LocalBroadcastManager优势:
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 {@link android.content.Context#sendBroadcast}:
- 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.
相对于BroadcastReceiver来说,LocalBroadcastManager有如下优势:
- 发送的广播只会在当前APP中传播,不会泄露给其他APP,确保数据传输的安全性.
- 其他APP的广播无法发送到本地APP中,不用担心安全漏洞被其他APP利用.
- 比系统全局广播更加高效.
LocalBraodcastManager源码如下:
/**
* 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 {@link android.content.Context#sendBroadcast}:
*
* - 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.
*
*/
public final class LocalBroadcastManager {
private static class ReceiverRecord {
final IntentFilter filter;
final BroadcastReceiver receiver;
boolean broadcasting;
ReceiverRecord(IntentFilter _filter, BroadcastReceiver _receiver) {
filter = _filter;
receiver = _receiver;
}
@Override
public String toString() {
StringBuilder builder = new StringBuilder(128);
builder.append("Receiver{");
builder.append(receiver);
builder.append(" filter=");
builder.append(filter);
builder.append("}");
return builder.toString();
}
}
private static class BroadcastRecord {
final Intent intent;
final ArrayList receivers;
BroadcastRecord(Intent _intent, ArrayList _receivers) {
intent = _intent;
receivers = _receivers;
}
}
private static final String TAG = "LocalBroadcastManager";
private static final boolean DEBUG = false;
private final Context mAppContext;
private final HashMap> mReceivers
= new HashMap>();
private final HashMap> mActions
= new HashMap>();
private final ArrayList mPendingBroadcasts
= new ArrayList();
static final int MSG_EXEC_PENDING_BROADCASTS = 1;
private final Handler mHandler;
private static final Object mLock = new Object();
private static LocalBroadcastManager mInstance;
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);
}
}
};
}
/**
* Register a receive for any local broadcasts that match the given IntentFilter.
*
* @param receiver The BroadcastReceiver to handle the broadcast.
* @param filter Selects the Intent broadcasts to be received.
*
* @see #unregisterReceiver
*/
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);
}
}
}
/**
* Unregister a previously registered BroadcastReceiver. All
* filters that have been registered for this BroadcastReceiver will be
* removed.
*
* @param receiver The BroadcastReceiver to unregister.
*
* @see #registerReceiver
*/
public void unregisterReceiver(BroadcastReceiver receiver) {
synchronized (mReceivers) {
ArrayList filters = mReceivers.remove(receiver);
if (filters == null) {
return;
}
for (int i=0; i receivers = mActions.get(action);
if (receivers != null) {
for (int k=0; k 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= 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 -
LocalBroadcastManager中有三个关键字段分别为:private final HashMapmPendingBroadcasts = new ArrayList(); HashMap对象的mReceivers存储广播和过滤信息集合,通过以BroadcastReceiver为Key,ArrayList为Value,这样做是为了方便注销.HashMap对象的mActions存储Action和ReceiverRecord,以Action为key,ArrayList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他的BroadcastReceiver.mPendingBroadcasts就是发送广播的集合. -
LocalBroadcastManager的构造函数: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); } } }; }LocalBroadcastManager的构造函数很简单,就做了一件事,创建一个基于主线程Looper的Handler,并接收msg.what为MSG_EXEC_PENDING_BROADCASTS的消息,并调用executePendingBroadcasts()发送广播.
-
LocalBroadcastManager注册public void registerReceiver(BroadcastReceiver receiver, IntentFilter filter) { synchronized (mReceivers) { ReceiverRecord entry = new ReceiverRecord(filter, receiver); ArrayListfilters = mReceivers.get(receiver); if (filters == null) { filters = new ArrayList (1); mReceivers.put(receiver, filters); } filters.add(filter); for (int i=0; i (1); mActions.put(action, entries); } entries.add(entry); } } } 基于要注册的BroadReceiver和IntentFilter,在mReceivers中查找,如果为null,便把传过来的receiver和filter参数存储到mReceivers中,同时将IntentFilter中的Action存储到mActions中.方便后面注销广播,对元素的移除.
-
LocalBroadcastManager的注销public void unregisterReceiver(BroadcastReceiver receiver) { synchronized (mReceivers) { ArrayListfilters = mReceivers.remove(receiver); if (filters == null) { return; } for (int i=0; i LocalBroadcastManager注销就是从mReceivers和mActions中移除相应的元素,比如BroadcastReceiver和IntentFilter以及Action. -
LocalBroadcastManager发送广播: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 Setcategories = 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 (); } 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 先根据Action从mActions中取出ReceiverRecord列表,遍历ReceiverRecord判断filter和intent中的action,type,scheme,data,category是否匹配,是的话保存到receivers列表中,发送msg.what为MSG_EXEC_PENDING_BROADCASTS的消息,通过主线程的Handler去处理.
-
LocalBroadcastManager处理消息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; imPendingBroadcasts转换为数组
BroadcastRecord,循环遍历每个receiver,调用其onReceive函数,完成消息的传递.
LocalBroadcastManager分析总结:
-
LocalBroadcastManager的核心思想还是Handler,只是利用了IntentFilter的match功能,至于BroadcastReceiver换成其他接口也无所谓,只是顺便利用了现成的类和概念而已. - 因为是Handler通讯,所以才有实现了应用内通讯,自然安全性高,效率高.