You need to use
CountDownTimer.cancel();
as soon as you want the timer to stop incrementing or decrementing.
http://developer.android.com/reference/android/os/CountDownTimer.html#cancel%28%29
Also, I would recomment that you make your CountDownTimer a member variable, so that you can cancel it from anywhere:
public class QuestionActivity extends Activity implements OnClickListener {
private CountDownTimer counterTimer;
// ...
public void setTimer() {
final long finishTime = 15;
counterTimer = new CountDownTimer(finishTime * 1000, 1000) {
public void onFinish() {
currentGame.decrementScore();
setQuestions();
}
public void onTick(long millisUntilFinished) {
TextView time = (TextView) findViewById(R.id.timers);
time.setText( " "+millisUntilFinished/1000);
}
};
counterTimer.start();
}
}