Android本地广播LocalBroadcastManager源码解析

序言

Broadcast作为Android的四大组件之一，重要性不言而喻；一般我们使用广播的方式通常如下，继承BroadcastReceiver，新建一个广播类。

public class MyBroadcastReceiver extends BroadcastReceiver {
public static final String TAG = "MyBroadcastReceiver";
@Override
public void onReceive(Context context, Intent intent) {
}
}


然后在Activity中注册

IntentFilter filter = new IntentFilter();
filter.addAction("ceshi");
registerReceiver(new MyBroadcastReceiver(), filter);


在需要的时候发送

Intent intent = new Intent();
intent.setAction("ceshi");
sendBroadcast(intent);


这个时候就会回调MyBroadcastReceiver的onReceive方法，然后在方法中处理你的逻辑, 但是这种方式的广播是系统级别的，就是说如果我在A，B App中都注册了action=&＃8221;ceshi&＃8221;的广播，然后A App发送的action=&＃8221;ceshi&＃8221;的广播不止会回调A App中的onReceive方法，也会回调B App中的onReceive方法, 就好比：我们所有的App都注册了系统的Wifi状态切换广播，那Wifi状态有变化的时候，所有App都会收到这条广播。

但是有时候我们的业务需求只需要在自己App中发送接受广播就可以了，没必要用系统级别广播，那还有其它方法可以实现这种需求吗？当然有了，就是我们今天要讲的LocalBroadcastManager，从字面意思就可以看出它是针对本地广播的，那现在让我们通过源码来看看它内部的实现逻辑。

使用

注册方法：

BroadcastReceiver br = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
}
};
LocalBroadcastManager.getInstance(this).registerReceiver(br,new IntentFilter());


发送广播方法：

LocalBroadcastManager.getInstance(this).sendBroadcast(new Intent());


解绑方法：

LocalBroadcastManager.getInstance(this).unregisterReceiver(br);


得到实例方法：

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


从上面方法可以看出LocalBroadcastManager是一个单例全局对象，并且它的几个核心方法和系统级别广播的方法调用是一致的，那下面让我们来通过源码来分析一下它几个核心方法的实现。

源码

注册方法源码

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 String action = filter.getAction(i);
ArrayList entries = mActions.get(action);
if (entries == null) {
entries = new ArrayList(1);
mActions.put(action, entries);
}
entries.add(entry);
}
}
}


首先它new了一个ReceiverRecord对象，ReceiverRecord对象里面有两个3个属性

IntentFilter filter；
BroadcastReceiver receiver；
boolean broadcasting；


然后通过mReceivers.get(receiver)得到一个IntentFilter List 集合, mReceivers是一个Map, key是BroadcastReceiver， value是ArrayList，集合为空就new一个然后放到Map中，然后把传进来的IntentFilter对象添加到List集合当中，从这几句代码可以看出来多个IntentFilter可以对应一个BroadcastReceiver；然后传递的IntentFilter action有可能有多个，循环遍历countActions，然后从mActions集合中通过get方法得到ReceiverRecord List集合, mActions是key为action，value为ArrayList的Map，就是说一个action可以对应多个ReceiverRecord对象，然后把刚才new的ReceiverRecord对象添加到ArrayList集合当中，注册方法就完了。

注册成功以后就要使用发送方法来发送广播
发送方法源码：

public boolean sendBroadcast(Intent intent) {
synchronized (mReceivers) {
final String action = intent.getAction();
final String type = intent.resolveTypeIfNeeded(
mAppContext.getContentResolver());
final Uri data = intent.getData();
final String scheme = intent.getScheme();
final Set categories = intent.getCategories();
final boolean debug = DEBUG || ((intent.getFlags() & Intent.FLAG_DEBUG_LOG_RESOLUTION) != 0);
if (debug)
Log.v(TAG, "Resolving type " + type + " scheme " + scheme + " of intent " + intent);
ArrayList entries = mActions.get(intent.getAction());
if (entries != null) {
if (debug) Log.v(TAG, "Action list: " + entries);
ArrayList receivers = null;
for (int i=0; i ReceiverRecord receiver = entries.get(i);
if (debug) Log.v(TAG, "Matching against filter " + receiver.filter);

if (receiver.broadcasting) {
if (debug) {
Log.v(TAG, " Filter's target already added");
}
continue;
}
int match = receiver.filter.match(action, type, scheme, data,categories, "LocalBroadcastManager");
if (match >= 0) {
if (debug) Log.v(TAG, " Filter matched! match=0x" + Integer.toHexString(match));

if (receivers == null) {
receivers = new ArrayList();
}
receivers.add(receiver);
receiver.broadcasting = true;
} else {
if (debug) {
String reason;
switch (match) {
case IntentFilter.NO_MATCH_ACTION:
reason = "action"; break;
case IntentFilter.NO_MATCH_CATEGORY:
reason = "category"; break;
case IntentFilter.NO_MATCH_DATA:
reason = "data"; break;
case IntentFilter.NO_MATCH_TYPE:
reason = "type"; break;
default:
reason = "unknown reason"; break;
}
Log.v(TAG, " Filter did not match: " + reason);
}
}
}
if (receivers != null) {
for (int i=0; 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;
}
}
}
return false;
}


方法的大致逻辑：首先 从mActions Map中根据intent的action得到ReceiverRecord List集合，然后循环集合得到单个ReceiverRecord 对象，如果ReceiverRecord 对象中的filter字段和intent中的属性匹配成功，那么就把该对象添加到新建的receivers List集合中; 最后把intent和receivers 集合封装成BroadcastRecord对象添加到mPendingBroadcasts List集合当中，然后通过handler发送消息，执行executePendingBroadcasts方法

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 BroadcastRecord br = brs[i];
for (int j=0; j br.receivers.get(j).receiver.onReceive(mAppContext, br.intent);
}
}
}
}


这个方法首先把mPendingBroadcasts的数据copy到BroadcastRecord[]数组当中，然后清空mPendingBroadcasts集合，循环遍历数组得到BroadcastRecord 对象，再循环BroadcastRecord 中的receivers集合得到单个ReceiverRecord对象，然后回调ReceiverRecord对象中BroadcastReceiver属性的onReceive方法，onReceive方法就是需要我们重写的方法。

有注册就有解绑，最后我们来看看解绑方法

public void unregisterReceiver(BroadcastReceiver receiver) {
synchronized (mReceivers) {
ArrayList filters = mReceivers.remove(receiver);
if (filters == null) {
return;
}
for (int i=0; i IntentFilter filter = filters.get(i);
for (int j=0; j String action = filter.getAction(j);
ArrayList receivers = mActions.get(action);
if (receivers != null) {
for (int k=0; k if (receivers.get(k).receiver == receiver) {
receivers.remove(k);
k--;
}
}
if (receivers.size() <= 0) {
mActions.remove(action);
}
}
}
}
}
}


首先从mReceivers Map中移除receiver，因为注册的时候放到Map中了，移除返回一个filters集合，然后循环遍历集合，得到filter中的action，在mActions Map中通过action得到receivers集合，这个集合中的单个ReceiverRecord对象的BroadcastReceiver属性如果和要解绑的BroadcastReceiver对象 一样，就移除这个ReceiverRecord对象，最后如果receivers集合中的对象都被移除了，那么就从mActions Map中移除当前的这个action。

到此主要的方法已经分析完毕，可以看出LocalBroadcastManager 内部实现主要依赖Map来保存，遍历，移除数据，是在单个App中进行的，所以以后大家在项目中需要广播的时候多使用本地广播。

谢谢阅读，如果大家感觉本文章对你有用，就麻烦点下喜欢。