我有一个带按钮的片段。单击时，它会告诉服务启动轮询传感器，然后将传感器数据插入后台线程的数据库中。再次按下该按钮时，服务将停止。按下“停止”按钮时，执行程序队列中仍可能有插入数据库的任务，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));
}
}
}
第一次单击该按钮时，将启动以下服务：
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
}
}
所以我想按下第二个按钮显示对话框。然后再次按下它，服务将停止，我想等到队列清除，然后将一个解除事件发送回片段以关闭进度对话框。
显示对话框很简单。我可以在调用onClick之前在片段的stopService方法中添加进度对话框代码
我很难弄清楚如何在onDestroy的{{1}}中发回消息以解除该对话
如果不借助外部库，最好的方法是什么？
我可以使用SensorService BroadcastReceiver中使用的SensorService吗？或者最好在片段中创建一个新的Handler，以某种方式将传递给服务，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内容：
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MessageHandler的新实例（尝试将其放置在各种位置......结果相同）：
public static Handler messageHandler = new MessageHandler();
然后使用以下命令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中，我创建了messageHandler：
Bundle extras = intent.getExtras();
messageHandler = (Messenger) extras.get("MESSENGER");
然后我会在SensorService onDestroy：
sendMessage("SHOW");
并在同一方法的最后解雇它：
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();
}
}
所以我可以启动服务，但是当我再次按下它停止时，我明白了：
java.lang.RuntimeException：无法停止服务com.example.app.SensorService@21124f0：java.lang.NullPointerException：尝试调用虚方法'void android.os.Messenger.send（android.os.Message） '在空对象引用上
并且引用SensorService的第105行，其中messageHandler.send(message)
关于可能出错的想法？
答案 0 :(得分：3)
活动：
protected BroadcastReceiver mMessageReceiver = new BroadcastReceiver() {
@Override
public void onReceive(Context context, final Intent intent) {
runOnUiThread(new Runnable() {
@Override
public void run() {
if(intent.hasExtra("someExtraMessage")){
doSomething(intent.getStringExtra("someExtraMessage"));
}
}
});
}
};
@Override
public void onCreate(Bundle savedInstanceState, PersistableBundle persistentState) {
super.onCreate(savedInstanceState, persistentState);
LocalBroadcastManager.getInstance(this).registerReceiver(mMessageReceiver,
new IntentFilter("message-id"));
}
protected void onDestroy() {
super.onDestroy();
LocalBroadcastManager.getInstance(this).unregisterReceiver(mMessageReceiver);
}
public void doSomething(){
//...
}
然后从服务的某处：
Context context = BamBamApplication.getApplicationContext(); // Can be application or activity context.
// BamBamApplicaiton extends Application ;)
Intent intent = new Intent("message-id");
intent.putExtra("someExtraMessage", "Some Message :)");
LocalBroadcastManager.getInstance(context).sendBroadcast(intent);
实际上你从一开始就做错了:)所有服务都在主线程上运行，所以在这里你必须更好地开始所有硬处理到异步任务来在后台移动它，否则你会卡住你的应用程序，或者你会突然意外崩溃。
以下是异步任务的示例，该异常任务在后台解析json api响应，并使用参数类型化结果。
class ParseJsonInBackground<T> extends AsyncTask<String, Void, ApiResponseModel<T>> {
private ProcessResponse<T> func;
private Type inClass;
public ParseJsonInBackground(ProcessResponse<T> f, Type inClass){
this.func = f;
this.inClass = inClass;
}
@Override
protected void onPreExecute() {
super.onPreExecute();
}
@Override
protected ApiResponseModel<T> doInBackground(String... json) {
Gson gson = new Gson();
try {
ApiResponseModel<T> result = (ApiResponseModel<T>) gson.fromJson(json[0], inClass);
return result;
}catch(Exception e){
ApiResponseModel<T> result = new ApiResponseModel<T>();
result.data = null;
result.success = false;
result.error = new ArrayList<>();
result.error.add(new ErrorModel(0, "Parsing error", "Parsing error"));
return result;
}
}
@Override
protected void onPostExecute(ApiResponseModel<T> result) {
Utils.hideLoadingProgress(mContext);
if(result != null && func != null){
if(result.success){
func.onSuccess(result);
}else{
func.onError(result);
}
}
}
}
并示例如何调用：
new ParseJsonInBackground<T>(responseFunc, inClass).execute(json.toString());
答案 1 :(得分：0)
我建议通过Handler消息执行此操作：您将服务中的消息发送到您的Activity，该消息必须注册为回调处理程序（实现http://developer.android.com/reference/android/os/Handler.Callback.html）。使用自定义消息代码（message.what）并监听它。请记住将此信息发送到您应用程序的主循环器（来自服务）。
您还可以查看此评论，其中说明了与更多代码的此类互动：https://stackoverflow.com/a/20595215/4310905
答案 2 :(得分：0)
It turns out that the code in the Edit of my original question works, but I have to shuffle around some of my code:
Bundle extras = intent.getExtras();
messageHandler = (Messenger) extras.get("MESSENGER");
The above needs to be moved to onStartCommand of SensorService instead of being in the BroadcastReceiver