LocalBroadcastManager源码分析

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.