ScrollViewer 上 VerticalOffset 属性的双向绑定？

Question

我在 Silverlight 3.0 中有一个视图和一个视图模型。

该视图包含一个标准的 ScrollViewer，它包含动态内容。

根据 ScrollViewer 中的内容，用户可能已经滚动到内容的一半，然后执行导致 ScrollViewer 加载新内容的操作，但 ScrollViewer 不会自动滚动到顶部。

我希望能够绑定到 VerticalOffset 属性，但它是只读的。 关于可附加行为的任何想法？ 有任何想法吗？

谢谢。

Answer 1

以下博客文章提供了一个附加行为，该行为公开了滚动查看器的垂直/水平偏移，以便您可以绑定到它们，或在代码中设置它们：

http://blog.scottlogic.com/2010/07/21/exposing-and-binding-to-a-silverlight-scrollviewers-scrollbars.html

这允许以下标记：

<ScrollViewer 
    local:ScrollViewerBinding.VerticalOffset="{Binding YPosition, Mode=TwoWay}"
    local:ScrollViewerBinding.HorizontalOffset="{Binding XPosition, Mode=TwoWay}">
    <!-- Big content goes here! -->
</ScrollViewer>

Answer 2

由于您使用的是 ViewModel，我认为“导致 ScrollViewer 加载新内容的操作”是内部或对 ViewModel 所做更改的结果。 在这种情况下，我会向 ViewModel 添加一个事件，每次发生此类更改时都会触发该事件。

您的视图可以在此事件上添加处理程序，并在触发时在 ScrollViewer 上调用 ScrollToVerticalPosition。

Answer 3

我已经简化了@ColinE 的解决方案。 我没有挂钩到ScrollBar.ValueChanged事件，而是挂钩到ScrollViewer.ScrollChanged事件。 所以，1. 没有必要在可视化树中找到ScrollBar和 2. ScrollBar.ValueChanged当ScrollViewer的内容发生变化并且我不想捕捉这些状态时，会在某些过渡状态中调用。

我发布了VerticalOffset代码， HorizontalOffset是类似的：

/// <summary>
/// VerticalOffset attached property
/// </summary>
public static readonly DependencyProperty VerticalOffsetProperty =
    DependencyProperty.RegisterAttached("VerticalOffset", typeof(double),
    typeof(ScrollViewerBinding), new FrameworkPropertyMetadata(double.NaN,
        FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
        OnVerticalOffsetPropertyChanged));

/// <summary>
/// Just a flag that the binding has been applied.
/// </summary>
private static readonly DependencyProperty VerticalScrollBindingProperty =
    DependencyProperty.RegisterAttached("VerticalScrollBinding", typeof(bool?), typeof(ScrollViewerBinding));

public static double GetVerticalOffset(DependencyObject depObj)
{
    return (double)depObj.GetValue(VerticalOffsetProperty);
}

public static void SetVerticalOffset(DependencyObject depObj, double value)
{
    depObj.SetValue(VerticalOffsetProperty, value);
}

private static void OnVerticalOffsetPropertyChanged(DependencyObject d,
    DependencyPropertyChangedEventArgs e)
{
    ScrollViewer scrollViewer = d as ScrollViewer;
    if (scrollViewer == null)
        return;

    BindVerticalOffset(scrollViewer);
    scrollViewer.ScrollToVerticalOffset((double)e.NewValue);
}

public static void BindVerticalOffset(ScrollViewer scrollViewer)
{
    if (scrollViewer.GetValue(VerticalScrollBindingProperty) != null)
        return;

    scrollViewer.SetValue(VerticalScrollBindingProperty, true);
    scrollViewer.ScrollChanged += (s, se) =>
    {
        if (se.VerticalChange == 0)
            return;
        SetVerticalOffset(scrollViewer, se.VerticalOffset);
    };
}

并在 XAML 中使用它：

<ScrollViewer local:ScrollViewerBinding.VerticalOffset="{Binding ScrollVertical}">
    <!-- content ... -->
</ScrollViewer>

Answer 4

我从这个开始，但注意到没有清理阶段，所以这里是水平和垂直偏移可绑定的完整实现：

using System.Windows;
using System.Windows.Controls;

namespace Test
{
    public static class ScrollPositionBehavior
    {
        public static readonly DependencyProperty HorizontalOffsetProperty =
            DependencyProperty.RegisterAttached(
                "HorizontalOffset",
                typeof(double),
                typeof(ScrollPositionBehavior),
                new FrameworkPropertyMetadata(
                    double.NaN,
                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                    OnHorizontalOffsetPropertyChanged));

        public static readonly DependencyProperty VerticalOffsetProperty =
            DependencyProperty.RegisterAttached(
                "VerticalOffset",
                typeof(double),
                typeof(ScrollPositionBehavior),
                new FrameworkPropertyMetadata(
                    double.NaN,
                    FrameworkPropertyMetadataOptions.BindsTwoWayByDefault,
                    OnVerticalOffsetPropertyChanged));

        private static readonly DependencyProperty IsScrollPositionBoundProperty =
            DependencyProperty.RegisterAttached("IsScrollPositionBound", typeof(bool?), typeof(ScrollPositionBehavior));

        public static void BindOffset(ScrollViewer scrollViewer)
        {
            if (scrollViewer.GetValue(IsScrollPositionBoundProperty) is true)
                return;

            scrollViewer.SetValue(IsScrollPositionBoundProperty, true);

            scrollViewer.Loaded += ScrollViewer_Loaded;
            scrollViewer.Unloaded += ScrollViewer_Unloaded;
        }

        public static double GetHorizontalOffset(DependencyObject depObj)
        {
            return (double)depObj.GetValue(HorizontalOffsetProperty);
        }

        public static double GetVerticalOffset(DependencyObject depObj)
        {
            return (double)depObj.GetValue(VerticalOffsetProperty);
        }

        public static void SetHorizontalOffset(DependencyObject depObj, double value)
        {
            depObj.SetValue(HorizontalOffsetProperty, value);
        }

        public static void SetVerticalOffset(DependencyObject depObj, double value)
        {
            depObj.SetValue(VerticalOffsetProperty, value);
        }

        private static void OnHorizontalOffsetPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ScrollViewer scrollViewer = d as ScrollViewer;
            if (scrollViewer == null || double.IsNaN((double)e.NewValue))
                return;

            BindOffset(scrollViewer);
            scrollViewer.ScrollToHorizontalOffset((double)e.NewValue);
        }

        private static void OnVerticalOffsetPropertyChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            ScrollViewer scrollViewer = d as ScrollViewer;
            if (scrollViewer == null || double.IsNaN((double)e.NewValue))
                return;

            BindOffset(scrollViewer);
            scrollViewer.ScrollToVerticalOffset((double)e.NewValue);
        }

        private static void ScrollChanged(object s, ScrollChangedEventArgs se)
        {
            if (se.VerticalChange != 0)
                SetVerticalOffset(s as ScrollViewer, se.VerticalOffset);

            if (se.HorizontalChange != 0)
                SetHorizontalOffset(s as ScrollViewer, se.HorizontalOffset);
        }

        private static void ScrollViewer_Loaded(object sender, RoutedEventArgs e)
        {
            var scrollViewer = sender as ScrollViewer;
            scrollViewer.ScrollChanged += ScrollChanged;
        }

        private static void ScrollViewer_Unloaded(object sender, RoutedEventArgs e)
        {
            var scrollViewer = sender as ScrollViewer;
            scrollViewer.SetValue(IsScrollPositionBoundProperty, false);

            scrollViewer.ScrollChanged -= ScrollChanged;
            scrollViewer.Loaded -= ScrollViewer_Loaded;
            scrollViewer.Unloaded -= ScrollViewer_Unloaded;
        }
    }
}