Keep app running in background on Android

Question

I am really new to Android Programming. I am working on a simple app: FlashLight for Android.

I need the app to continue run in background if the user presses the menubutton or locks the screen. The light should not stop until the user presses the button the stop the light.

Below is my code:

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.pm.PackageManager;
import android.hardware.Camera;
import android.hardware.Camera.Parameters;
import android.media.MediaPlayer;
import android.media.MediaPlayer.OnCompletionListener;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.ImageButton;

public class MainActivity
        extends Activity {
    ImageButton btnSwitch;
    private Camera camera;
    private boolean isFlashOn;
    private boolean hasFlash;
    Parameters params;
    MediaPlayer mp;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        // flash switch button
        btnSwitch = (ImageButton) findViewById(R.id.btnSwitch);
        // First check if device is supporting flashlight or not
        hasFlash = getApplicationContext().getPackageManager().hasSystemFeature(PackageManager.FEATURE_CAMERA_FLASH);
        if(!hasFlash) {
            // device doesn't support flash
            // Show alert message and close the application
            AlertDialog alert = new AlertDialog.Builder(MainActivity.this).create();
            alert.setTitle("Error");
            alert.setMessage("Sorry, your device doesn't support flash light!");
            alert.setButton("OK", new DialogInterface.OnClickListener() {
                public void onClick(DialogInterface dialog, int which) {
                    // closing the application
                    finish();
                }
            });
            alert.show();
            return;
        }
        // get the camera
        getCamera();
        // displaying button image
        toggleButtonImage();
        // Switch button click event to toggle flash on/off
        btnSwitch.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if(isFlashOn) {
                    // turn off flash
                    turnOffFlash();
                } else {
                    // turn on flash
                    turnOnFlash();
                }
            }
        });
    }

    // Get the camera
    private void getCamera() {
        if(camera == null) {
            try {
                camera = Camera.open();
                params = camera.getParameters();
            } catch(RuntimeException e) {
                Log.e("Camera Error. Failed to Open. Error: ", e.getMessage());
            }
        }
    }

    // Turning On flash
    private void turnOnFlash() {
        if(!isFlashOn) {
            if(camera == null || params == null) {
                return;
            }
            params = camera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_TORCH);
            camera.setParameters(params);
            camera.startPreview();
            isFlashOn = true;
            // changing button/switch image
            toggleButtonImage();
        }
    }

    // Turning Off flash
    private void turnOffFlash() {
        if(isFlashOn) {
            if(camera == null || params == null) {
                return;
            }
            params = camera.getParameters();
            params.setFlashMode(Parameters.FLASH_MODE_OFF);
            camera.setParameters(params);
            camera.stopPreview();
            isFlashOn = false;
            // changing button/switch image
            toggleButtonImage();
        }
    }

    /*
     * Toggle switch button images
     * changing image states to on / off
     * */
    private void toggleButtonImage() {
        if(isFlashOn) {
            btnSwitch.setImageResource(R.drawable.btn_switch_on);
        } else {
            btnSwitch.setImageResource(R.drawable.btn_switch_off);
        }
    }

    /*
 * Playing sound
 * will play button toggle sound on flash on / off
 * */
    private void playSound() {
        if(isFlashOn) {
            mp = MediaPlayer.create(MainActivity.this, R.raw.light_switch_off);
        } else {
            mp = MediaPlayer.create(MainActivity.this, R.raw.light_switch_on);
        }
        mp.setOnCompletionListener(new OnCompletionListener() {
            @Override
            public void onCompletion(MediaPlayer mp) {
                // TODO Auto-generated method stub
                mp.release();
            }
        });
        mp.start();
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();
    }

    @Override
    protected void onPause() {
        super.onPause();
        // on pause turn off the flash
        turnOffFlash();
    }

    @Override
    protected void onRestart() {
        super.onRestart();
    }

    @Override
    protected void onResume() {
        super.onResume();
        // on resume turn on the flash
        if(hasFlash) {
            turnOnFlash();
        }
    }

    @Override
    protected void onStart() {
        super.onStart();
        // on starting the app get the camera params
        getCamera();
    }

    @Override
    protected void onStop() {
        super.onStop();
        // on stop release the camera
        if(camera != null) {
            camera.release();
            camera = null;
        }
    }
}

Answer 1

You;re turning off the light in onPause. When the screen is locked or the app is minimized, onPause is called. If you don't want that to happen, don't call it there.

Answer 2

I think you are searching for Services: http://developer.android.com/guide/components/services.html

They are very similar to an Activity but do dot provide a user interface and can run in the background.