Silverlight 3 – ListBox:如何实现Smooth Scroll并捕获MouseDown / MouseUp事件

我正在尝试根据我的需要调整ListBox的行为,我遇到了几个问题

1)如何以编程方式设置ListBox的滚动位置
ListBox不提供其内部ScrollViewer的访问器,因此您无法将其滚动到任何您想要的位置.

2)如何准确设置垂直滚动(即如何平滑滚动)?
默认情况下,无法通过一次滚动一个完整元素来滚动其他列表(列表框将始终确保第一个元素完全显示)

在大多数情况下这种行为是可以的,但不是我的:我想要一个平稳的运动…),

WPF有这个问题的解决方案,但Silverlight没有(见问题“is-it-possible-to-implement-smooth-scroll-in-a-wpf-listview”).

3)如何捕获MouseDown和MouseUp事件:
如果您继承ListBox,则可能能够捕获MouseUp和MouseMove事件.但是,MouseUp事件永远不会被触发(我怀疑它被ListBox子元素吃掉了)

我找到了答案,所以我会自己回答.

1)如何使ListBox平滑滚动:
这个问题在SilverLight 2中没有发生,它只发生在SilverLight 3中,其中引入了VirtualizedStackPanel.
VirtualizedStackPanel可以在巨大的列表中实现更快的刷新(因为只绘制了可见元素)

有一个解决方法(请注意,它不应该在大型列表中使用):重新定义ListBox的ItemPanelTemplate,以便它使用StackPanel:

<navigation:Page.Resources>
    <ItemsPanelTemplate x:Key="ItemsPanelTemplate">
        <StackPanel/>
    </ItemsPanelTemplate>
</navigation:Page.Resources>

<StackPanel Orientation="Vertical"  x:Name="LayoutRoot">                       
        <ListBox x:Name="list" ItemsPanel="{StaticResource ItemsPanelTemplate}">
        </ListBox>
</StackPanel>

2)如何以编程方式更改滚动位置
请参阅下面的ListBox的子类:它提供了ListBox的内部ScrollViewer的访问器

3)如何捕获列表框中的MouseDown / Move / Up事件:

创建ListBox的子类,如下所示. 3种方法:

internal void MyOnMouseLeftButtonDown(MouseButtonEventArgs e)  
 protected override void OnMouseMove(MouseEventArgs e)  
 protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)

将被召唤,你可以随心所欲地做任何事情.有一个微妙的技巧是从不调用ListBox的OnMouseLeftButtonDown方法:您需要实现ListBoxItem的子类,您可以在其中处理此事件.

using System;
using System.Collections.Generic;
using System.Net;
using System.Windows;
using System.Windows.Controls;
using System.Windows.Documents;
using System.Windows.Ink;
using System.Windows.Input;
using System.Windows.Media;
using System.Windows.Media.Animation;
using System.Windows.Shapes;

namespace MyControls
{
  //In order for this class to be usable as a control, you need to create a folder
  //named "generic" in your project, and a "generic.xaml" file in this folder
  //(this is where you can edit the default look of your controls)
  //
  /*
   * Typical content of an "empty" generic.xaml file : 
    <ResourceDictionary
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    xmlns:local="clr-namespace:VideoControls">
    </ResourceDictionary>
   */
  public class MyListBox : ListBox
  {
    public MyListBox()
    {
        DefaultStyleKey = typeof(ListBox);
    }

    public override void OnApplyTemplate()
    {
      base.OnApplyTemplate();
    }

    #region ScrollViewer / unlocking access related code
    private ScrollViewer _scrollHost;
    public ScrollViewer ScrollViewer
    {
      get 
      {
        if (_scrollHost == null)
          _scrollHost = FindVisualChildOfType<ScrollViewer>(this);
        return _scrollHost; 
      }
    }

    public static childItemType FindVisualChildOfType<childItemType>(DependencyObject obj)
      where childItemType : DependencyObject
    {
      // Search immediate children first (breadth-first)
      for (int i = 0; i < VisualTreeHelper.GetChildrenCount(obj); i++)
      {
        DependencyObject child = VisualTreeHelper.GetChild(obj, i);

        if (child != null && child is childItemType)
          return (childItemType)child;

        else
        {
          childItemType childOfChild = FindVisualChildOfType<childItemType>(child);

          if (childOfChild != null)
            return childOfChild;
        }
      }

      return null;
    }
    #endregion

    //Modify MyListBox so that it uses MyListBoxItem instead of ListBoxItem
    protected override DependencyObject GetContainerForItemOverride()
    {
      MyListBoxItem item = new MyListBoxItem(this);
      if (base.ItemContainerStyle != null)
      {
        item.Style = base.ItemContainerStyle;
      }

      return item;
    }

    //OnMouseLeftButtonUp is never reached, since it is eaten by the Items in the list...
    /*
    protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
    {
      base.OnMouseLeftButtonDown(e);
      e.Handled = false;
    }
    */

    internal void MyOnMouseLeftButtonDown(MouseButtonEventArgs e)
    {
    }

    protected override void OnMouseMove(MouseEventArgs e)
    {
      base.OnMouseMove(e);
    }

    protected override void OnMouseLeftButtonUp(MouseButtonEventArgs e)
    {
      base.OnMouseLeftButtonUp(e);
    }


  }






  public class MyListBoxItem : ListBoxItem
  {
    MyListBox _customListBoxContainer;

    public MyListBoxItem()
    { }

    public MyListBoxItem(MyListBox customListBox)
    {
      this._customListBoxContainer = customListBox;
    }

    protected override void OnMouseLeftButtonDown(MouseButtonEventArgs e)
    {
      base.OnMouseLeftButtonDown(e);

      if (this._customListBoxContainer != null)
      {
        this._customListBoxContainer.MyOnMouseLeftButtonDown(e);
      }

    }
  }
}
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