让ListView.ScrollIntoView滚动项到ListView中的中心（C＃） [英] Make ListView.ScrollIntoView Scroll the Item into the Center of the ListView (C#)

问题描述

ListView.ScrollIntoView（对象）目前发现的的ListView 并滚动到一个对象。如果被定位你正在滚动到对象的下方，它滚动对象顶端行。如果你的正上方，它滚动它进入视野在底部一行。

ListView.ScrollIntoView(object) currently finds an object in the ListView and scrolls to it. If you are positioned beneath the object you are scrolling to, it scrolls the object to the top row. If you are positioned above, it scrolls it into view at the bottom row.

我想有该项目滚动右转入我的列表视图的中心，如果它是当前不可见。有一个简单的方法来做到这一点？

I'd like to have the item be scrolled right into the center of my list view if it is currently not visible. Is there an easy way to accomplish this?

推荐答案

这是很容易的扩展方法我写了这样做的WPF。所有你需要做的一个项目滚动到视图的中心是调用一个方法。

It is very easy to do this in WPF with an extension method I wrote. All you have to do to scroll an item to the center of the view is to call a single method.

假设你有这样的XAML：

Suppose you have this XAML:

<ListView x:Name="view" ItemsSource="{Binding Data}" /> 
<ComboBox x:Name="box"  ItemsSource="{Binding Data}"
                        SelectionChanged="ScrollIntoView" /> 

您ScrollIntoView方法是简单：

Your ScrollIntoView method will be simply:

private void ScrollIntoView(object sender, SelectionChangedEventArgs e)
{
  view.ScrollToCenterOfView(box.SelectedItem);
} 

显然，这可以用一个视图模型以及而非明确引用的控制来完成。

Obviously this could be done using a ViewModel as well rather than referencing the controls explicitly.

以下是执行。这是很一般，处理所有的IScrollInfo可能性。它的工作原理与ListBox或任何其他的ItemsControl，并与包括StackPanel中，VirtualizingStackPanel，WrapPanel，DockPanel中，画布，网格等任何面板厂。

Following is the implementation. It is very general, handling all the IScrollInfo possibilities. It works with ListBox or any other ItemsControl, and works with any panel including StackPanel, VirtualizingStackPanel, WrapPanel, DockPanel, Canvas, Grid, etc.

只是把这个在cs文件的某处在您的项目：

Just put this in a .cs file somewhere in your project:

public static class ItemsControlExtensions
{
  public static void ScrollToCenterOfView(this ItemsControl itemsControl, object item)
  {
    // Scroll immediately if possible
    if(!itemsControl.TryScrollToCenterOfView(item))
    {
      // Otherwise wait until everything is loaded, then scroll
      if(itemsControl is ListBox) ((ListBox)itemsControl).ScrollIntoView(item);
      itemsControl.Dispatcher.BeginInvoke(DispatcherPriority.Loaded, new Action(() =>
        {
          itemsControl.TryScrollToCenterOfView(item);
        }));
    }
  }

  private static bool TryScrollToCenterOfView(this ItemsControl itemsControl, object item)
  {
    // Find the container
    var container = itemsControl.ItemContainerGenerator.ContainerFromItem(item) as UIElement;
    if(container==null) return false;

    // Find the ScrollContentPresenter
    ScrollContentPresenter presenter = null;
    for(Visual vis = container; vis!=null && vis!=itemsControl; vis = VisualTreeHelper.GetParent(vis) as Visual)
      if((presenter = vis as ScrollContentPresenter)!=null)
        break;
    if(presenter==null) return false;

    // Find the IScrollInfo
    var scrollInfo = 
        !presenter.CanContentScroll ? presenter :
        presenter.Content as IScrollInfo ??
        FirstVisualChild(presenter.Content as ItemsPresenter) as IScrollInfo ??
        presenter;

    // Compute the center point of the container relative to the scrollInfo
    Size size = container.RenderSize;
    Point center = container.TransformToAncestor((Visual)scrollInfo).Transform(new Point(size.Width/2, size.Height/2));
    center.Y += scrollInfo.VerticalOffset;
    center.X += scrollInfo.HorizontalOffset;

    // Adjust for logical scrolling
    if(scrollInfo is StackPanel || scrollInfo is VirtualizingStackPanel)
    {
      double logicalCenter = itemsControl.ItemContainerGenerator.IndexFromContainer(container) + 0.5;
      Orientation orientation = scrollInfo is StackPanel ? ((StackPanel)scrollInfo).Orientation : ((VirtualizingStackPanel)scrollInfo).Orientation;
      if(orientation==Orientation.Horizontal)
        center.X = logicalCenter;
      else
        center.Y = logicalCenter;
    }

    // Scroll the center of the container to the center of the viewport
    if(scrollInfo.CanVerticallyScroll) scrollInfo.SetVerticalOffset(CenteringOffset(center.Y, scrollInfo.ViewportHeight, scrollInfo.ExtentHeight));
    if(scrollInfo.CanHorizontallyScroll) scrollInfo.SetHorizontalOffset(CenteringOffset(center.X, scrollInfo.ViewportWidth, scrollInfo.ExtentWidth));
    return true;
  }

  private static double CenteringOffset(double center, double viewport, double extent)
  {
    return Math.Min(extent - viewport, Math.Max(0, center - viewport/2));
  }
  private static DependencyObject FirstVisualChild(Visual visual)
  {
    if(visual==null) return null;
    if(VisualTreeHelper.GetChildrenCount(visual)==0) return null;
    return VisualTreeHelper.GetChild(visual, 0);
  }
}

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