按住主页按钮时如何保持手电筒开启？

Question

我正在开发一个非常简单的手电筒应用程序，虽然我已经成功实现了我想要的东西，但我希望以我想要的方式执行它。目前我的手电筒在我的活动处于活动状态时保持打开状态，只要我按下主页按钮以最小化手电筒关闭的活动。我希望手电筒只有在我的活动中点击关闭按钮时才会保持开启和关闭状态。

public class FlashLightActivity 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);
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    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(FlashLightActivity.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;
        }
        // play sound
        playSound();

        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;
        }
        // play sound
        playSound();

        params = camera.getParameters();
        params.setFlashMode(Parameters.FLASH_MODE_OFF);
        camera.setParameters(params);
        camera.stopPreview();
        isFlashOn = false;

        // changing button/switch image
        toggleButtonImage();
    }
}

/*
 * Playing sound
 * will play button toggle sound on flash on / off
 * */
private void playSound(){
    if(isFlashOn){
        mp = MediaPlayer.create(FlashLightActivity.this, R.raw.light_switch_off);
    }else{
        mp = MediaPlayer.create(FlashLightActivity.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();
}

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

@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;
    }
}
}