How to change a Slider's Value with the mouse wheel?

Question

I want to change the value of a Slider to the mouse wheel: When I scroll up, the Slider's Value property should increase and when I scroll down, it should decrease.
The behavior should be independent of the mouse position or the current focus.

Preferably the solution uses binding and is XAML only but a code-behind solution would suffice as well.

Answer 1

You could use an attached behaviour that hooks up the PreviewMouseWheel event of the parent Window and sets the value of the Slider.

Using an attached behaviour enables you to encapsulate the functionality and reuse it for any Slider control without having to modify the code-behind file of each view.

Here is an example for your reference.

public class MouseWheelBehavior
{
    public static double GetValue(Slider slider)
    {
        return (double)slider.GetValue(ValueProperty);
    }

    public static void SetValue(Slider slider, double value)
    {
        slider.SetValue(ValueProperty, value);
    }

    public static readonly DependencyProperty ValueProperty =
        DependencyProperty.RegisterAttached(
        "Value",
        typeof(double),
        typeof(MouseWheelBehavior),
        new UIPropertyMetadata(0.0, OnValueChanged));

    public static Slider GetSlider(UIElement parentElement)
    {
        return (Slider)parentElement.GetValue(SliderProperty);
    }

    public static void SetSlider(UIElement parentElement, Slider value)
    {
        parentElement.SetValue(SliderProperty, value);
    }

    public static readonly DependencyProperty SliderProperty =
        DependencyProperty.RegisterAttached(
        "Slider",
        typeof(Slider),
        typeof(MouseWheelBehavior));


    private static void OnValueChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
    {
        Slider slider = d as Slider;
        slider.Loaded += (ss, ee) =>
        {
            Window window = Window.GetWindow(slider);
            if (window != null)
            {
                SetSlider(window, slider);
                window.PreviewMouseWheel += Window_PreviewMouseWheel;
            }
        };
        slider.Unloaded += (ss, ee) => 
        {
            Window window = Window.GetWindow(slider);
            if(window != null)
            {
                SetSlider(window, null);
                window.PreviewMouseWheel -= Window_PreviewMouseWheel;
            }
        };
    }

    private static void Window_PreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        Window window = sender as Window;
        Slider slider = GetSlider(window);
        double value = GetValue(slider);
        if(slider != null && value != 0)
        {
            slider.Value += slider.SmallChange * e.Delta / value;
        }
    }
}

Usage:

<Slider local:MouseWheelBehavior.Value="120" />