Question

ListView.ScrollIntoView(object)当前在ListView中找到一个对象并滚动到它。如果您位于要滚动的对象下方，则会将对象滚动到顶行。如果您位于上方，则会将其滚动到底行的视图中。

如果项目当前不可见，我想将项目滚动到列表视图的中心。有没有一种简单的方法可以实现这一目标？

Answer 1

使用我编写的扩展方法在WPF中执行此操作非常容易。将项目滚动到视图中心所需要做的就是调用单个方法。

假设你有这个XAML：

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

您的ScrollIntoView方法将简单：

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

显然，这也可以使用ViewModel来完成，而不是明确地引用控件。

以下是实施。它非常通用，处理所有IScrollInfo的可能性。它适用于ListBox或任何其他ItemsControl，适用于任何面板，包括StackPanel，VirtualizingStackPanel，WrapPanel，DockPanel，Canvas，Grid等。

将它放在项目中的某个.cs文件中：

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);
  }
}

Answer 2

Ray Burns上面的优秀答案是WPF特有的。

以下是适用于Silverlight的修改版本：

 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( 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 (UIElement vis = container; vis != null ; vis = VisualTreeHelper.GetParent(vis) as UIElement)
                if ((presenter = vis as ScrollContentPresenter) != null)
                    break;
            if (presenter == null) return false;

            // Find the IScrollInfo 
            var scrollInfo =
                !presenter.CanVerticallyScroll ? 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.TransformToVisual((UIElement)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(UIElement visual)
        {
            if (visual == null) return null;
            if (VisualTreeHelper.GetChildrenCount(visual) == 0) return null;
            return VisualTreeHelper.GetChild(visual, 0);
        }
    }

Answer 3

我似乎记得在某些时候自己做过这样的事情。就我的记忆而言，我所做的是：

确定对象是否已经可见。
如果它不可见，请获取所需对象的索引以及当前显示的对象数。
(index you want) - (number of objects displayed / 2)应该是最上面一行，所以请滚动到那个（当然，确保你不会消极）

Answer 4

如果你看一下Listbox的模板，它只是一个里面有itemspresenter的scrollviewer。您需要计算商品的尺寸，并使用滚动horizontally或vertically来定位滚动查看器中的商品。 april silverlight工具包有一个扩展方法GetScrollHost，您可以在列表框上调用它来获取底层的滚动查看器。

完成后，您可以使用当前的Horizontal或Vertical偏移量作为参照系，并按顺序移动列表。

Answer 5

下面的示例将找到listview的scrollviewer，并使用它将项目滚动到listview中间。

XAML：

<Window x:Class="ScrollIntoViewTest.Window1"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Height="300" Width="300">
    <Grid>
        <Grid.RowDefinitions>
            <RowDefinition Height="*" />
            <RowDefinition Height="Auto" />
        </Grid.RowDefinitions>
        <ListView Grid.Row="0" ItemsSource="{Binding Path=Data}" Loaded="OnListViewLoaded"/>
        <ComboBox Grid.Row="1" ItemsSource="{Binding Path=Data}" SelectionChanged="OnScrollIntoView" />
    </Grid>
</Window>

代码背后：

using System;
using System.Collections.Generic;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Media;

namespace ScrollIntoViewTest
{
    public partial class Window1 : Window
    {
        public Window1()
        {
            InitializeComponent();

            Data = new List<string>();
            for (int i = 0; i < 100; i++)
            {
                Data.Add(i.ToString());    
            }

            DataContext = this;
        }

        public List<string> Data { get; set; }

        private void OnListViewLoaded(object sender, RoutedEventArgs e)
        {
            // Assumes that the listview consists of a scrollviewer with a border around it
            // which is the default.
            Border border = VisualTreeHelper.GetChild(sender as DependencyObject, 0) as Border;
            _scrollViewer = VisualTreeHelper.GetChild(border, 0) as ScrollViewer;
        }

        private void OnScrollIntoView(object sender, SelectionChangedEventArgs e)
        {
            string item = (sender as ComboBox).SelectedItem as string;
            double index = Data.IndexOf(item) - Math.Truncate(_scrollViewer.ViewportHeight / 2);
            _scrollViewer.ScrollToVerticalOffset(index);
        }

        private ScrollViewer _scrollViewer;
    }
}

Answer 6

我找到了另一种方法来解决这个问题，假设我们中的一些人只需要根据项目模板找出视觉项目的高度，这将大大节省您的时间。

好的，我认为您的XAML的结构与此类似：

:
<Window.Resources>
   <DataTemplate x:Key="myTemplate">
      <UserControls1:myControl DataContext="{Binding}" />
   </DataTemplate>
</Window.Resources>
:
<ListBox Name="myListBox" ItemTemplate="{StaticResource ResourceKey=myTemplate}" />

你想要计算才能滚动到中心，但你不知道当前的高度是多少列表框中的每个项目..这是你可以找到的方法：

listBoxItemHeight = (double)((DataTemplate)FindResource("myTemplate")).LoadContent().GetValue(HeightProperty);

Answer 7

Ray Burns＆＃39;上面的优秀答案和Fyodor Soikin的评论：

＆＃34;实际上，它不能与任何其他ItemsControl一起使用... DataGrid 与虚拟化已打开无法合作。 ..＆＃34;

使用：

if (listBox.SelectedItem != null)
{
   listBox.ScrollIntoView(listBox.SelectedItem);
   listBox.ScrollToCenterOfView(listBox.SelectedItem);
}

@all：目前无法评论，需要50点声望

Make ListView.ScrollIntoView将Item滚动到ListView的中心（C＃）

7 个答案: