android 中的LocalBroadcastManager

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。