WPF覆盖列表框中的ScrollVIewer

Question

I made a class named "AniScrollViewer," it can set the vertical scroll offset
to animate Scrollviewer code-behind.

public class AniScrollViewer : ScrollViewer {
    public static readonly DependencyProperty CurrentVerticalOffsetProperty =
        DependencyProperty.Register("CurrentVerticalOffset", typeof(double), typeof(AniScrollViewer),
        new PropertyMetadata(new PropertyChangedCallback(OnVerticalChanged)));

    public double CurrentVerticalOffset {
        get { return (double)GetValue(CurrentVerticalOffsetProperty); }
        set { SetValue(CurrentVerticalOffsetProperty, value); }
    }

    private static void OnVerticalChanged(DependencyObject property, DependencyPropertyChangedEventArgs e) {
        AniScrollViewer viewer = property as AniScrollViewer;
        viewer.ScrollToVerticalOffset((double)e.NewValue);
    }
}

I want to push this 'AniScrollViewer' into a Listbox

I meet couple of problems:

• The Listbox class already has 'scrollviewer' inside. I want to replace
  the default listbox scrollviewer with my custom AniScrollViewer, but I don't know how to do this.
• I want to get ScrollViewer in Listbox code-behind. Like this:
  

Listbox listbox (this is already definded in XAML)
AniScrollViewer scrollviewer = listbox.~~~~;

Please help.

Answer 1

• To replace the default ScrollViewer with a custom one, Define a custom Style for the ListBox and in the ControlTemplate switch out the default ScrollViewer with your one( local:AniScrollViewer ). Now any ListBox using this Style will have your ScrollViewer . Default ControlTemplate and Style can be found Here
• To get the ScrollViewer in the code-behind, you can use this as a reference. In the function

GetScrollViewer(DependencyObject o)

check it to be type safe with your custom ScrollViewer such as

if (o is AniScrollViewer)
  return o;

Alternate

However in your case, am not sure why your opting to subclass the ScrollViewer for this. Instead of the hassle of this with defining your own ListBox ControlTemplate , maybe try using an attached property. Something like:

public class ScrollAnimator {
  public static readonly DependencyProperty ScrollToProperty =
    DependencyProperty.RegisterAttached(
      "ScrollTo",
      typeof(double),
      typeof(ScrollAnimator),
      new FrameworkPropertyMetadata(0.0, FrameworkPropertyMetadataOptions.None, ScrollToChangedCallback));

  private static void ScrollToChangedCallback(
    DependencyObject dependencyObject, DependencyPropertyChangedEventArgs dependencyPropertyChangedEventArgs) {
    ScrollViewer viewer = GetScrollViewer(dependencyObject) as ScrollViewer;
    if (viewer != null)
      viewer.ScrollToVerticalOffset((double)dependencyPropertyChangedEventArgs.NewValue);

    // Modify Above code to however you want to do the animation.
  }

  public static DependencyObject GetScrollViewer(DependencyObject o) {
    if (o is ScrollViewer)
      return o;

    for (int i = 0; i < VisualTreeHelper.GetChildrenCount(o); i++) {
      var child = VisualTreeHelper.GetChild(o, i);
      var result = GetScrollViewer(child);
      if (result == null)
        continue;
      return result;
    }
    return null;
  }

  public static void SetScrollTo(UIElement element, Orientation value) {
    element.SetValue(ScrollToProperty, value);
  }

  public static Orientation GetScrollTo(UIElement element) {
    return (Orientation)element.GetValue(ScrollToProperty);
  }
}

and usage:

<ListBox ItemsSource="{Binding Items}"
         local:ScrollAnimator.ScrollTo="{Binding ScrollTo}" />

This way you don't have the need to define custom ControlTemplate 's and all the overhead that come with it.