接上篇文章，這篇文章主要是總結前面知識，並且瞭解一些細節問題，加深對廣播機制的理解，比如有播有序是怎麼保證有序的？廣播攔截機制是怎麼實現的?廣播傳送超時了是怎麼處理的?registerReceiver方法發返回值有什麼用?粘性廣播等等。
Android原始碼解析四大元件系列（五）---廣播的註冊過程
Android原始碼解析四大元件系列（六）---廣播的處理過程
Android原始碼解析四大元件系列（七）---廣播的傳送過程
###1、廣播相關資料結構的再次理解
ReceiverDispatcher: 客戶端廣播分發者物件，第一篇講的很清楚了，ReceiverDispatcher的內部類InnerReceiver為binder物件，用於與AMS的傳遞與通訊。
ReceiverList: 繼承自ArrayList，存放了Receiver的binder物件以及其註冊的BroadcastFilter列表。AMS中定義了
final HashMapmRegisteredReceivers = new HashMap<>();key為InnerReceiver的binder物件，值為ReceiverList，ReceiverList內部記錄的是動態註冊的廣播接收者，mRegisteredReceivers只有動態註冊的時候才會有內容。 BroadcastFilter: 封裝了IntentFilter，描述動態廣播，是動態廣播節點。
ResolveInfo:Parcelable子類，描述靜態廣播，是靜態廣播節點。
IntentResolver: 解析Intent，在addFilter時即進行解析。其內部有mSchemeToFilter，mActionToFilter，mTypedActionToFilter三個map物件。key為對應的action（scheme或者type），value為Filter。
BroadcastRecord:描述一個廣播， 將intent等一堆資訊，封裝成BroadcastRecord，交給BroadcastQueue進行處理。
BroadcastQueue: BroadcastQueue為Broadcast處理佇列，分為前臺佇列mFgBroadcastQueue和後臺佇列mBgBroadcastQueue，mFgBroadcastQueue會有更高的許可權，被優先處理。mFgBroadcastQueue和mBgBroadcastQueue兩個佇列中都含有mOrderedBroadcasts和mParallelBroadcasts兩個列表用來表示有序廣播列表和無序廣播列表。
###２、有序廣播是怎麼保證有序的
上一篇文章中說了processNextBroadcast()只會處理一個BroadcastRecord的一個receiver，那怎麼將廣播傳遞給下一個receiver呢？廣播接受者有“動態”和“靜態”之分，廣播訊息也有“序列”和“並行”之分，或者叫“有序”和“無序”之分。廣播的處理方式跟廣播的接收者和廣播訊息型別有關係。有序廣播是怎麼保證有序的這個問題，得分情況討論，對於動態註冊的receiver，先回到最終onReceive回撥的地方，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傳進來的是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方法回撥
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);
}
}
}複製程式碼因為在呼叫onReceive之前，執行了 receiver.setPendingResult(this)，所以在下面receiver.getPendingResult()就不是null,則就進入BroadcastReceiver的內部類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);
}
}複製程式碼finish方法中根據mType的值有兩個分支。mType是PendingResult的成員變數，在PendingResult的建構函式中進行賦值的。
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;
}複製程式碼這個構造方法是在BroadcastReceiver.PendingResult的子類Args中呼叫的
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;
}
}複製程式碼由於mRegistered是動態註冊廣播接收者傳進來的，值是true,所以上面mType的值是TYPE_REGISTERED，由於是有序廣播ordered值是true，那麼mOrderedHint為true,所以要走第二個分支：
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing broadcast to " + mToken);
final IActivityManager mgr = ActivityManagerNative.getDefault();
sendFinished(mgr);複製程式碼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) {
}
}
}複製程式碼有序廣播mOrderedHint值為true,所以進入到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) {
//再次執行processNextBroadcast處理廣播
r.queue.processNextBroadcast(false);
}
trimApplications();
} finally {
Binder.restoreCallingIdentity(origId);
}
}複製程式碼上面是分析了動態的廣播接收者是怎麼按照一個接著一個處理的。在看看靜態註冊的receiver，回到靜態廣播回撥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);
//回撥廣播的onReceive方法
receiver.onReceive(context.getReceiverRestrictedContext(),data.intent);
} catch (Exception e) {
....
}
} finally {
sCurrentBroadcastIntent.set(null);
}
if (receiver.getPendingResult() != null) {
data.finish();
}
}複製程式碼在回撥onReceiver方法之前， 執行了 receiver.setPendingResult(data)，所以下面receiver.getPendingResult() != null成立，走 data.finish()，data是ReceiverData物件，handleReceiver方法傳進來的，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);
}複製程式碼我們看 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);
}
}複製程式碼此時mType分析後值是TYPE_COMPONENT，同樣會走sendFinished，後面AMS的處理邏輯是一樣的，不贅述。
###３、廣播超時是怎麼處理的?
AMS維護了兩個廣播佇列BroadcastQueue，mFgBroadcastQueue，前臺佇列的超時時間是10秒，mBgBroadcastQueue，後臺佇列的超時時間是60秒，如果廣播沒有在規定的時間內處理完就會發生ANR,如果你想你的廣播進入前臺廣播佇列，那麼在傳送的時候，在intent中加入Intent.FLAG_RECEIVER_FOREGROUND標記，如果不加，系統預設是後臺廣播。mFgBroadcastQueue會有更高的許可權，被優先處理。
在processNextBroadcast方法中有下面一段程式碼，與廣播超時有關係，一旦超時就會出現ANR。
do {
int numReceivers = (r.receivers != null) ? r.receivers.size() : 0;
if (mService.mProcessesReady && r.dispatchTime > 0) {
long now = SystemClock.uptimeMillis();
//廣播訊息的第一個ANR監測機制
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); // 超時處理
forceReceive = true;
r.state = BroadcastRecord.IDLE;
}
}
//判斷廣播有沒有處理完畢
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);複製程式碼廣播的超時機制是針對有序廣播來說的，無序廣播一次性全部處理了，肯定不會超時，超時的這段邏輯都在broadcastTimeoutLocked中，首先判斷是否超時，公式：r.dispatchTime + 2×mTimeoutPeriod×numReceivers，現在解釋一下這幾個時間：
dispatchTime的意義是標記實際處理BroadcastRecord的起始時間，有序廣播是一個接著一個進行處理的，第一次dispatchTime=0,並不會進入該條件判斷
mTimeoutPeriod由當前BroadcastQueue的型別決定(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);複製程式碼所以上面公式翻譯過來就是：實際處理BroadcastRecord的起始時間＋廣播預設的超時時間*廣播接收者的數量。話說回來，這個公式為什麼要這麼設計呢？如果一個前臺的廣播訊息有兩個接收者，那麼在２0秒（２ x 10）之內搞定就可以了，也可能第一個訊息執行了15秒，第二個訊息執行４.99秒，即使第一訊息超過了10秒的規定，也不會出現ＡＮＲ。但是系統任務繁忙，可能有其他活要幹，我們要儘可能的減少ANR的發生，所以前面乘以２倍。
假設現在廣播超時還沒處理，滿足if條件，就會進入，列印Hung broadcast ["+ mQueueName + "] discarded after timeout failure....的log，然後執行 broadcastTimeoutLocked(false)強制停止廣播，broadcastTimeoutLocked相關程式碼程式碼如下：
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;
}
}
.....
}複製程式碼內部呼叫setBroadcastTimeoutLocked()設定一個延遲訊息
final void setBroadcastTimeoutLocked(long timeoutTime) {
if (! mPendingBroadcastTimeoutMessage) {
Message msg = mHandler.obtainMessage(BROADCAST_TIMEOUT_MSG, this);
mHandler.sendMessageAtTime(msg, timeoutTime);
mPendingBroadcastTimeoutMessage = true;
}
}複製程式碼如果廣播訊息能夠處理完畢，就會執行cancelBroadcastTimeoutLocked，將超時的Message移除掉。
final void cancelBroadcastTimeoutLocked() {
if (mPendingBroadcastTimeoutMessage) {
mHandler.removeMessages(BROADCAST_TIMEOUT_MSG, this);
mPendingBroadcastTimeoutMessage = false;
}複製程式碼如果廣播訊息沒有在timeout時間內處理掉，下面BroadcastHandler傳送的訊息就會執行。
private final class BroadcastHandler extends Handler {
.....
@Override
public void handleMessage(Message msg) {
switch (msg.what) {
.....
case BROADCAST_TIMEOUT_MSG: {
synchronized (mService) {
broadcastTimeoutLocked(true);
}
} break;
.....
}
}
}複製程式碼再次進入broadcastTimeoutLocked方法裡面
final void broadcastTimeoutLocked(boolean fromMsg) {
//傳進來是ture
if (fromMsg) {
mPendingBroadcastTimeoutMessage = false;
}
//佇列沒有廣播處理了，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;
}
//系統還沒有進入ready狀態
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;
}
//如果當前正在執行的receiver沒有超時，則重新設定廣播超時
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;
}
}
//當前正在執行的receiver沒有超時，則重新設定廣播超時，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;
}
//程式存在，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));
}
}複製程式碼所以當一個receiver超時後，系統會放棄繼續處理它給出ANR提示，並再次呼叫scheduleBroadcastsLocked()，嘗試處理下一個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() {
//內部建立ANR顯示的Dialog
mService.mAppErrors.appNotResponding(mApp, null, null, false, mAnnotation);
}
}複製程式碼###４、廣播攔截處理分析
廣播訊息可以有多個接收者，對於有序廣播是一個接著一個處理的，優先順序高的接收者可以優先執行，並且可以呼叫BroadcastReceiver的abortBroadcast()方法攔截廣播，如果我們在receiver的onReceive()中呼叫這個方法，那麼它後面的接收者就不會收到廣播。
public abstract class BroadcastReceiver {
private PendingResult mPendingResult;
public final void abortBroadcast() {
checkSynchronousHint();
mPendingResult.mAbortBroadcast = true;
}
}複製程式碼把BroadcastReceiver::PendingResult的成員變數mAbortBroadcast設定成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);
//設定PendingResult，這個PendingResult中mAbortBroadcast為true
receiver.setPendingResult(this);
receiver.onReceive(mContext, intent);
} catch (Exception e) {
.....
}
if (receiver.getPendingResult() != null) {
//告知AMS處理下一個廣播
finish();
}
}
}複製程式碼finish()會告知AMS處理下一個廣播，在第一小節已經分析過，最終進入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傳進來是true，
doNext = r.queue.finishReceiverLocked(r, resultCode,
resultData, resultExtras, resultAbort, true);
}
}
//呼叫processNextBroadcast處理廣播
if (doNext) {
r.queue.processNextBroadcast(false);
}
trimApplications();
} finally {
Binder.restoreCallingIdentity(origId);
}
}複製程式碼processNextBroadcast方法中有一個檢查廣播有沒有傳送完畢的邏輯。
do {
.....
r = mOrderedBroadcasts.get(0);
//檢查廣播有沒有傳送完，resultAbort為=ture
if (r.receivers == null || r.nextReceiver >= numReceivers
|| r.resultAbort || forceReceive) {
.....
//mOrderedBroadcasts裡刪除廣播訊息
mOrderedBroadcasts.remove(0);
r = null;
looped = true;
continue;
}
} while (r == null);複製程式碼當resultAbort為=ture時候，廣播訊息從mOrderedBroadcasts刪除，後面也就收不到廣播了。
###５、理解粘性廣播
sticky廣播通過Context.sendStickyBroadcast()函式來傳送，用此函式傳送的廣播會一直滯留，當有匹配此廣播的廣播接收器被註冊後，該廣播接收器就會收到此條資訊。使用此函式需要傳送廣播時，需要獲得BROADCAST_STICKY許可權。粘性廣播可以使用廣播接收器進行接收，但是正確的接收方式是呼叫registerReceiver能接受廣播，資訊將在呼叫registerReceiver的返回值中給出。對於粘性廣播的傳送，和普通廣播的傳送方式是一致的，例子來自與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!");
}複製程式碼可以使用BroadcastReceiver來接收
public class StickyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
//收到廣播
}
}複製程式碼<!--使用粘性廣播傳送許可權-->
<uses-permission android:name="android.permission.BROADCAST_STICKY" />複製程式碼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();
}複製程式碼好了廣播的四篇文章寫完了，準備在分析一波Service吧