How to re-create Timer class object after canceling it?

Question

I'm making an Android app that turns on/off the flash light after a specified interval, by the user. It works well except when the Timer object is re-created after calling the .cancel() method for the second time, it crashes the app every time. Here's the initialization part:

Timer timer; //variable of Timer class
TimerTask timerTask; //variable of TimerTask class

And here's the method that is called when the button responsible to turn blinking on/off is pressed:

blink.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v){
            delay = Integer.valueOf(startDelay.getText().toString());
            gap = Integer.valueOf(blinkDelay.getText().toString());

            if(!isBlinking) { //isBlinking is a boolean to know whether to stop or re-start timer
                timer = new Timer(); //I'm creating an object of Timer class every time.
                isBlinking = true;
                timer.schedule(timerTask, delay, gap);

            }
            else{
                isBlinking = false;
                stoptimertask(); //this will cancel the 'timer' and make it null.
            }
        }
    });

The 'stoptimertask()' method from above code has:

public void stoptimertask() {
    //stop the timer, if it's not already null

    if (timer != null) {
        timer.cancel();
        timer = null;
    }

}

I'm setting the 'timertask' variable of TimerTask class from the method shown below. It is called in the onCreate() method of the main activity:

public void initializeTimerTask() {

    timerTask = new TimerTask() { //This is passed as the first argument to the timer.schedule() method
        public void run() {//Basically turns on/off flash. Works well.
            if(!state) {
                turnOnFlash();
                state = true;

            }
            else {
                turnOffFlash();
                state = false;
            }

        }
    };

My question is that why does the app crash when I press the blink button the third time?

When it is pressed for the first time, isBlinking is false, so the if block executes creating a new object of the Timer class and starting the timer.
When it is pressed for the second time, stoptimertask() is called which cancels the timer and sets timer variable to null.
When it is pressed again for the third time with different values for delay and gap, a new object of Timer class should be created, but the application crashes unexpectedly with a "Unfortunately the app has stopped" error. Where am I going wrong?

score 1 · Answer 1 · answered Mar 11 '16 at 16:28

1

You will have to purge as well.

timer.cancel();
timer.purge();

answered Mar 11 '16 at 16:28

vabhi vab

419
4
11

score 1 · Answer 2 · edited May 23 '17 at 11:50

1

Don't forget to purge after cancel.

Your code must be for stoptimertask() method.

public void stoptimertask() {
    //stop the timer, if it's not already null
    if (timer != null) {
        timer.cancel();
        timer.purge();
        timer = null;
    }
}

How to re-create Timer class object after canceling it?

2 Answers2