我在 Silverlight 3.0 中有一个 View 和一个 ViewModel。
视图包含一个标准的 ScrollViewer，其中包含动态内容。
根据 ScrollViewer 中的内容，用户可能已经向下滚动了一半内容，然后执行了导致 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？ 有什么想法吗？
谢谢。
【问题讨论】：
标签： c# silverlight xaml
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/水平偏移量，以便您可以绑定到它们，或在代码中设置它们：
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>
【讨论】：
scrollViewer.ScrollChanged，不需要找ScrollBar。
由于您使用的是 ViewModel，我认为“导致 ScrollViewer 加载新内容的操作”是在 ViewModel 内部或对 ViewModel 进行更改的结果。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一个处理程序，并在其触发时在 ScrollViewer 上调用 ScrollToVerticalPosition。
【讨论】：
我已经简化了@ColinE 的解决方案。我没有挂钩ScrollBar.ValueChanged 事件，而是挂钩ScrollViewer.ScrollChanged 事件。因此，1. 没有必要在可视化树中找到 ScrollBar 和 2. ScrollBar.ValueChanged 在 ScrollViewer 的内容发生变化时在某些转换状态中被调用，我不想捕捉这些状态。
我发布了VerticalOffset 的代码，HorizontalOffset 类似：
/// <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>
【讨论】：
我从这个开始，但注意到没有清理阶段，所以这里是完整的实现，水平和垂直偏移均可绑定：
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;
}
}
}
【讨论】：
if (d is not ScrollViewer scrollViewer || double.IsNaN((double)e.NewValue))