1.BroadcastReceiver的理解
BroadcastReceiver本质就是通过Intent来执行应用中的一个方法，在应用中不需要长期存在。BroadcastReceiver可以分两类:1.1 静态接收者 1.2 动态接收者，如果不需要接收广播了，可以通过unregisterReceiver()接口取消注册。BroadcastReceiver的onReceive()方法如果长时间不返回，会引发ANR,因此如果要执行耗时的操作，必须在其他线程中完成，并且不建议在广播中new线程。广播从发送的方式来划分：1.3 普通广播(无序广播) 1.4有序广播(串行广播) 1.5粘性广播:能发给系统中以后注册的接收者，甚至是新安装的应用中的接收者，而前面两种广播只能发给系统已经注册的接收者。粘性广播有两种，一种是普通粘性广播,通过sendStickyBroadcast()方法发送，另一种是有序粘性广播，通过sendStickyOrderedBroadcast()方法发送。
2.广播的注册流程
MainActivity.java中广播注册过程
BroadcastReceiver mBroadcastReceiver = new MyBroadcastReceiver();
IntentFilter intentFilter = new IntentFilter();
intentFilter.addAction(BROADCAST_ACTION);
registerReceiver(mBroadcastReceiver, intentFilter);
class MyBroadcastReceiver extends BroadcastReceiver {
@Override
public void onReceive(Context context, Intent intent) {
}
}#ContextWrapper
@Override
public Intent registerReceiver(
BroadcastReceiver receiver, IntentFilter filter) {
return mBase.registerReceiver(receiver, filter);
} #Context
@Nullable
public abstract Intent registerReceiver(@Nullable BroadcastReceiver receiver,
IntentFilter filter);#ContextImpl
@Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
return registerReceiver(receiver, filter, null, null);
} @Override
public Intent registerReceiver(BroadcastReceiver receiver, IntentFilter filter,
String broadcastPermission, Handler scheduler) {
return registerReceiverInternal(receiver, getUserId(),
filter, broadcastPermission, scheduler, getOuterContext());
}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) {
if (scheduler == null) {
//将主线程Handler赋予scheuler
scheduler = mMainThread.getHandler();
}
//获取IIntentReceiver对象
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 {
//调用AMP.registerReceiver
return ActivityManagerNative.getDefault().registerReceiver(
mMainThread.getApplicationThread(), mBasePackageName,
rd, filter, broadcastPermission, userId);
} catch (RemoteException e) {
return null;
}
}#LoadedApk.java
public IIntentReceiver getReceiverDispatcher(BroadcastReceiver r, Context context, Handler handler, Instrumentation instrumentation, boolean registered) {
synchronized (mReceivers) {
LoadedApk.ReceiverDispatcher rd = null;
ArrayMap<BroadcastReceiver, LoadedApk.ReceiverDispatcher> map = null;
//此处registered=true，则进入该分支
if (registered) {
map = mReceivers.get(context);
if (map != null) {
rd = map.get(r);
}
}
if (rd == null) {
//当广播分发者为空，则创建ReceiverDispatcher
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 {
//验证广播分发者的context、handler是否一致
rd.validate(context, handler);
}
rd.mForgotten = false;
//获取IIntentReceiver对象
return rd.getIIntentReceiver();
}
}ActivityManagerNative.getDefault()返回的是ActivityManagerProxy对象，简称AMP. 该方法中参数有mMainThread.getApplicationThread()返回的是ApplicationThread。
# ActivityManagerNative
public Intent registerReceiver(IApplicationThread caller, String packageName,
IIntentReceiver receiver,
IntentFilter filter, String perm, int userId) throws RemoteException
{
Parcel data = Parcel.obtain();
Parcel reply = Parcel.obtain();
data.writeInterfaceToken(IActivityManager.descriptor);
data.writeStrongBinder(caller != null ? caller.asBinder() : null);
data.writeString(packageName);
data.writeStrongBinder(receiver != null ? receiver.asBinder() : null);
filter.writeToParcel(data, 0);
data.writeString(perm);
data.writeInt(userId);
//向服务端AMS发起注册广播的动作
mRemote.transact(REGISTER_RECEIVER_TRANSACTION, data, reply, 0);
reply.readException();
Intent intent = null;
int haveIntent = reply.readInt();
if (haveIntent != 0) {
intent = Intent.CREATOR.createFromParcel(reply);
}
reply.recycle();
data.recycle();
return intent;
}#ActivityManagerService
public Intent registerReceiver(IApplicationThread caller, String callerPackage,
IIntentReceiver receiver, IntentFilter filter, String permission, int userId,
int flags) {
...
int callingUid;
int callingPid;
boolean instantApp;
synchronized(this) {
if (caller != null) {
//查询调用者的进程信息
callerApp = getRecordForAppLocked(caller);
...
instantApp = isInstantApp(callerApp, callerPackage, callingUid);
userId = mUserController.handleIncomingUser(callingPid, callingUid, userId, true,
ALLOW_FULL_ONLY, "registerReceiver", callerPackage);
//获取IntentFilter中的actions,就是在intentFilter.addAction(BROADCAST_ACTION);中需要
//监听的广播action
Iterator<String> actions = filter.actionsIterator();
if (actions == null) {
ArrayList<String> noAction = new ArrayList<String>(1);
noAction.add(null);
actions = noAction.iterator();
}
...
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);
//查询匹配的sticky广播
if (filter.match(resolver, intent, true, TAG) >= 0) {
if (allSticky == null) {
allSticky = new ArrayList<Intent>();
}
//匹配成功，则将给intent添加到allSticky队列
allSticky.add(intent);
}
}
}
//当IIntentReceiver为空，则直接返回第一个sticky Intent，
Intent sticky = allSticky != null ? allSticky.get(0) : null;
if (receiver == null) {
return sticky;
}
synchronized (this) {
//创建BroadcastFilter对象，并添加到接收者队列
BroadcastFilter bf = new BroadcastFilter(filter, rl, callerPackage,
permission, callingUid, userId, instantApp, visibleToInstantApps);
rl.add(bf);
if (!bf.debugCheck()) {
Slog.w(TAG, "==> For Dynamic broadcast");
}
//新创建的广播过滤者，添加到ReceiverResolver队列
mReceiverResolver.addFilter(bf);
// Enqueue broadcasts for all existing stickies that match
// this filter.
//所有匹配该filter的sticky广播执行入队操作
//如果没有使用sendStickyBroadcast，则allSticky=null。
if (allSticky != null) {
ArrayList receivers = new ArrayList();
receivers.add(bf);
final int stickyCount = allSticky.size();
for (int i = 0; i < stickyCount; i++) {
Intent intent = allSticky.get(i);
//根据intent返回前台或后台广播队列
BroadcastQueue queue = broadcastQueueForIntent(intent);
//创建BroadcastRecord
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);
//该广播加入到并行广播队列
queue.enqueueParallelBroadcastLocked(r);
//调度广播，发送BROADCAST_INTENT_MSG消息，触发处理下一个广播。
queue.scheduleBroadcastsLocked();
}
}
return sticky;
}
}# IntentFilter
public final int match(ContentResolver resolver, Intent intent,
boolean resolve, String logTag) {
String type = resolve ? intent.resolveType(resolver) : intent.getType();
return match(intent.getAction(), type, intent.getScheme(),
intent.getData(), intent.getCategories(), logTag);
}public final int match(String action, String type, String scheme,
Uri data, Set<String> categories, String logTag) {
//不存在匹配的action
if (action != null && !matchAction(action)) {
if (false) Log.v(
logTag, "No matching action " + action + " for " + this);
return NO_MATCH_ACTION;
}
//不存在匹配的type或data
int dataMatch = matchData(type, scheme, data);
if (dataMatch < 0) {
...
return dataMatch;
}
//不存在匹配的category
String categoryMismatch = matchCategories(categories);
if (categoryMismatch != null) {
if (false) {
Log.v(logTag, "No matching category " + categoryMismatch + " for " + this);
}
return NO_MATCH_CATEGORY;
}
// It would be nice to treat container activities as more
// important than ones that can be embedded, but this is not the way...
if (false) {
if (categories != null) {
dataMatch -= mCategories.size() - categories.size();
}
}
return dataMatch;
}2 广播的发送过程
#ContextImpl.java
public void sendBroadcast(Intent intent) {
warnIfCallingFromSystemProcess();
String resolvedType = intent.resolveTypeIfNeeded(getContentResolver());
try {
intent.prepareToLeaveProcess();
// 调用AMP.broadcastIntent
ActivityManagerNative.getDefault().broadcastIntent(
mMainThread.getApplicationThread(), intent, resolvedType, null,
Activity.RESULT_OK, null, null, null, AppOpsManager.OP_NONE, null, false, false,
getUserId());
} catch (RemoteException e) {
...
}
}#ActivityManagerNative.java
public int broadcastIntent(IApplicationThread caller, Intent intent, String resolvedType, IIntentReceiver resultTo, int resultCode, String resultData, Bundle map, String[] requiredPermissions, int appOp, Bundle options, boolean serialized, boolean sticky, int userId) 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.writeStringArray(requiredPermissions);
data.writeInt(appOp);
data.writeBundle(options);
data.writeInt(serialized ? 1 : 0);
data.writeInt(sticky ? 1 : 0);
data.writeInt(userId);
mRemote.transact(BROADCAST_INTENT_TRANSACTION, data, reply, 0);
reply.readException();
int res = reply.readInt();
reply.recycle();
data.recycle();
return res;
} #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 options, boolean serialized, boolean sticky, int userId) {
enforceNotIsolatedCaller("broadcastIntent");
synchronized(this) {
//验证广播intent是否有效
intent = verifyBroadcastLocked(intent);
//获取调用者进程记录对象
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, resultExtras,
requiredPermissions, appOp, null, serialized, sticky,
callingPid, callingUid, userId);
Binder.restoreCallingIdentity(origId);
return res;
}
}# ActivityManagerService
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 {
......
//首先是根据intent找出相应的广播接收器
registeredReceivers = mReceiverResolver.queryIntent(intent, resolvedType, false);
}
} catch (RemoteException ex) {
......
}
//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
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;
}
}
}
//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
if (!replaced) {
mParallelBroadcasts.add(r);
scheduleBroadcastsLocked();
}
registeredReceivers = null;
NR = 0;
}
}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.
#ActivityManagerService
final Handler mHandler = new Handler() {
public void handleMessage(Message msg) {
switch (msg.what) {
......
case BROADCAST_INTENT_MSG: {
......
processNextBroadcast(true);
} break;
......
}
}
}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。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deliverToRegisteredReceiverLocked函数执行.
#ActivityManagerService
private final void deliverToRegisteredReceiverLocked(BroadcastRecord r,
BroadcastFilter filter, boolean ordered) {
boolean skip = false;
...
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) {
......
......
}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：没标明类的方法说明最近的类相同。
#ActivityThread #ApplicationThreadProxy
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);
}#LoadedApk #InnerReceiver
final class LoadedApk {
......
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;
}
@Override
public void performReceive(Intent intent, int resultCode, String data,
Bundle extras, boolean ordered, boolean sticky, int sendingUser) {
final LoadedApk.ReceiverDispatcher rd;
if (intent == null) {
Log.wtf(TAG, "Null intent received");
rd = null;
} else {
rd = mDispatcher.get();
}
...
if (rd != null) {
rd.performReceive(intent, resultCode, data, extras,
ordered, sticky, sendingUser);
} else {
...
IActivityManager mgr = ActivityManagerNative.getDefault();
try {
if (extras != null) {
extras.setAllowFds(false);
}
mgr.finishReceiver(this, resultCode, data, extras, false, intent.getFlags());
} catch (RemoteException e) {
throw e.rethrowFromSystemServer();
}
}
}
}#InnerReceiver
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);
if (intent == null) {
Log.wtf(TAG, "Null intent received");
} else {
if (ActivityThread.DEBUG_BROADCAST) {
int seq = intent.getIntExtra("seq", -1);
Slog.i(ActivityThread.TAG, "Enqueueing broadcast " + intent.getAction()
+ " seq=" + seq + " to " + mReceiver);
}
}
if (intent == null || !mActivityThread.post(args)) {
if (mRegistered && ordered) {
IActivityManager mgr = ActivityManagerNative.getDefault();
if (ActivityThread.DEBUG_BROADCAST) Slog.i(ActivityThread.TAG,
"Finishing sync broadcast to " + mReceiver);
args.sendFinished(mgr);
}
}
}
} 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receiver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。
