadcastFilter bf = (BroadcastFilter)curReceiver;
if (bf.receiverList.pid != 0
&& bf.receiverList.pid != ActivityManagerService.MY_PID) {
synchronized (mService.mPidsSelfLocked) {
app = mService.mPidsSelfLocked.get(
bf.receiverList.pid);
}
}
} else {
app = r.curApp;
}
//進(jìn)程存在，anrMessage賦值
if (app != null) {
anrMessage = "Broadcast of " + r.intent.toString();
}
if (mPendingBroadcast == r) {
mPendingBroadcast = null;
}
// Move on to the next receiver.
finishReceiverLocked(r, r.resultCode, r.resultData,
r.resultExtras, r.resultAbort, false);
//處理下一條廣播
scheduleBroadcastsLocked();
if (anrMessage != null) {
// Post the ANR to the handler since we do not want to process ANRs while
// potentially holding our lock.
mHandler.post(new AppNotResponding(app, anrMessage));
}
}
所以當(dāng)一個(gè)receiver超時(shí)后，系統(tǒng)會(huì)放棄繼續(xù)處理它給出ANR提示，并再次調(diào)用scheduleBroadcastsLocked()，嘗試處理下一個(gè)receiver，
private final class AppNotResponding implements Runnable {
private final ProcessRecord mApp;
private final String mAnnotation;
public AppNotResponding(ProcessRecord app, String annotation) {
mApp = app;
mAnnotation = annotation;
}
@Override
public void run() {
//內(nèi)部創(chuàng)建ANR顯示的Dialog
mService.mAppErrors.appNotResponding(mApp, null, null, false, mAnnotation);
}
}
４、廣播攔截處理分析
廣播消息可以有多個(gè)接收者，對(duì)于有序廣播是一個(gè)接著一個(gè)處理的，優(yōu)先級(jí)高的接收者可以優(yōu)先執(zhí)行，并且可以調(diào)用BroadcastReceiver的abortBroadcast()方法攔截廣播，如果我們?cè)趓eceiver的onReceive()中調(diào)用這個(gè)方法，那么它后面的接收者就不會(huì)收到廣播。
public abstract class BroadcastReceiver {
private PendingResult mPendingResult;
public final void abortBroadcast() {
checkSynchronousHint();
mPendingResult.mAbortBroadcast = true;
}
}
```
把BroadcastReceiver::PendingResult的成員變量mAbortBroadcast設(shè)置成true，
final class Args extends BroadcastReceiver.PendingResult implements Runnable {
private Intent mCurIntent;
private final boolean mOrdered;
private boolean mDispatched;
public Args(Intent intent, int resultCode, String resultData, Bundle resultExtras,
boolean ordered, boolean sticky, int sendingUser) {
super(resultCode, resultData, resultExtras,
mRegistered ? TYPE_REGISTERED : TYPE_UNREGISTERED, ordered,
sticky, mIIntentReceiver.asBinder(), sendingUser, intent.getFlags());
mCurIntent = intent;
mOrdered = ordered;
}
public void run() {
.....
try {
ClassLoader cl = mReceiver.getClass().getClassLoader();
intent.setExtrasClassLoader(cl);
intent.prepareToEnterProcess();
setExtrasClassLoader(cl);
//設(shè)置PendingResult，這個(gè)PendingResult中mAbortBroadcast為true
receiver.setPendingResult(this);
receiver.onReceive(mContext, intent);
} catch (Exception e) {
.....
}
if (receiver.getPendingResult() != null) {
//告知AMS處理下一個(gè)廣播
finish();
}
}
}
```
finish()會(huì)告知AMS處理下一個(gè)廣播，在第一小節(jié)已經(jīng)分析過(guò)，最終進(jìn)入AMS的finishReceiver方法
public void finishReceiver(IBinder who, int resultCode, String resultData,
Bundle resultExtras, boolean resultAbort, int flags) {
.....
try {
boolean doNext = false;
BroadcastRecord r;
synchronized(this) {
BroadcastQueue queue = (flags & Intent.FLAG_RECEIVER_FOREGROUND) != 0
? mFgBroadcastQueue : mBgBroadcastQueue;
r = queue.getMatchingOrderedReceiver(who);
if (r != null) {
//resultAbort傳進(jìn)來(lái)是true，
doNext = r.queue.finishReceiverLocked(r, resultCode,
resultData, resultExtras, resultAbort, true);
}
}
//調(diào)用processNextBroadcast處理廣播
if (doNext) {
r.queue.processNextBroadcast(false);
}
trimApplications();
} finally {
Binder.restoreCallingIdentity(origId);
}
}
processNextBroadcast方法中有一個(gè)檢查廣播有沒(méi)有發(fā)送完畢的邏輯。
do {
.....
r = mOrderedBroadcasts.get(0);
//檢查廣播有沒(méi)有發(fā)送完，resultAbort為=ture
if (r.receivers == null || r.nextReceiver >= numReceivers
|| r.resultAbort || forceReceive) {
.....
//mOrderedBroadcasts里刪除廣播消息
mOrderedBroadcasts.remove(0);
r = null;
looped = true;
continue;
}
} while (r == null);
當(dāng)resultAbort為=ture時(shí)候，廣播消息從mOrderedBroadcasts刪除，后面也就收不到廣播了。
５、理解粘性廣播
sticky廣播通過(guò)Context.sendStickyBroadcast()函數(shù)來(lái)發(fā)送，用此函數(shù)發(fā)送的廣播會(huì)一直滯留，當(dāng)有匹配此廣播的廣播接收器被注冊(cè)后，該廣播接收器就會(huì)收到此條信息。使用此函數(shù)需要發(fā)送廣播時(shí)，需要獲得BROADCAST_STICKY權(quán)限。粘性廣播可以使用廣播接收器進(jìn)行接收，但是正確的接收方式是調(diào)用registerReceiver能接受廣播，信息將在調(diào)用registerReceiver的返回值中給出。對(duì)于粘性廣播的發(fā)送，和普通廣播的發(fā)送方式是一致的，例子來(lái)自與Android 粘性廣播StickyBroadcast的使用
private void sendStickyBroadcast(){
Intent i = new Intent();
i.setAction(StickyBroadcastReceiver.Action);
i.putExtra("info", "sticky broadcast has been receiver");
sendStickyBroadcast(i);
Log.i("Other","sticky broadcast send ok!");
}
可以使用BroadcastReceiver來(lái)接收
public class StickyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
//收到廣播
}
}
<!--使用粘性廣播發(fā)送權(quán)限-->
<uses-permission android:name="android.permission.BROADCAST_STICKY" />
IntentFilter intentFilter = new IntentFilter(StickyBroadcastReceiver.Action);
Intent data = registerReceiver(null, intentFilter);
if(data!=null&&StickyBroadcastReceiver.Action.equals(data.getAction())) {
Toast.makeText(this, data.getStringExtra("info"), Toast.LENGTH_SHORT).show();
}
好了廣播的四篇文章寫完了，準(zhǔn)備在分析一波Service吧
