Android CountDownTimer如何取消

Question

无法取消CountDownTimer。 我引用此链接CountDownTimer

CountDownTimer mtimer  = new CountDownTimer(30000, 1000) {
    public void onTick(long millisUntilFinished) {
        Toast.makeText(getApplicationContext(), "seconds remaining: " + millisUntilFinished / 1000, Toast.LENGTH_SHORT).show();
        Log.e("seconds remaining:", String.valueOf(millisUntilFinished / 1000));
    }

    public void onFinish() {
        Toast.makeText(getApplicationContext(), "Done!", Toast.LENGTH_SHORT).show();
        Log.e("Finish called "," GG");
        // Trigger();
    }
};

我打电话给mtimer.start（）;但无法取消mtimer.cancel（）;

GeofenceBroadcastReceiver.java

public class GeofenceBroadcastReceiver extends BroadcastReceiver {
CountDownTimer mtimer = null;
public int GEOFENCE_RADIUS ; // in meters
public int MINUTE;
public int GEOFENCE_DURATION ;


@Override
public void onReceive(Context context, Intent intent) {
    SharedPreferences localShared = PreferenceManager.getDefaultSharedPreferences(getApplicationContext());
    GEOFENCE_RADIUS = localShared.getInt("SelectedRadius", -1);
    GEOFENCE_DURATION= localShared.getInt("SelectedDuration",-1);
    Log.e("RECIEVER GEO DURATION", String.valueOf(GEOFENCE_DURATION));

    GeofencingEvent event = GeofencingEvent.fromIntent(intent);
    String transition = mapTransition(event.getGeofenceTransition());
    Log.e("transition",transition);
    Log.e("getGeofenceTransition", String.valueOf(event.getGeofenceTransition()));


    NotificationManager nm = (NotificationManager) context.getSystemService(Context.NOTIFICATION_SERVICE);
    Notification notification = new NotificationCompat.Builder(context)
            .setVibrate(new long[] { 1000, 1000, 500,500 })
            .setSmallIcon(R.drawable.start)
            .setContentTitle("Geofence Notification!")
            .setDefaults(Notification.DEFAULT_LIGHTS | Notification.DEFAULT_VIBRATE | Notification.DEFAULT_SOUND)
            .setContentText(transition)
            .setTicker("Geofence action")
            .build();
    nm.notify(0, notification);

}

public String mapTransition( int event) {
        MINUTE = (GEOFENCE_DURATION * 60 * 1000);
    Log.e("MINUTE", String.valueOf(MINUTE));
     mtimer  = new CountDownTimer(MINUTE, 1000) {
        public void onTick(long millisUntilFinished) {
            Toast.makeText(getApplicationContext(), "seconds remaining: " + millisUntilFinished / 1000, Toast.LENGTH_SHORT).show();
            Log.e("seconds remaining:", String.valueOf(millisUntilFinished / 1000));

        }
        public void onFinish() {
            Toast.makeText(getApplicationContext(), "Done!", Toast.LENGTH_SHORT).show();
            Log.e("Finish called "," GG");
            Trigger();
        }

    };

    switch (event) {
        case Geofence.GEOFENCE_TRANSITION_ENTER:{
            mtimer.start();

        }
        return "ENTER";
        case Geofence.GEOFENCE_TRANSITION_EXIT:{
            mtimer.cancel();

        }
         return "EXIT";
        default:
            return "UNKNOWN";
    }
}

在switch case语句中，我可以在检测到ENTER时启动Timer，但是我无法取消Timer。