LocalBroadcastManager 是V4包中的一个类，主要负责程序内部广播的注册与发送。也就是说，它只是适用代码中注册发送广播，对于在AndroidManifest中注册的广播接收，则不适用。
官方英文解释如下：
Helper to register for and send broadcasts of Intents to local objects within your process. This is has a number of advantages over sending global broadcasts with sendBroadcast(Intent):
接下来如正题，先看一下全局变量：
private final Context mAppContext; private final HashMap<BroadcastReceiver, ArrayList<IntentFilter>> mReceivers = new HashMap(); private final HashMap<String, ArrayList<ReceiverRecord>> mActions = new HashMap(); private final ArrayList<BroadcastRecord> mPendingBroadcasts = new ArrayList(); static final int MSG_EXEC_PENDING_BROADCASTS = 1; private final Handler mHandler; private static final Object mLock = new Object(); private static LocalBroadcastManager mInstance;
mReceivers：记录注册的BroadcastReceiver及其IntentFilter的数组，这里为什么是数组，下面会有讲到。
mActions：记录IntentFilter中的action对应的BroadcastReceiver数组。虽然这里写的是ReceiverRecord类型，但它实际上是一个内部类，主要保存了BroadcastReceiver及其对应的IntentFilter。
mPendingBroadcasts：在发送广播时，会根据Intent的action，找到与之相对应的BroadcastReceiver。还记得吗？action是可以对应多个BroadcastReceiver，所以这里是数组。
mHandler：就做了一件事情，发送广播。
mLock：同步锁。
mInstance：自己本身的实例对象，有经验的可能已经猜到了，没错，LocalBroadcastManager是一个单例。
看一下它的构造方法，标准的单例写法：
public static LocalBroadcastManager getInstance(Context context) {
synchronized (mLock) {
if (mInstance == null) {
mInstance = new LocalBroadcastManager(
context.getApplicationContext());
}
return mInstance;
}
}
private LocalBroadcastManager(Context context) {
this.mAppContext = context;
this.mHandler = new Handler(context.getMainLooper()) {
public void handleMessage(Message msg) {
switch (msg.what) {
case MSG_EXEC_PENDING_BROADCASTS:
LocalBroadcastManager.this.executePendingBroadcasts();
break;
default:
super.handleMessage(msg);
}
}
};
}
而mHandler就是在构造时创建的，内部就做了一件事，发送广播：executePendingBroadcasts。
接下来就看一下如何注册广播接收者：
public void registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
synchronized (this.mReceivers) {
ReceiverRecord entry = new ReceiverRecord(filter, receiver);
ArrayList filters = (ArrayList) this.mReceivers.get(receiver);
if (filters == null) {
filters = new ArrayList(1);
this.mReceivers.put(receiver, filters);
}
filters.add(filter);
for (int i = 0; i < filter.countActions(); i++) {
String action = filter.getAction(i);
ArrayList entries = (ArrayList) this.mActions.get(action);
if (entries == null) {
entries = new ArrayList(1);
this.mActions.put(action, entries);
}
entries.add(entry);
}
}
}
就是将BroadcastReceiver和IntentFilter建立一对多的对应关系。可以通过BroadcastReceiver找到其对应的IntentFilter，也可以通过IntentFilter中的action找到所对应的BroadcastReceiver。这里还要解释一下上面提到的mReceivers中，为什么保存的IntentFilter是数组形式。我们知道，IntentFilter中是可以保存多个action的，这也就是为什么它初始化成1个长度的数组。那么这里的数组的意义，其实很简单，就是能支持传入多个IntentFilter。虽然是支持传入多个IntentFilter，但如果里面的action是同名的话，也还是按同一个处理的，后面代码就能看出，action是以键的方法存起来的。
有注册，就得有取消注册：
public void unregisterReceiver(BroadcastReceiver receiver) {
synchronized (this.mReceivers) {
ArrayList filters = (ArrayList) this.mReceivers.remove(receiver);
if (filters == null) {
return;
}
for (int i = 0; i < filters.size(); i++) {
IntentFilter filter = (IntentFilter) filters.get(i);
for (int j = 0; j < filter.countActions(); j++) {
String action = filter.getAction(j);
ArrayList receivers = (ArrayList) this.mActions.get(action);
if (receivers != null) {
for (int k = 0; k < receivers.size(); k++) {
if (((ReceiverRecord) receivers.get(k)).receiver == receiver) {
receivers.remove(k);
k--;
}
}
if (receivers.size() <= 0)
this.mActions.remove(action);
}
}
}
}
}
最后就是关键的 public boolean sendBroadcast(Intent intent)方法，整个方法都是synchronized (this.mReceivers)的，由于这个方法内容太长，这里分段来讲解：
String action = intent.getAction(); String type = intent.resolveTypeIfNeeded(this.mAppContext.getContentResolver()); Uri data = intent.getData(); String scheme = intent.getScheme(); Set categories = intent.getCategories(); boolean debug = (intent.getFlags() & Intent.FLAG_DEBUG_LOG_RESOLUTION ) != 0;
然后就是从mActions中取出intent的action所对应的ReceiverRecord
ArrayList entries = (ArrayList) this.mActions.get(intent.getAction()); ArrayList receivers = null; for (int i = 0; i < entries.size(); i++)
这段就是for循环里面的内容：
ReceiverRecord receiver = (ReceiverRecord) entries.get(i);
if (receiver.broadcasting) {
} else {
int match = receiver.filter.match(action, type, scheme,
data, categories, "LocalBroadcastManager");
if (match >= 0) {
if (receivers == null) {
receivers = new ArrayList();
}
receivers.add(receiver);
receiver.broadcasting = true;
} else {
}
}
}
最后，添加到ArrayList中：this.mPendingBroadcasts.add(new BroadcastRecord(intent,receivers));通知Handler，执行executePendingBroadcasts()方法。
if (receivers != null) {
for (int i = 0; i < receivers.size(); i++) {
((ReceiverRecord) receivers.get(i)).broadcasting = false;
}
this.mPendingBroadcasts.add(new BroadcastRecord(intent,
receivers));
if (!this.mHandler.hasMessages(MSG_EXEC_PENDING_BROADCASTS)) {
this.mHandler.sendEmptyMessage(MSG_EXEC_PENDING_BROADCASTS);
}
return true;
}executePendingBroadcasts()方法就很简单了，就是取出mPendingBroadcasts数组中的BroadcastReceiver(在ReceiverRecord中保存其对象)，调用其onReceive方法。
private void executePendingBroadcasts() {
while (true) {
BroadcastRecord[] brs = null;
synchronized (this.mReceivers) {
int N = this.mPendingBroadcasts.size();
if (N <= 0) {
return;
}
brs = new BroadcastRecord[N];
this.mPendingBroadcasts.toArray(brs);
this.mPendingBroadcasts.clear();
}
for (int i = 0; i < brs.length; i++) {
BroadcastRecord br = brs[i];
for (int j = 0; j < br.receivers.size(); j++)
((ReceiverRecord) br.receivers.get(j)).receiver.onReceive(
this.mAppContext, br.intent);
}
}
}public void sendBroadcastSync(Intent intent) {
if (sendBroadcast(intent))
executePendingBroadcasts();
}private static class ReceiverRecord {
final IntentFilter filter;
final BroadcastReceiver receiver;
boolean broadcasting;
ReceiverRecord(IntentFilter _filter, BroadcastReceiver _receiver) {
this.filter = _filter;
this.receiver = _receiver;
}
}1、LocalBroadcastManager在创建单例传参时，不用纠结context是取activity的还是Application的，它自己会取到tApplicationContext。
2、LocalBroadcastManager只适用于代码间的，因为它就是保存接口BroadcastReceiver的对象，然后直接调用其onReceive方法。
3、LocalBroadcastManager注册广播后，当该其Activity或者Fragment不需要监听时，记得要取消注册，注意一点：注册与取消注册在activity或者fragment的生命周期中要保持一致，例如onResume，onPause。
4、LocalBroadcastManager虽然支持对同一个BroadcastReceiver可以注册多个IntentFilter，但还是应该将所需要的action都放进一个IntentFilter，即只注册一个IntentFilter，这只是我个人的建议。
5、LocalBroadcastManager所发送的广播action，只能与注册到LocalBroadcastManager中BroadcastReceiver产生互动。如果你遇到了通过LocalBroadcastManager发送的广播，对面的BroadcastReceiver没响应，很可能就是这个原因造成的。
Android编程之LocalBroadcastManager源码详解
原文：http://blog.csdn.net/xyz_fly/article/details/18970569