LocalBroadcastManager

使用

1. 自定义 BroadcastReveicer 子类

public class LocalBroadcastReceiver extends BroadcastReceiver {

    @Override
    public void onReceive(Context arg0, Intent intent) {
        Bitmap bitmap = intent.getParcelableExtra("bitmap");
        image.setImageBitmap(bitmap);
    }
    
} 

2. 注册接收器

localReceiver = new LocalBroadcastReceiver();
LocalBroadcastManager.getInstance(this).registerReceiver(localReceiver, new IntentFilter(ACTION_LOCAL_SEND));

3. 发送广播
   网络请求成功

LocalBroadcastManager.getInstance(TestHttpURLConnection.this)
                            .sendBroadcast(new Intent(ACTION_LOCAL_SEND)
                            .putExtra("bitmap", bitmap));

4. 取消注册

@Override
protected void onDestroy() {
    super.onDestroy();
    LocalBroadcastManager.getInstance(this).unregisterReceiver(localReceiver);
}

实现

public static LocalBroadcastManager getInstance(Context context) {
synchronized (mLock) {
    if (mInstance == null) {
        mInstance = new LocalBroadcastManager(context.getApplicationContext());
    }
    return mInstance;
}
}

private LocalBroadcastManager(Context context) {
mAppContext = context;
mHandler = new Handler(context.getMainLooper()) {

    @Override
    public void handleMessage(Message msg) {
        switch (msg.what) {
            case MSG_EXEC_PENDING_BROADCASTS:
                executePendingBroadcasts();
                break;
            default:
                super.handleMessage(msg);
        }
    }
};
}

单例实现因而私有化构造函数，基于主线程的 Looper 新建了一个 Handler，handleMessage
中会调用接收器对广播的消息进行处理

注册接收器

HashMap> mReceivers
        = new HashMap>();
HashMap> mActions
        = new HashMap>();

public void registerReceiver(BroadcastReceiver receiver, IntentFilter filter) {
synchronized (mReceivers) {
    ReceiverRecord entry = new ReceiverRecord(filter, receiver);
    ArrayList filters = mReceivers.get(receiver);
    if (filters == null) {
        filters = new ArrayList(1);
        mReceivers.put(receiver, filters);
    }
    filters.add(filter);
    for (int i=0; i entries = mActions.get(action);
        if (entries == null) {
            entries = new ArrayList(1);
            mActions.put(action, entries);
        }
        entries.add(entry);
    }
}
} 

mReceivers 存储广播和过滤器信息，以BroadcastReceiver作为 key，IntentFilter链表作为 value。
mReceivers 是接收器和IntentFilter的对应表，主要作用是方便在unregisterReceiver(…)取消注册，同时作为对象锁限制注册接收器、发送广播、取消接收器注册等几个过程的并发访问。

mActions 以Action为 key，注册这个Action的BroadcastReceiver链表为 value。mActions 的主要作用是方便在广播发送后快速得到可以接收它的BroadcastReceiver。

发送广播

先根据Action从mActions中取出ReceiverRecord列表，循环每个ReceiverRecord判断 filter 和 intent 中的action、type、scheme、data、categoried 是否 match，是的话则保存到receivers列表中，发送 what 为MSG_EXEC_PENDING_BROADCASTS的消息，通过 Handler 去处理。

消息处理

private void 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

mPendingBroadcasts转换为数组BroadcastRecord，循环每个receiver，调用其onReceive函数

取消注册

从mReceivers及mActions中移除相应元素。