How to stop update value of slider while dragging it?

Question

I've slider that its value is bind to some property, and the property updates it all the time. While dragging the [thumb on] slider I want to stop this update value of slider from binding, until user finish it's dragging.

Is there any property on Slider to do that, or I need to write code for that?

Thanks in advance!

Answer 1

The template for Slider includes a Thumb, which raises the ThumbDragDelta event as the mouse is moved. Slider will always update the bound value immediately when it receives a ThumbDragDelta event.

The trick is to stop this event. The easiest way is to subclass Slider:

public class SliderIgnoreDelta : Slider
{
  protected override void OnThumbDragDelta(DragDeltaEventArgs e)
  {
    // Do nothing
  }
}

This slider will not update the value until the thumb drag completes.

Another solution is to intercept the ThumbDragDelta event on the Thumb. If you happen to be re-templating the Slider anyway, this might be a better solution. For example if you already have an EventBlocker class coded up that sets Handled true on the given RoutedEvent, you could put this in your template:

<Track.Thumb>
  <Thumb my:EventBlocker.EventToBlock="{x:Static Thumb.DragDeltaEvent}" />
</Track.Thumb>

But for most cases you'll probably want to go with my first solution.

Answer 2

Hi this solution works for me. Just override Slider class and bind to FinalValue in xaml.

public class ExSlider : Slider
{
    public double FinalValue
    {
        get { return (double)GetValue(FinalValueProperty); }
        set { SetValue(FinalValueProperty, value); }
    }

    public static readonly DependencyProperty FinalValueProperty =
        DependencyProperty.Register(
            "FinalValue", typeof(double), typeof(ExSlider),
            new FrameworkPropertyMetadata(0d,
                FrameworkPropertyMetadataOptions.BindsTwoWayByDefault));

    protected override void OnThumbDragCompleted(DragCompletedEventArgs e)
    {
        base.OnThumbDragCompleted(e);
        FinalValue = Value;
    }

}

Answer 3

I had the same issue so I made a simple slider extension as the next best thing. Adds two events to the slider:

ThumbDragStarted ThumbDragCompleted

public class SliderWithDraggingEvents : Slider
{
    public delegate void ThumbDragStartedHandler(object sender, DragStartedEventArgs e);
    public event ThumbDragStartedHandler ThumbDragStarted;


    public delegate void ThumbDragCompletedHandler(object sender, DragCompletedEventArgs e);
    public event ThumbDragCompletedHandler ThumbDragCompleted;

    protected override void OnThumbDragStarted(DragStartedEventArgs e)
    {
        if (ThumbDragStarted != null) ThumbDragStarted(this, e);
        base.OnThumbDragStarted(e);
    }

    protected override void OnThumbDragCompleted(DragCompletedEventArgs e)
    {
        if (ThumbDragCompleted != null) ThumbDragCompleted(this, e);
        base.OnThumbDragCompleted(e);
    }
}

Answer 4

Added a flag to indicate dragging and only send out value changed events when the slider is being dragged.

 public class CustomSlider:Slider
{

    public bool IsDragging { get; protected set; }
    protected override void OnThumbDragCompleted(System.Windows.Controls.Primitives.DragCompletedEventArgs e)
    {
        IsDragging = false;
        base.OnThumbDragCompleted(e);

    }

    protected override void OnThumbDragStarted(System.Windows.Controls.Primitives.DragStartedEventArgs e)
    {
        IsDragging = true;
        base.OnThumbDragStarted(e);
    }

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