wpf - Activate horizontal scrolling with mouse on ListView

Question

I've got a custom horizontal ListView with custom ScrollViewer inside it's template (created with Blend). I want it to scroll horizontally when using mouse scrolling wheel. How can I do that?

Answer 1

This should be done with a Behavior for greater reusability. Also, the logic from ZSH is redundant and could be simplified. Here's my code:

/// <summary>
/// Allows an <see cref="ItemsControl"/> to scroll horizontally by listening to the
/// <see cref="PreviewMouseWheel"/> event of its internal <see cref="ScrollViewer"/>.
/// </summary>
public class HorizontalScrollBehavior : Behavior<ItemsControl>
{
    /// <summary>
    /// A reference to the internal ScrollViewer.
    /// </summary>
    private ScrollViewer ScrollViewer { get; set; }

    /// <summary>
    /// By default, scrolling down on the wheel translates to right, and up to left.
    /// Set this to true to invert that translation.
    /// </summary>
    public bool IsInverted { get; set; }

    /// <summary>
    /// The ScrollViewer is not available in the visual tree until the control is loaded.
    /// </summary>
    protected override void OnAttached()
    {
        base.OnAttached();

        AssociatedObject.Loaded += OnLoaded;
    }

    private void OnLoaded(object sender, RoutedEventArgs e)
    {
        AssociatedObject.Loaded -= OnLoaded;

        ScrollViewer = VisualTreeHelpers.FindVisualChild<ScrollViewer>(AssociatedObject);

        if (ScrollViewer != null)
        {
            ScrollViewer.PreviewMouseWheel += OnPreviewMouseWheel;
        }
    }

    protected override void OnDetaching()
    {
        base.OnDetaching();

        if (ScrollViewer != null)
        {
            ScrollViewer.PreviewMouseWheel -= OnPreviewMouseWheel;
        }
    }

    private void OnPreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        var newOffset = IsInverted ?
            ScrollViewer.HorizontalOffset + e.Delta :
            ScrollViewer.HorizontalOffset - e.Delta;

        ScrollViewer.ScrollToHorizontalOffset(newOffset);
    }
}

You'll need to add the following references: System.Windows, System.Windows.Controls, System.Windows.Input, and you may need to get the Blend SDK NuGet package, and find and reference the System.Windows.Interactivity DLL in the Assemblies Extensions section.

Use this for VisualTreeHelpers:

public class VisualTreeHelpers
{
    /// <summary>
    /// Return the first visual child of element by type.
    /// </summary>
    /// <typeparam name="T">The type of the Child</typeparam>
    /// <param name="obj">The parent Element</param>
    public static T FindVisualChild<T>(DependencyObject obj) where T : DependencyObject
    {
        for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
        {
            DependencyObject child = VisualTreeHelper.GetChild(obj, i);
            if (child != null && child is T)
                return (T)child;
            else
            {
                T childOfChild = FindVisualChild<T>(child);
                if (childOfChild != null)
                    return childOfChild;
            }
        }
        return null;
     }
}

Reference: https://codereview.stackexchange.com/questions/44760/is-there-a-better-way-to-get-a-child

Note that it is NOT the same as VisualTreeHelper in Windows.System.Media.

Here's how to use it in XAML:

<ListBox>
    <i:Interaction.Behaviors>
        <behaviors:HorizontalScrollBehavior />
    </i:Interaction.Behaviors>
</ListBox>

Where the i namespace is declared as xmlns:i="http://schemas.microsoft.com/expression/2010/interactivity" and

behaviors is declared as

xmlns:behaviors="clr-namespace:MyNamespace"

where MyNamespace is the namespace that contains the HorizontalScrollBehavior class.