ValueChanged event not working on click Xamarin forms

when Click on Slider then ValueChanged event is not getting trigger, but when I slide then this event is trigger

bellow is code

void OnSliderValueChanged(object sender, ValueChangedEventArgs e)
{
var newStep = Math.Round(e.NewValue / 0.5);
var a = (Slider)sender;
a.Value = newStep * 0.5;
}

The Slider is in ListView

Thanks,