android - AlarmManager、BroadcastReceiver 和服务不工作

Question

我正在重构一些代码，以便我的应用程序每天在给定时间从网站提取一次数据。根据我的研究，AlarmManager 似乎是最合适的方法。

我一直关注的教程是:http://mobile.tutsplus.com/tutorials/android/android-fundamentals-downloading-data-with-services/

到目前为止，AlarmManager 和 BroadcastReceiver 似乎在工作，但是 Service 似乎从未启动(即 onStartCommand 好像没有调用)

以下是我目前拥有的代码的重要 fragment :

MyActivity.java

private void setRecurringAlarm(Context context) {
    Calendar updateTime = Calendar.getInstance();
    updateTime.setTimeZone(TimeZone.getDefault());
    updateTime.set(Calendar.HOUR_OF_DAY, 20);
    updateTime.set(Calendar.MINUTE, 30);

    Intent downloader = new Intent(context, AlarmReceiver.class);
    downloader.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    PendingIntent pendingIntent = PendingIntent.getBroadcast(context, 0, downloader, PendingIntent.FLAG_CANCEL_CURRENT);
    AlarmManager alarmManager = (AlarmManager) getSystemService(Context.ALARM_SERVICE);
    // should be AlarmManager.INTERVAL_DAY (but changed to 15min for testing)
    alarmManager.setRepeating(AlarmManager.RTC_WAKEUP, updateTime.getTimeInMillis(), AlarmManager.INTERVAL_FIFTEEN_MINUTES, pendingIntent); 
    Log.d("MyActivity", "Set alarmManager.setRepeating to: " + updateTime.getTime().toLocaleString());
}

AlarmReceiver.java

public class AlarmReceiver extends BroadcastReceiver {
    @Override
    public void onReceive(Context context, Intent intent) {
        Intent dailyUpdater = new Intent(context, MyService.class);
        context.startService(dailyUpdater);
        Log.d("AlarmReceiver", "Called context.startService from AlarmReceiver.onReceive");
    }
}

MyService.java

public class MyService extends Service {

    @Override
    public int onStartCommand(Intent intent, int flags, int startId) {
        Log.d("MyService", "About to execute MyTask");
        new MyTask().execute();
        return Service.START_FLAG_REDELIVERY;
    }

    @Override
    public IBinder onBind(Intent intent) {
        return null;
    }

    private class MyTask extends AsyncTask<String, Void, boolean> {
        @Override
        protected boolean doInBackground(String... strings) {
            Log.d("MyService - MyTask", "Calling doInBackground within MyTask");
            return false;
        }
    }
}

AndroidManifest.xml

<application ...>
    ...
    <service android:name="MyService"></service>
    <receiver android:name="AlarmReceiver"></receiver>
</application>

当我在 MyActivity 中触发 setRecurringAlarm 时，日志会按预期打印，同样地，每隔 15 分钟就会出现来自 AlarmReceiver 的日志。但是，我从未看到来自 MyService 的日志 :(

我在日志中看到的示例:

DEBUG/MyActivity(688): Set alarmManager.setRepeating to: Jan 29, 2012 8:30:06 PM
DEBUG/AlarmReceiver(688): Called context.startService from AlarmReceiver.onReceive
DEBUG/AlarmReceiver(688): Called context.startService from AlarmReceiver.onReceive

似乎无法弄清楚我做错了什么 - 我对 Android Dev Docs 的理解是在 AlarmReceiver 中，当我调用 context.startService(dailyUpdater) 时，它应该依次调用 MyService 中的 onStartCommand，尽管事实并非如此!

我做错了什么导致 MyService 根本无法启动？

Answer 1

想通了!

MyService 应该扩展 IntentService 而不是 Service!

有了这个变化，这也意味着应该覆盖 onHandleIntent 而不是覆盖 onStartCommand(参见 IntentService 上的文档)

所以 MyService 现在看起来像这样:

public class MyService extends IntentService {

    public MyService() {
        super("MyServiceName");
    }

    @Override
    protected void onHandleIntent(Intent intent) {
        Log.d("MyService", "About to execute MyTask");
        new MyTask().execute();
    }

    private class MyTask extends AsyncTask<String, Void, boolean> {
        @Override
        protected boolean doInBackground(String... strings) {
            Log.d("MyService - MyTask", "Calling doInBackground within MyTask");
            return false;
        }
    }
}

注意:根据文档，onBind 的默认实现返回 null，因此无需覆盖它。

有关扩展 IntentService 的更多信息:http://developer.android.com/guide/topics/fundamentals/services.html#ExtendingIntentService