对于LocalBroadcastManager在google官方文档中也说得很清楚，比较简短，也很好看懂，可以去看看。
Helper to register for and send broadcasts of Intents to local objects within your process. This has a number of advantages over sending global broadcasts with sendBroadcast(Intent):
- You know that the data you are broadcasting won't leave your app, so don't need to worry about leaking private data.
- It is not possible for other applications to send these broadcasts to your app, so you don't need to worry about having security holes they can exploit.
- It is more efficient than sending a global broadcast through the system.
大体介绍就是这些，顾名思义，本地广播(注册)，数据安全，其他app也不能给你发广播(接收)。也比系统广播高效。
使用十分简单：
注册(接收)：
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
if(savedInstanceState!=null) {
if(mLocalBroadcastManager!=null && mBoradCast!=null) {
mLocalBroadcastManager.unregisterReceiver(mBoradCast);
mLocalBroadcastManager=null;
mBoradCast=null;
}
}
mLocalBroadcastManager=LocalBroadcastManager.getInstance(this);
mBoradCast = new MyBroadCast(); IntentFilter intentFilter = new IntentFilter();
//重点在这里，本地注册，本地接收。
mLocalBroadcastManager.registerReceiver(mBoradCast, intentFilter);
}
@Override
protected void onDestroy() {
super.onDestroy();
if(mLocalBroadcastManager!=null && mBoradCast!=null) {
mLocalBroadcastManager.unregisterReceiver(mBoradCast);
mLocalBroadcastManager=null;
mBoradCast=null;
}
}
发送：
LocalBroadcastManager lcm=LocalBroadcastManager.getInstance(mContext);
lcm.sendBroadcast(new Intent(ACTION_LOCATION));//发送
以上则是简单的使用。那么来说说为何呢：有兴趣去看看LocalBroadcastManager。
注册这里可以看到，它其实是一个单例，针对本应用进程的。：
public static LocalBroadcastManager More ...getInstance(Context context) {
synchronized (mLock) {
if (mInstance == null) {
mInstance = new LocalBroadcastManager(context.getApplicationContext());//应用的上下文
}
return mInstance;
}
}
private More ...LocalBroadcastManager(Context context) {
mAppContext = context;
//用主线程注册
handler mHandler = new Handler(context.getMainLooper()) {
@Override public void More ...handleMessage(Message msg) {
switch (msg.what) {
case MSG_EXEC_PENDING_BROADCASTS:
executePendingBroadcasts();
break;
default:
super.handleMessage(msg);
}
}
};
}```
注册的代码：
private final HashMap<BroadcastReceiver, ArrayList<IntentFilter>> mReceivers = new HashMap<BroadcastReceiver, ArrayList<IntentFilter>>();
public void More ...registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
synchronized (mReceivers) {
ReceiverRecord entry = new ReceiverRecord(filter, receiver);
ArrayList<IntentFilter> filters = mReceivers.get(receiver);
if (filters == null) {
filters = new ArrayList<IntentFilter>(1);
//这里很明显是用的一个HashMap来装的我们注册的receiver和filter mReceivers.put(receiver, filters);
}
filters.add(filter);
for (int i=0; i<filter.countActions(); i++) {
String action = filter.getAction(i);
ArrayList<ReceiverRecord> entries = mActions.get(action);
if (entries == null) {
entries = new ArrayList<ReceiverRecord>(1);
mActions.put(action, entries);
}
entries.add(entry);
}
}
}
取消注册:
public void More ...unregisterReceiver(BroadcastReceiver receiver) {
synchronized (mReceivers) {
ArrayList<IntentFilter> filters = mReceivers.remove(receiver);
if (filters == null) {
return;8
}
for (int i=0; i<filters.size(); i++) {
IntentFilter filter = filters.get(i);
for (int j=0; j<filter.countActions(); j++) {
String action = filter.getAction(j);
ArrayList<ReceiverRecord> receivers = mActions.get(action);
if (receivers != null) {
for (int k=0; k<receivers.size(); k++) {
if (receivers.get(k).receiver == receiver) {
//从Map里移除
receivers.remove(k);
k--;
}
}
if (receivers.size() <= 0) {
mActions.remove(action);
}
}
}
}
}
}```
发送广播，截取一部分：
if (receivers != null) {
for (int i=0; i<receivers.size(); i++) {
receivers.get(i).broadcasting = false;
}
mPendingBroadcasts.add(new BroadcastRecord(intent, receivers));
if (!mHandler.hasMessages(MSG_EXEC_PENDING_BROADCASTS)) {
mHandler.sendEmptyMessage(MSG_EXEC_PENDING_BROADCASTS);
}
return true;
}
private void More ...executePendingBroadcasts() {
while (true) {
BroadcastRecord[] brs = null;
synchronized (mReceivers) {
final int N = mPendingBroadcasts.size();
if (N <= 0) {
return;
}
brs = new BroadcastRecord[N];
mPendingBroadcasts.toArray(brs);
mPendingBroadcasts.clear();
}
for (int i=0; i<brs.length; i++) {
BroadcastRecord br = brs[i];
for (int j=0; j<br.receivers.size(); j++) {
//重点在这里，每个注册的都调用了我们注册的onReceive方法(让其自行接收处理)。
br.receivers.get(j).receiver.onReceive(mAppContext, br.intent);
}
}
}
}
这就大致了解了工作原理了。使用起来是很方便的，单例效率也高。所以如果不是非本地注册本地接收的，还是使用LocalBroadcastManager更好。如果是更新图库等，需要系统接收的除外。
