How can I detect when the XAML Slider is Completed?

Question

In XAML I have the <Slider />. It has the ValueChanged event. This event fires with every change to Value. I need to detect when the value change is over. LostFocus, PointerReleased are not the correct event. How can I detect this?

Answer 1

You can create a new class and inherit from Slider. From there on, you can look for the Thumb control & listen for the events you want.

Something like this should work:

public class SliderValueChangeCompletedEventArgs : RoutedEventArgs
{
    private readonly double _value;

    public double Value { get { return _value; } }

    public SliderValueChangeCompletedEventArgs(double value)
    {
        _value = value;
    }
}
public delegate void SlideValueChangeCompletedEventHandler(object sender, SliderValueChangeCompletedEventArgs args);

public class ExtendedSlider : Slider
{
    public event SlideValueChangeCompletedEventHandler ValueChangeCompleted;
    private bool _dragging = false;

    protected void OnValueChangeCompleted(double value)
    {
        if (ValueChangeCompleted != null)
        {
            ValueChangeCompleted(this, new SliderValueChangeCompletedEventArgs(value) );
        }
    }

    protected override void OnApplyTemplate()
    {
        base.OnApplyTemplate();
        var thumb = base.GetTemplateChild("HorizontalThumb") as Thumb;
        if (thumb != null)
        {
            thumb.DragStarted += ThumbOnDragStarted;
            thumb.DragCompleted += ThumbOnDragCompleted;
        }
        thumb = base.GetTemplateChild("VerticalThumb") as Thumb;
        if (thumb != null)
        {
            thumb.DragStarted += ThumbOnDragStarted;
            thumb.DragCompleted += ThumbOnDragCompleted;
        }
    }

    private void ThumbOnDragCompleted(object sender, DragCompletedEventArgs e)
    {
        _dragging = false;
        OnValueChangeCompleted(this.Value);
    }

    private void ThumbOnDragStarted(object sender, DragStartedEventArgs e)
    {
        _dragging = true;
    }

    protected override void OnValueChanged(double oldValue, double newValue)
    {
        base.OnValueChanged(oldValue, newValue);
        if (!_dragging)
        {
            OnValueChangeCompleted(newValue);
        }
    }
}