Question

I’m creating an app for make the flash camera blink, but I have a problem with switching off the method. These are my variables:

Camera camera = null;
Parameters parameters;
int delay = 600;
int period = 600;
int delay1 = 300;
int period1 = 600;
Timer timer, timer2;

This method I’m using to make the flash camera blink:

timer = new Timer();
    timer.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            cameraOn();
            }
    },delay1,period1);

    timer2 = new Timer();
    timer2.scheduleAtFixedRate(new TimerTask() {
        @Override
        public void run() {
            cameraOff();
            }
    },delay,period);

And now is when the problem comes, there’s a button to switch off all this, but sometimes it works and sometimes it doesn’t. Sometimes it switches off perfect, sometimes it goes back to the previous activity like I want, but the flash camera stays switched on. What is wrong? Here are the methods to switch on-off the camera flash:

private void cameraOff() {
     parameters.setFlashMode(Parameters.FLASH_MODE_OFF);
     camera.setParameters(parameters);
     camera.release();
     camera = null;
}

private void cameraOn() {
     camera = Camera.open();
     parameters = camera.getParameters();
     parameters.setFlashMode(Parameters.FLASH_MODE_TORCH);
     camera.setParameters(parameters);
}

And here is the button:

@Override
public void onClick(View arg0) {
    timer.cancel();
    timer2.cancel();
    if(camera != null){
        cameraOff();
    }else{
        finish();
    }
}

Answer 1

Your application (as provided) is never going to work, due to a design flaw:

In the cameraOff() method you set camera to null. This method is triggered at a fixed interval, so next time the method is called again you have a NullPointerException as camera was set to null…

I do not know why you feel the urge to set it to null, but you need to do so elsewhere, or add checks whether camera is null or not.

Furthermore (to probable cause of your problem), the TimerTasks are executed on a different thread. When you cancel your timers, the value of camera is unknown and it might be possible that cameraOff() is called twice. Once from the TimerTask thread (as it was about to execute) and once from your main thread (because camera was not yet set so null).

Again, I wonder why you need to set camera to null, as this seems to cause most of your problems.