Android LocalBroadcast 本地广播源码解析

前言：

Android 本地广播实现非常简单，就一个类。android.support.v4.content.LocalBroadcastManager 大概200行代码。我们看下关键的几个地方

注册广播

    public void registerReceiver(@NonNull BroadcastReceiver receiver, @NonNull IntentFilter filter) {synchronized(this.mReceivers) {LocalBroadcastManager.ReceiverRecord entry = new LocalBroadcastManager.ReceiverRecord(filter, receiver);ArrayList<LocalBroadcastManager.ReceiverRecord> filters = (ArrayList)this.mReceivers.get(receiver);if (filters == null) {filters = new ArrayList(1);this.mReceivers.put(receiver, filters);}filters.add(entry);for(int i = 0; i < filter.countActions(); ++i) {String action = filter.getAction(i);ArrayList<LocalBroadcastManager.ReceiverRecord> entries = (ArrayList)this.mActions.get(action);if (entries == null) {entries = new ArrayList(1);this.mActions.put(action, entries);}entries.add(entry);}}}

注册广播主要是把receiver 使用List保存起来。

发送广播

    public boolean sendBroadcast(@NonNull Intent intent) {synchronized(this.mReceivers) {String action = intent.getAction();String type = intent.resolveTypeIfNeeded(this.mAppContext.getContentResolver());Uri data = intent.getData();String scheme = intent.getScheme();Set<String> categories = intent.getCategories();boolean debug = (intent.getFlags() & 8) != 0;if (debug) {Log.v("LocalBroadcastManager", "Resolving type " + type + " scheme " + scheme + " of intent " + intent);}ArrayList<LocalBroadcastManager.ReceiverRecord> entries = (ArrayList)this.mActions.get(intent.getAction());if (entries != null) {if (debug) {Log.v("LocalBroadcastManager", "Action list: " + entries);}ArrayList<LocalBroadcastManager.ReceiverRecord> receivers = null;int i;for(i = 0; i < entries.size(); ++i) {LocalBroadcastManager.ReceiverRecord receiver = (LocalBroadcastManager.ReceiverRecord)entries.get(i);if (debug) {Log.v("LocalBroadcastManager", "Matching against filter " + receiver.filter);}if (receiver.broadcasting) {if (debug) {Log.v("LocalBroadcastManager", "  Filter's target already added");}} else {int match = receiver.filter.match(action, type, scheme, data, categories, "LocalBroadcastManager");if (match >= 0) {if (debug) {Log.v("LocalBroadcastManager", "  Filter matched!  match=0x" + Integer.toHexString(match));}if (receivers == null) {receivers = new ArrayList();}receivers.add(receiver);receiver.broadcasting = true;} }}if (receivers != null) {for(i = 0; i < receivers.size(); ++i) {((LocalBroadcastManager.ReceiverRecord)receivers.get(i)).broadcasting = false;}this.mPendingBroadcasts.add(new LocalBroadcastManager.BroadcastRecord(intent, receivers));if (!this.mHandler.hasMessages(1)) {this.mHandler.sendEmptyMessage(1);}return true;}}return false;}}

发送广播的时候，会根据action 匹配list 里面的所有receiver，找到匹配的receiver 放到mPendingBroadcasts 变量里面，然后通过handler发送消息，在hander 线程里面调用onReceive方法。

mHandler初始化

    private LocalBroadcastManager(Context context) {this.mAppContext = context;this.mHandler = new Handler(context.getMainLooper()) {public void handleMessage(Message msg) {switch(msg.what) {case 1:LocalBroadcastManager.this.executePendingBroadcasts();break;default:super.handleMessage(msg);}}};}

我们看到mHandler其实就是main thread.

回调所有的广播注册者

    void executePendingBroadcasts() {while(true) {LocalBroadcastManager.BroadcastRecord[] brs;synchronized(this.mReceivers) {int N = this.mPendingBroadcasts.size();if (N <= 0) {return;}brs = new LocalBroadcastManager.BroadcastRecord[N];this.mPendingBroadcasts.toArray(brs);this.mPendingBroadcasts.clear();}for(int i = 0; i < brs.length; ++i) {LocalBroadcastManager.BroadcastRecord br = brs[i];int nbr = br.receivers.size();for(int j = 0; j < nbr; ++j) {LocalBroadcastManager.ReceiverRecord rec = (LocalBroadcastManager.ReceiverRecord)br.receivers.get(j);if (!rec.dead) {rec.receiver.onReceive(this.mAppContext, br.intent);}}}}}

因为本地广播实现是使用list 保存所有的receive, 然后在主线程遍历所有的receive，所以本地广播是不能跨进程使用的。

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