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}:
* <ul>
* <li> You know that the data you are broadcasting won't leave your app, so
* don't need to worry about leaking private data.
* <li> 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.
* <li> It is more efficient than sending a global broadcast through the
* system.
* </ul>
*/
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<ReceiverRecord> receivers;
BroadcastRecord(Intent _intent, ArrayList<ReceiverRecord> _receivers) {
intent = _intent;
receivers = _receivers;
}
}
private static final String TAG =
"LocalBroadcastManager";
private static final boolean DEBUG =
false;
private final Context mAppContext;
private final HashMap<BroadcastReceiver, ArrayList<IntentFilter>> mReceivers
=
new HashMap<BroadcastReceiver, ArrayList<IntentFilter>>();
private final HashMap<String, ArrayList<ReceiverRecord>> mActions
=
new HashMap<String, ArrayList<ReceiverRecord>>();
private final ArrayList<BroadcastRecord> mPendingBroadcasts
=
new ArrayList<BroadcastRecord>();
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<IntentFilter> filters = mReceivers.get(receiver);
if (filters ==
null) {
filters =
new ArrayList<IntentFilter>(
1);
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);
}
}
}
/**
* Unregister a previously registered BroadcastReceiver. <em>All</em>
* 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<IntentFilter> filters = mReceivers.remove(receiver);
if (filters ==
null) {
return;
}
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) {
receivers.remove(k);
k--;
}
}
if (receivers.size() <=
0) {
mActions.remove(action);
}
}
}
}
}
}
/**
* Broadcast the given intent to all interested BroadcastReceivers. This
* call is asynchronous; it returns immediately, and you will continue
* executing while the receivers are run.
*
* @param intent The Intent to broadcast; all receivers matching this
* Intent will receive the broadcast.
*
* @see #registerReceiver
*/
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<String> 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<ReceiverRecord> entries = mActions.get(intent.getAction());
if (entries !=
null) {
if (debug) Log.v(TAG,
"Action list: " + entries);
ArrayList<ReceiverRecord> receivers =
null;
for (
int i=
0; i<entries.size(); 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<ReceiverRecord>();
}
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.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;
}
}
}
return false;
}
/**
* Like {@link #sendBroadcast(Intent)}, but if there are any receivers for
* the Intent this function will block and immediately dispatch them before
* returning.
*/
public void sendBroadcastSync(Intent intent) {
if (sendBroadcast(intent)) {
executePendingBroadcasts();
}
}
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<brs.length; i++) {
BroadcastRecord br = brs[i];
for (
int j=
0; j<br.receivers.size(); j++) {
br.receivers.get(j).receiver.onReceive(mAppContext, br.intent);
}
}
}
}
}
LocalBroadcastManager中有三个关键字段分别为:
private final HashMap<BroadcastReceiver, ArrayList<IntentFilter>> mReceivers =
new HashMap();
private final HashMap<String, ArrayList<ReceiverRecord>> mActions =
new HashMap();
private final ArrayList<BroadcastRecord> mPendingBroadcasts =
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<IntentFilter>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<ReceiverRecord>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);
ArrayList<IntentFilter> filters = mReceivers.get(receiver);
if (filters ==
null) {
filters =
new ArrayList<IntentFilter>(
1);
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);
}
}
}
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
“`java
public void unregisterReceiver(BroadcastReceiver receiver) {
synchronized (mReceivers) {
ArrayList<IntentFilter> filters = mReceivers.remove(receiver);
if (filters == null) {
return;
}
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) {
receivers.remove(k);
k--;
}
}
if (receivers.size() <= 0) {
mActions.remove(action);
}
}
}
}
}
}
““
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 Set<String> 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<ReceiverRecord> entries = mActions.get(intent.getAction());
if (entries !=
null) {
if (debug) Log.v(TAG,
"Action list: " + entries);
ArrayList<ReceiverRecord> receivers =
null;
for (
int i=
0; i<entries.size(); 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<ReceiverRecord>();
}
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.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;
}
}
}
return false;
}
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; i<brs.length; i++) {
BroadcastRecord br = brs[i];
for (
int j=
0; j<br.receivers.size(); j++) {
br.receivers.get(j).receiver.onReceive(mAppContext, br.intent);
}
}
}
}
mPendingBroadcasts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.
