Java 安卓：取消后退按钮上的倒计时

当按下设备后退按钮时，如何停止倒计时（不是我制作的按钮，而是设备上的后退按钮）。这就是我尝试过的

@Override
public void onBackPressed() {
    flight_engineer.this.finish();
        win.cancel();
        win = null;
        Log.i("backPressed","hello");



}

此日志确实会打印hello，但当我成为新活动时，计时器（称为win）仍会计数

编辑：这是我如何使用计时器

   win = new CountDownTimer(120000,1000) {
        @Override
        public void onTick(long millisUntilFinished) {
            timer.setText("seconds remaining: " + millisUntilFinished / 1000);
        }

        @Override
        public void onFinish() {

           if(alti >= 28000 && alti <= 33000 && speed >= 280 && speed <= 320 && pressure >= 8 && pressure <= 12
                   && over_heat >= 700 && over_heat <= 750 && fuel > 50){

               Intent start = new Intent(flight_engineer.this, win.class);
               finish();
               flight_engineer.this.startActivity(start);

           }
            else
           {
               Intent start = new Intent(flight_engineer.this, losing.class);
               finish();
               flight_engineer.this.startActivity(start);

           }



        }
    };
    win.start();

---

计时器在哪里启动？这是您的活动吗？飞行工程师。这个。完成（）；调用win.cancel（）后调用finish（）；win=null；Log.i（“backPressed”、“hello”）；或者发布你的全部代码。我已经更新了代码

public class flight_engineer extends AppCompatActivity {

int fuel = 100;
int alti = 10000;
int speed = 100;
int over_heat = 600;
int pressure = 10;
boolean started = true;

CountDownTimer fuelCount;
CountDownTimer PSICount;
CountDownTimer speedTimer;
CountDownTimer spike;
CountDownTimer win;