【发布时间】：2016-04-20 05:07:45
【问题描述】：
我有一个带按钮的片段。单击它时，它会告诉服务开始轮询传感器，然后将传感器数据插入后台线程上的数据库中。再次按下按钮时，服务将停止。当按下停止按钮时，执行程序队列中可能仍有任务正在插入数据库，因此在此期间我想显示一个进度对话框，并在整个队列清除后将其关闭。带有按钮的片段如下所示：
public class StartFragment extends Fragment implements View.OnClickListener {
Button startButton;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.fragment_start, container, false);
startButton = (Button) view.findViewById(R.id.startButton);
startButton.setOnClickListener(this);
return view;
}
@Override
public void onClick(View v) {
if (recording has not yet started){
mainActivity.startService(new Intent(mainActivity, SensorService.class));
} else {
//I want to display a progress dialog here when the service is told to stop
//Once all executor task queue is clear, I want to dismiss this dialog
mainActivity.stopService(new Intent(mainActivity, SensorService.class));
}
}
}
当第一次点击按钮时，会启动以下服务：
public class SensorService extends Service implements SensorEventListener {
public static final int SCREEN_OFF_RECEIVER_DELAY = 100;
private SensorManager sensorManager = null;
private WakeLock wakeLock = null;
ExecutorService executor;
Runnable insertHandler;
private void registerListener() {
//register 4 sensor listeners (acceleration, gyro, magnetic, gravity)
}
private void unregisterListener() {
sensorManager.unregisterListener(this);
}
public BroadcastReceiver receiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, Intent intent) {
Log.i(TAG, "onReceive("+intent+")");
if (!intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
return;
}
Runnable runnable = new Runnable() {
public void run() {
Log.i(TAG, "Runnable executing...");
unregisterListener();
registerListener();
}
};
new Handler().postDelayed(runnable, SCREEN_OFF_RECEIVER_DELAY);
}
};
public void onSensorChanged(SensorEvent event) {
//get sensor values and store into 4 different arrays here
//insert into database in background thread
executor.execute(insertHandler);
}
@Override
public void onCreate() {
super.onCreate();
//get sensor manager and sensors here
PowerManager manager = (PowerManager) getSystemService(Context.POWER_SERVICE);
wakeLock = manager.newWakeLock(PowerManager.PARTIAL_WAKE_LOCK, TAG);
registerReceiver(receiver, new IntentFilter(Intent.ACTION_SCREEN_OFF));
//Executor service and runnable for DB inserts
executor = Executors.newSingleThreadExecutor();
insertHandler = new InsertHandler();
}
@Override
public IBinder onBind(Intent intent) {
return null;
}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
super.onStartCommand(intent, flags, startId);
startForeground(Process.myPid(), new Notification());
registerListener();
wakeLock.acquire();
return START_STICKY;
}
@Override
public void onDestroy() {
//Prevent new tasks from being added to thread
executor.shutdown();
try {
//Wait for all tasks to finish before we proceed
while (!executor.awaitTermination(1, TimeUnit.SECONDS)) {
Log.i(TAG, "Waiting for current tasks to finish");
}
} catch (InterruptedException e) {
executor.shutdownNow();
Thread.currentThread().interrupt();
}
if (executor.isTerminated()){
//Stop everything else once the task queue is clear
unregisterReceiver(receiver);
unregisterListener();
wakeLock.release();
dbHelper.close();
stopForeground(true);
//Once the queue is clear, I want to send a message back to the fragment to dismiss the progress dialog here
}
}
class InsertHandler implements Runnable {
public void run() {
//get sensor values from 4 arrays, and insert into db here
}
}
所以我想在第二次按下按钮时显示对话框。然后一旦再次按下，服务将停止，我想等到队列清空，然后将关闭事件发送回片段以关闭进度对话框。
显示对话框很容易。我可以在片段的onClick 方法中添加进度对话框代码，在调用stopService 之前
我很难弄清楚如何在SensorService 的onDestroy 中发回消息以关闭该对话框
不求助于外部库的最佳方法是什么？
有什么方法可以使用我在SensorService 中使用的BroadcastReceiver 吗？或者最好在片段中创建一个新的Handler，然后以某种方式将其传递给服务，以便它可以将消息发送回片段？
编辑：
我根据以下答案之一尝试了以下方法：
在我的片段类中添加了MessageHandler 类：
public static class MessageHandler extends Handler {
@Override
public void handleMessage(Message message) {
int state = message.arg1;
switch (state) {
case 0:
stopDialog.dismiss();
break;
case 1:
stopDialog = new ProgressDialog(mainActivity);
stopDialog.setMessage("Stopping...");
stopDialog.setTitle("Saving data");
stopDialog.setProgressNumberFormat(null);
stopDialog.setCancelable(false);
stopDialog.setMax(100);
stopDialog.show();
break;
}
}
}
在我的片段中创建了一个 MessageHandler 的新实例（尝试将其放置在不同的地方......结果相同）：
public static Handler messageHandler = new MessageHandler();
然后使用以下代码从我的片段启动服务：
Intent startService = new Intent(mainActivity, SensorService.class);
startService.putExtra("MESSENGER", new Messenger(messageHandler));
getContext().startService(startService);
在我的SensorService BroadcastReceiver 我创建了messageHandler：
Bundle extras = intent.getExtras();
messageHandler = (Messenger) extras.get("MESSENGER");
然后我在SensorServiceonDestroy的开头显示对话框：
sendMessage("SHOW");
并在同一方法的最后关闭它：
sendMessage("HIDE");
我的sendMessage 方法如下所示：
public void sendMessage(String state) {
Message message = Message.obtain();
switch (state) {
case "SHOW":
message.arg1 = 1;
break;
case "HIDE" :
message.arg1 = 0;
break;
}
try {
messageHandler.send(message);
} catch (RemoteException e) {
e.printStackTrace();
}
}
这样我就可以启动服务了，但是当我再次按下它停止时，我得到了这个：
java.lang.RuntimeException：无法停止服务 com.example.app.SensorService@21124f0：java.lang.NullPointerException：尝试调用虚拟方法 'void android.os.Messenger.send(android.os.Message) ' 在空对象引用上
它指的是SensorService的第105行，我有messageHandler.send(message)
想到什么可能是错的？
【问题讨论】：
-
您为什么要尝试将消息发送回片段？你不能只在
onDestroy的开头显示对话框，然后在onDestroy的结尾关闭它吗？ -
刚看到this question/answers看看吧。
-
我无法在
onDestroy中显示对话框，因为那在服务中并且不在 UI 线程中操作
标签： android android-fragments android-service android-dialog android-handler