Android中收到短信等事件都是通过广播发送给应用程序的，360手机卫士等程序都是通过注
册高优先级的BroadcastReceiver来实现短信防火墙等功能。对于我们来说很想知道系统中都有
哪些程序注册了BroadcastReceiver，但是通过什么方法能获取系统BroadcastReceiver的列
表呢？

      我在群里问了一下，他们告诉我的答案居然是分析所有apk的AndroidManifest.xml，再加上
解析dex里面的动态注册！而这根本不是我想达到的目的，我要知道的是目前系统中实时的
BroadcastReceiver，而不是通过静态分析得到。于是我开始看Android Framework代码，想
搞清楚广播的实现机制到底是怎样的。

      注册BroadcastReceiver的过程是这样的：Activity调用registerReceiver，然后经过几层
内部类接口的调用之后，通过Binder机制与ActivityManagerService通信，而
ActivityManagerService里有一个ReceiverList保存着系统所有的BroadcastReceiver。

      发送广播的过程是：Activity向ActivityManagerService发送广播，
ActivityManagerService查找ReceiverList，通过比对IntentFilter找到所有对应的
BroadcastReceiver，根据BroadcastReceiver的优先级进行排序后，扔进广播发送队列里。
而后由专门的线程负责投递广播消息。


      大致的过程就是这样的，那么目标就是获取ActivityManagerService中的ReceiverList。
一开始我想的办法是：因为ActivityManagerService是一个单独的进程（system_server），
我们可以通过注入system_server进程来获得ReceiverList。但是由于
ActivityManagerService是java实现的，无法直接获得ReceiverList，要解析java的数据结构
难度就太大了。
      于是又再次查看
frameworks/base/services/java/com/android/server/am/ActivityManagerService.java：

public final class ActivityManagerService extends ActivityManagerNative
		implements Watchdog.Monitor, BatteryStatsImpl.BatteryCallback {
	......

	private final int broadcastIntentLocked(ProcessRecord callerApp,
			String callerPackage, Intent intent, String resolvedType,
			IIntentReceiver resultTo, int resultCode, String resultData,
			Bundle map, String requiredPermission,
			boolean ordered, boolean sticky, int callingPid, int callingUid) {
		intent = new Intent(intent);

		......

		// Figure out who all will receive this broadcast.
		List receivers = null;
		List<BroadcastFilter> registeredReceivers = null;
		try {
			if (intent.getComponent() != null) {
				......
			} else {
				......
				registeredReceivers = mReceiverResolver.queryIntent(intent, resolvedType, false);
			}
		} catch (RemoteException ex) {
			......
		}

		final boolean replacePending =
			(intent.getFlags()&Intent.FLAG_RECEIVER_REPLACE_PENDING) != 0;

		int NR = registeredReceivers != null ? registeredReceivers.size() : 0;
		if (!ordered && NR > 0) {
			// If we are not serializing this broadcast, then send the
			// registered receivers separately so they don't wait for the
			// components to be launched.
			BroadcastRecord r = new BroadcastRecord(intent, callerApp,
				callerPackage, callingPid, callingUid, requiredPermission,
				registeredReceivers, resultTo, resultCode, resultData, map,
				ordered, sticky, false);
			......
			boolean replaced = false;
			if (replacePending) {
				for (int i=mParallelBroadcasts.size()-1; i>=0; i--) {
					if (intent.filterEquals(mParallelBroadcasts.get(i).intent)) {
						......
						mParallelBroadcasts.set(i, r);
						replaced = true;
						break;
					}
				}
			}

			if (!replaced) {
				mParallelBroadcasts.add(r);

				scheduleBroadcastsLocked();
			}

			registeredReceivers = null;
			NR = 0;
		}

		......

	}

	......
}

      看这一句：

registeredReceivers = mReceiverResolver.queryIntent(intent, resolvedType, false); 

到frameworks\base\services\java\com\android\server\IntentReslover.java中，注意到一个特性：

public List<R> queryIntent(Intent intent, String resolvedType, boolean defaultOnly) {
        String scheme = intent.getScheme();

        ArrayList<R> finalList = new ArrayList<R>();

        final boolean debug = localLOGV ||
                ((intent.getFlags() & Intent.FLAG_DEBUG_LOG_RESOLUTION) != 0);

        if (debug) Slog.v(
            TAG, "Resolving type " + resolvedType + " scheme " + scheme
            + " of intent " + intent);
       sortResults(finalList);
............
        if (debug) {
            Slog.v(TAG, "Final result list:");
            for (R r : finalList) {
                Slog.v(TAG, "  " + r);
            }
        }
        return finalList;
    }

      这个有个debug选项可以打印出最终获得的ReceiverList，还是按照优先级排过序的有木有？

      于是乎获取接收器列表就太简单了，只需要三行代码即可：

    	Intent intent = new Intent("android.provider.Telephony.SMS_RECEIVED");
    	intent.addFlags(Intent.FLAG_DEBUG_LOG_RESOLUTION);
        sendBroadcast(intent);

      重点就是第二句，设置了FLAG_DEBUG_LOG_RESOLUTION，这样就会在LogCat中打印
出所有注册了android.provider.Telephony.SMS_RECEIVED的BroadcastReceiver。用
IntentResolver作为TAG过滤一下看起来更方便：

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