double tap for zoom is not working..

i take one scrollview inside that i take an imageview and add gesture recognizer and attach to it but the problem is when i double tap on image it's not working...how to solve this here is my code..

var tapGestureRecognizer = new TapGestureRecognizer(){NumberOfTapsRequired=2};
        tapGestureRecognizer.Tapped += (sender, e) => {
            scrollView.Scale=2;
        };
        image.GestureRecognizers.Add(tapGestureRecognizer);