android - 在 LocalBroadcastManager 注册的 BroacastReceiver 的 onReceive() 在哪个线程运行？

Question

我在首选项 Activity 中注册了一个广播接收器，并从(清醒的)IntentService 向它发送(同步)广播。显然 onReceive 在服务的线程上运行。这是我的错吗？是否记录了行为？

偏好 Activity :

public final class SettingsActivity extends BaseSettings {

    private static CharSequence sMasterKey;
    private CheckBoxPreference mMasterPref;
    // Receiver
    /** If the master preference is changed externally this reacts */
    private BroadcastReceiver mExternalChangeReceiver =
        new ExternalChangeReceiver();

    public static void notifyMonitoringStateChange(Context ctx,
            CharSequence action, boolean isToggling) {
        final LocalBroadcastManager lbm = LocalBroadcastManager
            .getInstance(ctx);
        Intent intent = new Intent(ctx, ExternalChangeReceiver.class);
        intent.setAction(action.toString());
        intent.putExtra(TOGGLING_MONITORING_IN_PROGRESS, isToggling);
        lbm.sendBroadcastSync(intent);
    }

    @Override
    protected void onStart() {
        super.onStart();
        final LocalBroadcastManager lbm = LocalBroadcastManager
            .getInstance(this);
        lbm.registerReceiver(mExternalChangeReceiver, new IntentFilter(
            ac_toggling.toString()));
    }

    @Override
    protected void onStop() {
        // may not be called in Froyo
        final LocalBroadcastManager lbm = LocalBroadcastManager
            .getInstance(this);
        lbm.unregisterReceiver(mExternalChangeReceiver);
        super.onStop();
    }

    private final class ExternalChangeReceiver extends BroadcastReceiver {

        ExternalChangeReceiver() {}

        @Override
        @SuppressWarnings("synthetic-access")
        public void onReceive(Context ctx, Intent intent) {
            if (sMasterKey == null || mMasterPref == null) return; // if
            // onPostReceive has not run this will be null
            final String action = intent.getAction();
            if (ac_toggling.equals(action)) {
                final boolean isToggling = intent.getBooleanExtra(
                    TOGGLING_MONITORING_IN_PROGRESS, false);
                Log.w(ExternalChangeReceiver.class.getSimpleName(),
                    "isToggling " + isToggling);
                mMasterPref.setEnabled(!isToggling); // line 168 !!!
                refreshMasterPreference(isToggling);
            }
        }
    }
}

Intent 服务(位置监控):

SettingsActivity.notifyMonitoringStateChange(this, ac_toggling, true);

异常(E/AndroidRuntime):

FATAL EXCEPTION: IntentService[LocationMonitor]
android.view.ViewRootImpl$CalledFromWrongThreadException: Only the original thread that created a view hierarchy can touch its views.
    at android.view.ViewRootImpl.checkThread(ViewRootImpl.java:4746)
    at android.view.ViewRootImpl.requestLayout(ViewRootImpl.java:823)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.view.View.requestLayout(View.java:15473)
    at android.widget.AbsListView.requestLayout(AbsListView.java:1819)
    at android.widget.AdapterView$AdapterDataSetObserver.onChanged(AdapterView.java:813)
    at android.widget.AbsListView$AdapterDataSetObserver.onChanged(AbsListView.java:5958)
    at android.database.DataSetObservable.notifyChanged(DataSetObservable.java:37)
    at android.widget.BaseAdapter.notifyDataSetChanged(BaseAdapter.java:50)
    at android.preference.PreferenceGroupAdapter.onPreferenceChange(PreferenceGroupAdapter.java:238)
    at android.preference.Preference.notifyChanged(Preference.java:1099)
    at android.preference.Preference.setEnabled(Preference.java:726)
    at gr.uoa.di.monitoring.android.activities.SettingsActivity$ExternalChangeReceiver.onReceive(SettingsActivity.java:168)
    at android.support.v4.content.LocalBroadcastManager.executePendingBroadcasts(LocalBroadcastManager.java:297)
    at android.support.v4.content.LocalBroadcastManager.sendBroadcastSync(LocalBroadcastManager.java:278)
    at gr.uoa.di.monitoring.android.activities.SettingsActivity.notifyMonitoringStateChange(SettingsActivity.java:54)
    at gr.uoa.di.monitoring.android.services.Monitor.abort(Monitor.java:241)
    at gr.uoa.di.monitoring.android.services.LocationMonitor.doWakefulWork(LocationMonitor.java:103)
    at com.commonsware.cwac.wakeful.WakefulIntentService.onHandleIntent(WakefulIntentService.java:94)
    at android.app.IntentService$ServiceHandler.handleMessage(IntentService.java:65)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.os.HandlerThread.run(HandlerThread.java:60)

在模拟器 API 17 上

Answer 1

sendBroadcastSync() 确实在调用它的线程上运行(除非正在进行竞争)。它的实现should be :

public void sendBroadcastSync(Intent intent) { // directly calls executePendingBroadcasts
        if (sendBroadcast(intent)) {
            executePendingBroadcasts();
        }
}

我不确定的比赛部分通过 sendBroadcast() 调用进入，如果它找到任何匹配的接收者(为此 Intent 向 LBM 注册)，发送消息后返回 true到私有(private)处理程序与主循环相关联 - 缩写:

@Override
public boolean sendBroadcast(Intent intent) {
    synchronized (mReceivers) {
        final String action = intent.getAction();
        final ArrayList<ReceiverRecord> entries = mActions.get(action);
        if (entries == null) return false; // no receivers for that action
        ArrayList<ReceiverRecord> receivers = new ArrayList<ReceiverRecord>();
        for (ReceiverRecord receiver : entries) {
            if (receiver.broadcasting) continue;
            // match the intent
            int match = receiver.filter.match(action,
                intent.resolveTypeIfNeeded(mAppContext.getContentResolver()),
                intent.getScheme(), intent.getData(),
                intent.getCategories(), "LocalBroadcastManager");
            if (match >= 0) {
                receivers.add(receiver);
                receiver.broadcasting = true;
            }
        }
        final int size = receivers.size();
        if (size == 0) return false; // no receivers for this intent
        for (int i = 0; i < 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;
    }
}

哪里:

    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);
            }
        }

我不确定主线程和正在执行的线程 sendBroadcastSync() 之间是否存在竞争 - 所以 executePendingBroadcasts() 将在主线程上运行线。如果不是，则 executePendingBroadcasts() 在线程上运行 sendBroadcastSync 并运行 directly calls接收者的onReceive

有一天我应该研究为什么(在 executePendingBroadcasts 中)synchronized(mReceivers) 而不是 synchronized(mPendingBroadcasts)。