Flashlight turns off when other apps are started. Android

问题

I am working on Flashlight app with Widget. When I turn on Flashlight with Widget flashlight is on, and when I start some app, the flashlight turns off. Why is this happening? Why can't my Flashlight run in background? How can I prevent this? I want Flashlight to be turned off only by user not the system.

This is my code for widget:

    @Override
    public void onReceive(Context context, Intent intent) {
        RemoteViews views = new RemoteViews(context.getPackageName(),
                R.layout.widget_layout);
        myPref = PreferenceManager.getDefaultSharedPreferences(context);
        if (AppGlobals.getIsFlashOn()) {
            views.setImageViewResource(R.id.flashlight_widget_imageview,
                    R.drawable.light_on);
        } else {
            views.setImageViewResource(R.id.flashlight_widget_imageview,
                    R.drawable.light_off);
        }

        AppWidgetManager appWidgetManager = AppWidgetManager
                .getInstance(context);
        appWidgetManager.updateAppWidget(new ComponentName(context,
                FlashlightWidgetProvider.class), views);

        if (AppGlobals.getIsFlashOn()) {
            if (getmCameraWidget() != null) {
                flashOffWidget();

            }

            if (Flashlight.getmCameraActivity() != null) {

                flashOffApp();
                Flashlight.flashlight_button
                        .setBackgroundResource(R.drawable.light_on);

            }

            Flashlight.turnMotorolaOff();
            isLightOn = false;
            NotifyFlashlight(context, isLightOn);

        } else {
            try {
                setmCameraWidget(Camera.open());
            } catch (Exception e) {
                e.printStackTrace();
            }

            if (getmCameraWidget() == null) {
            } else {
                setParamsWidget(getmCameraWidget().getParameters());

                List<String> flashModes = getParamsWidget()
                        .getSupportedFlashModes();

                if (flashModes == null) {
                    return;
                } else {
                    if (count == 0) {
                        getParamsWidget().setFlashMode(
                                Parameters.FLASH_MODE_OFF);
                        getmCameraWidget().setParameters(getParamsWidget());
                        getmCameraWidget().startPreview();
                        AppGlobals.setIsFlashOn(true);
                    }

                    String flashMode = getParamsWidget().getFlashMode();

                    if (!Parameters.FLASH_MODE_TORCH.equals(flashMode)) {

                        if (flashModes.contains(Parameters.FLASH_MODE_TORCH)) {
                            getParamsWidget().setFlashMode(
                                    Parameters.FLASH_MODE_TORCH);
                            getmCameraWidget().setParameters(getParamsWidget());
                        } else {
                            getParamsWidget().setFlashMode(
                                    Parameters.FLASH_MODE_ON);

                            getmCameraWidget().setParameters(getParamsWidget());
                            try {
                                getmCameraWidget().autoFocus(
                                        new AutoFocusCallback() {
                                            public void onAutoFocus(
                                                    boolean success,
                                                    Camera camera) {
                                                count = 1;
                                            }
                                        });
                            } catch (Exception e) {
                                e.printStackTrace();
                            }
                        }
                        AppGlobals.setIsFlashOn(true);
                        isLightOn = true;
                        NotifyFlashlight(context, isLightOn);

                    }
                }
            }

            Flashlight.turnMotorolaOn();
        }

    }


    private void flashOffApp() {
        Flashlight.getmCameraActivity().stopPreview();
        Flashlight.getmCameraActivity().release();
        Flashlight.setmCameraActivity(null);
        AppGlobals.setIsFlashOn(true);
        count = 0;

    }


    private void flashOffWidget() {
        FlashlightWidgetReceiver.getmCameraWidget().stopPreview();
        FlashlightWidgetReceiver.getmCameraWidget().release();
        FlashlightWidgetReceiver.setmCameraWidget(null);
        AppGlobals.setIsFlashOn(false);
        count = 0;

    }

    public static Camera getmCameraWidget() {
        return mCameraWidget;
    }

    public static void setmCameraWidget(Camera mCameraWidget) {
        FlashlightWidgetReceiver.mCameraWidget = mCameraWidget;
    }

    public static Parameters getParamsWidget() {
        return paramsWidget;
    }

    public static void setParamsWidget(Parameters paramsWidgetSet) {
        paramsWidget = paramsWidgetSet;
    }


    }
}

回答1:

Here is the whole code to run Falsh in background. all you need to put your code in a service. then start your service from your main activity.

Here is the service class:

public class ServiceFlash extends Service {
private boolean isFlashOn = false;
private Camera camera;
Context context ;
PackageManager pm;


@Override
public void onCreate() {
    // TODO Auto-generated method stub
    context = getApplicationContext();
    super.onCreate();

}
@Override
public int onStartCommand(Intent intent, int flags, int startId) {
    // TODO Auto-generated method stub
     pm = context.getPackageManager();

    if (!pm.hasSystemFeature(PackageManager.FEATURE_CAMERA)) {
        Log.e("err", "Device has no camera!");
        Toast.makeText(getApplicationContext(),
                "Your device doesn't have camera!", Toast.LENGTH_SHORT)
                .show();

        return 0;
    }

    camera = Camera.open();
    final Parameters p = camera.getParameters();

    // turn flash on
    if (isFlashOn) {
        Log.i("info", "torch is turned off!");
        p.setFlashMode(Parameters.FLASH_MODE_OFF);
        camera.setParameters(p);
        isFlashOn = false;
    } else {
        Log.i("info", "torch is turned on!");
        p.setFlashMode(Parameters.FLASH_MODE_TORCH);
        camera.setParameters(p);
        isFlashOn = true;
    }
    return super.onStartCommand(intent, flags, startId);

}

@Override
public IBinder onBind(Intent intent) {
    // TODO Auto-generated method stub
    return null;
}

Don't forget add this to your manifest:

<service
        android:name=".ServiceFlash"
        android:exported="false"/>

Your activity maybe like this: public class AppActivity extends Activity { private boolean isFlashOn = false; private Camera camera; private Button button;

@Override
protected void onStop() {
    super.onStop();

    if (camera != null) {
        camera.release();
    }
}

@Override
protected void onPause() {
    // TODO Auto-generated method stub
    super.onPause();

}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main);
    Intent front_translucent = new Intent(this, ServiceFlash.class);

    startService(front_translucent);
}

}

You can start your service from widget class like this (try to put this code inside onReceive method of widget class):

 // Create intent 
    Intent serviceIntent = new Intent(context, mService.class);
// start service 
context.startService(serviceIntent);

Enjoy..!

来源：https://stackoverflow.com/questions/25709391/flashlight-turns-off-when-other-apps-are-started-android