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這篇文章主要為大家展示了“Android Broadcast原理分析之registerReceiver有什么用”，內(nèi)容簡(jiǎn)而易懂，條理清晰，希望能夠幫助大家解決疑惑，下面讓小編帶領(lǐng)大家一起研究并學(xué)習(xí)一下“Android Broadcast原理分析之registerReceiver有什么用”這篇文章吧。
廣播作為四大組件之一，在平時(shí)開(kāi)發(fā)過(guò)程中會(huì)大量使用到，使用方式也是多種多樣的，既可以自己在manifest中注冊(cè)，也可以在java代碼中動(dòng)態(tài)注冊(cè)，既可以接收由系統(tǒng)發(fā)出的廣播，也可以接受自己定義并發(fā)送的廣播。廣播可以實(shí)現(xiàn)進(jìn)程內(nèi)以及跨進(jìn)程之間的通信。從本文開(kāi)始將分別介紹廣播的注冊(cè)，廣播的派發(fā)，本地廣播（LocalBroadcast）以及Android O上對(duì)廣播的限制，本文主要介紹廣播動(dòng)態(tài)注冊(cè)。
從注冊(cè)方式上區(qū)分：動(dòng)態(tài)注冊(cè)以及靜態(tài)注冊(cè)（顯示廣播和隱式廣播）
從發(fā)送方式上區(qū)分：無(wú)序廣播和有序廣播
從處理類型上區(qū)分：前臺(tái)廣播和后臺(tái)廣播
從運(yùn)行方式上區(qū)分：普通廣播和Sticky廣播（已棄用）
從發(fā)送者區(qū)分：系統(tǒng)廣播和自定義廣播
此外還有protect broadcast（只允許指定應(yīng)用可以發(fā)送）
sticky廣播：系統(tǒng)保存了一部分廣播的狀態(tài)，當(dāng)你注冊(cè)的時(shí)候，不需要等到下次這個(gè)廣播發(fā)出來(lái)，直接把最近上一次發(fā)送的這個(gè)廣播返回給你
以上的這些概念在接下來(lái)的介紹中都會(huì)逐個(gè)涉及。
其中的APP，ContextImpl，LoadedApk，ActivityManagerProxy都在APP本身的進(jìn)程中，ActivityManagerService在system_server進(jìn)程中。
首先在APP的進(jìn)程中發(fā)起廣播的注冊(cè)，通過(guò)registerReceiver接口，這個(gè)方法有很多重載方法，但是最終的入口都是在ContextImpl中，后面會(huì)詳細(xì)介紹
從之前的Context的學(xué)習(xí)可以知道，registerReceiver最終調(diào)用的實(shí)現(xiàn)在ContextImpl
如果沒(méi)有指定處理廣播的handler，則默認(rèn)使用主線程的handler
獲取要注冊(cè)的ReceiverDispatcher，在注冊(cè)的Context相同的情況下，每個(gè)Receiver對(duì)應(yīng)一個(gè)ReceiverDispatcher
通過(guò)binder call到systemserver進(jìn)行廣播注冊(cè)
private Intent registerReceiverInternal(BroadcastReceiver receiver, int userId,
IntentFilter filter, String broadcastPermission,
Handler scheduler, Context context, int flags) {
IIntentReceiver rd = null;
if (receiver != null) {
if (mPackageInfo != null && context != null) {
if (scheduler == null) {
// 注冊(cè)receiver的時(shí)候可以指定接受recover的Handler
// 如果沒(méi)有指定，則默認(rèn)用主線程的handler處理
scheduler = mMainThread.getHandler();
}
// 獲取IIntentReceiver
// 這個(gè)是一個(gè)Binder對(duì)象，當(dāng)廣播來(lái)臨時(shí)，用于AMS向客戶端發(fā)起回調(diào)
rd = mPackageInfo.getReceiverDispatcher(
receiver, context, scheduler,
mMainThread.getInstrumentation(), true);
} else {
if (scheduler == null) {
scheduler = mMainThread.getHandler();
}
rd = new LoadedApk.ReceiverDispatcher(
receiver, context, scheduler, null, true).getIIntentReceiver();
}
}
try {
// binder call至AMS，進(jìn)行廣播注冊(cè)
final Intent intent = ActivityManager.getService().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName, rd, filter,
broadcastPermission, userId, flags);
if (intent != null) {
intent.setExtrasClassLoader(getClassLoader());
intent.prepareToEnterProcess();
}
return intent;
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}參數(shù)解析：
receiver：將要注冊(cè)的receiver
userId：用戶空間標(biāo)志，默認(rèn)情況下我們都只有一個(gè)user，現(xiàn)在一些手機(jī)推出的分身，其實(shí)就是用的第二個(gè)user，這種情況下userid會(huì)變，否則默認(rèn)主空間的都是0
IntentFilter：要注冊(cè)的廣播的filter
broadcastPermission：指定要注冊(cè)的廣播的權(quán)限
scheduler：指定廣播接受（也就是onReceive）所在的線程，也就是說(shuō)注冊(cè)的時(shí)候就可以指定好廣播處理放在哪個(gè)線程，如果receiver中事情太多，可以放在另外一個(gè)線程，這樣可以避免主線程被卡住
context：通過(guò)getOuterContext獲取到，前面在介紹context的時(shí)候有提到，application/service/activity中獲取到的是不一樣的
flags:注冊(cè)廣播所攜帶的flag
public IIntentReceiver getReceiverDispatcher(BroadcastReceiver r,
Context context, Handler handler,
Instrumentation instrumentation, boolean registered) {
synchronized (mReceivers) {
// 如果Context相同，每個(gè)receiver對(duì)應(yīng)一個(gè)ReceiverDispatcher
LoadedApk.ReceiverDispatcher rd = null;
ArrayMap<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 ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher>();
mReceivers.put(context, map);
}
map.put(r, rd);
}
} else {
rd.validate(context, handler);
}
rd.mForgotten = false;
return rd.getIIntentReceiver();
}
}mReceivers是一個(gè)二級(jí)map，一級(jí)key是context，二級(jí)key是BroadcastReceiver，value是ReceiverDispatcher。
這里的ReceiverDispatcher又是什么呢？
它是LoadedApk中的一個(gè)內(nèi)部類，保存了這個(gè)receiver的信息，用于在廣播派發(fā)到本進(jìn)程的時(shí)候執(zhí)行，上面這方法最重要的是getIIntentReceiver，這個(gè)就非常重要了，它是一個(gè)Binder對(duì)象，說(shuō)在廣播注冊(cè)的時(shí)候?qū)⑦@個(gè)binder對(duì)象傳遞到了AMS，然后當(dāng)廣播派發(fā)到本進(jìn)程的時(shí)候，通過(guò)這個(gè)binder對(duì)象再會(huì)調(diào)回來(lái)，它在ReceiverDispatcher創(chuàng)建的時(shí)候創(chuàng)建。
static final class ReceiverDispatcher {
// 是一個(gè)binder對(duì)象
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;
}
@Override
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
// 這里就是廣播真正派發(fā)到本進(jìn)程的時(shí)候從systemserver binder call過(guò)來(lái)執(zhí)行的
...
}
final IIntentReceiver.Stub mIIntentReceiver;
final BroadcastReceiver mReceiver;
final Context mContext;
final Handler mActivityThread;
final Instrumentation mInstrumentation;
final boolean mRegistered;
final IntentReceiverLeaked mLocation;
RuntimeException mUnregisterLocation;
boolean mForgotten;
...
}到這里，廣播注冊(cè)在APP進(jìn)程的流程就走完了，主要做了幾件事：
獲取handler
獲取ReceiverDispatcher
獲取InnerReceiver
將上面這些連帶receiver的相關(guān)信息，發(fā)起binder call到ActivityManagerService
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId,
int flags) {
enforceNotIsolatedCaller("registerReceiver");
ArrayList<Intent> stickyIntents = null;
ProcessRecord callerApp = null;
final boolean visibleToInstantApps
= (flags & Context.RECEIVER_VISIBLE_TO_INSTANT_APPS) != 0;
int callingUid;
int callingPid;
boolean instantApp;
synchronized(this) {
if (caller != null) {
// 正常來(lái)講caller是發(fā)起binder call的客戶端進(jìn)程對(duì)應(yīng)的ApplicationThread對(duì)象
// 如果為null則拋異常
callerApp = getRecordForAppLocked(caller);
if (callerApp == null) {
throw new SecurityException(
"Unable to find app for caller " + caller
+ " (pid=" + Binder.getCallingPid()
+ ") when registering receiver " + receiver);
}
if (callerApp.info.uid != SYSTEM_UID &&
!callerApp.pkgList.containsKey(callerPackage) &&
!"android".equals(callerPackage)) {
throw new SecurityException("Given caller package " + callerPackage
+ " is not running in process " + callerApp);
}
callingUid = callerApp.info.uid;
callingPid = callerApp.pid;
} else {
callerPackage = null;
callingUid = Binder.getCallingUid();
callingPid = Binder.getCallingPid();
}
// 判斷caller是否為instant app
instantApp = isInstantApp(callerApp, callerPackage, callingUid);
userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
ALLOW_FULL_ONLY, "registerReceiver", callerPackage);
// 獲取廣播注冊(cè)的filter中的action封裝到list中
Iterator<String> actions = filter.actionsIterator();
if (actions == null) {
ArrayList<String> noAction = new ArrayList<String>(1);
noAction.add(null);
actions = noAction.iterator();
}
// mStickyBroadcasts是一個(gè)二級(jí)map
// 一級(jí)key是userId，二級(jí)key是廣播對(duì)應(yīng)的action，value是廣播對(duì)應(yīng)intent的list（一般只有一個(gè)intent）
// 這里是為了查詢對(duì)于當(dāng)前user，本次注冊(cè)的所有action對(duì)應(yīng)的sticky廣播的intent
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);
}
}
}
}
}
ArrayList<Intent> allSticky = null;
// 這里不為null表示本次注冊(cè)的廣播中有sticky廣播
if (stickyIntents != null) {
final ContentResolver resolver = mContext.getContentResolver();
// 查找匹配的sticky廣播
for (int i = 0, N = stickyIntents.size(); i < N; i++) {
Intent intent = stickyIntents.get(i);
// 如果caller是instant app，且intent的flag不允許對(duì)instant可見(jiàn)，則跳過(guò)
if (instantApp &&
(intent.getFlags() & Intent.FLAG_RECEIVER_VISIBLE_TO_INSTANT_APPS) == 0) {
continue;
}
// If intent has scheme "content", it will need to acccess
// provider that needs to lock mProviderMap in ActivityThread
// and also it may need to wait application response, so we
// cannot lock ActivityManagerService here.
if (filter.match(resolver, intent, true, TAG) >= 0) {
if (allSticky == null) {
allSticky = new ArrayList<Intent>();
}
allSticky.add(intent);
}
}
}
// 直接把最近的一個(gè)匹配到的sticky廣播返回
Intent sticky = allSticky != null ? allSticky.get(0) : null;
// 廣播注冊(cè)的時(shí)候receiver是可以為null的，這種情況下這里直接return
if (receiver == null) {
return sticky;
}
synchronized (this) {
// 校驗(yàn)caller進(jìn)程是否正常
if (callerApp != null && (callerApp.thread == null
|| callerApp.thread.asBinder() != caller.asBinder())) {
// Original caller already died
return null;
}
// mRegisteredReceivers中存放了所有的已注冊(cè)的receiver
// 每個(gè)BroadcastReceiver對(duì)應(yīng)一個(gè)InnerReceiver，即Binder對(duì)象
// binder對(duì)象做key，value是ReceiverList
// ReceiverList是一個(gè)ArrayList
ReceiverList rl = mRegisteredReceivers.get(receiver.asBinder());
if (rl == null) {
rl = new ReceiverList(this, callerApp, callingPid, callingUid,
userId, receiver);
if (rl.app != null) {
rl.app.receivers.add(rl);
} else {
try {
// 如果是新創(chuàng)建的receiver，還需要linkToDeath
receiver.asBinder().linkToDeath(rl, 0);
} catch (RemoteException e) {
return sticky;
}
rl.linkedToDeath = true;
}
// 放入mRegisteredReceivers
mRegisteredReceivers.put(receiver.asBinder(), rl);
} else if (rl.uid != callingUid) {
throw new IllegalArgumentException(
"Receiver requested to register for uid " + callingUid
+ " was previously registered for uid " + rl.uid
+ " callerPackage is " + callerPackage);
} else if (rl.pid != callingPid) {
throw new IllegalArgumentException(
"Receiver requested to register for pid " + callingPid
+ " was previously registered for pid " + rl.pid
+ " callerPackage is " + callerPackage);
} else if (rl.userId != userId) {
throw new IllegalArgumentException(
"Receiver requested to register for user " + userId
+ " was previously registered for user " + rl.userId
+ " callerPackage is " + callerPackage);
}
// 每一個(gè)IntentFilter對(duì)應(yīng)一個(gè)BroadcastFilter
BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
permission, callingUid, userId, instantApp, visibleToInstantApps);
// receiverList中存放了通過(guò)這個(gè)receiver注冊(cè)的所有的filter
// 每調(diào)用一次register就會(huì)add一次
rl.add(bf);
// mReceiverResolver中存放所有的BroadcastFilter
mReceiverResolver.addFilter(bf);
// 有匹配的sticky廣播，則直接開(kāi)始調(diào)度派發(fā)
if (allSticky != null) {
ArrayList receivers = new ArrayList();
receivers.add(bf);
// 對(duì)于每一個(gè)sticky廣播，創(chuàng)建BroadcastRecord并入隊(duì)（并行）
final int stickyCount = allSticky.size();
for (int i = 0; i < stickyCount; i++) {
Intent intent = allSticky.get(i);
// 根據(jù)flag是否有FLAG_RECEIVER_FOREGROUND判斷入隊(duì)是前臺(tái)還是后臺(tái)隊(duì)列
BroadcastQueue queue = broadcastQueueForIntent(intent);
BroadcastRecord r = new BroadcastRecord(queue, intent, null,
null, -1, -1, false, null, null, AppOpsManager.OP_NONE, null, receivers,
null, 0, null, null, false, true, true, -1);
// 入隊(duì)，并行隊(duì)列
queue.enqueueParallelBroadcastLocked(r);
// 啟動(dòng)廣播的調(diào)度，也就是開(kāi)始派發(fā)廣播
queue.scheduleBroadcastsLocked();
}
}
return sticky;
}
}上面主要做了幾件事情：
對(duì)caller的判斷
遍歷action，查詢是否有匹配的sticky廣播
將本次注冊(cè)的廣播放到mRegisteredReceivers中記錄
如果是sticky廣播，開(kāi)始派發(fā)
以上是“Android Broadcast原理分析之registerReceiver有什么用”這篇文章的所有內(nèi)容，感謝各位的閱讀！相信大家都有了一定的了解，希望分享的內(nèi)容對(duì)大家有所幫助，如果還想學(xué)習(xí)更多知識(shí)，歡迎關(guān)注億速云行業(yè)資訊頻道！
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