WPF：间接支持虚拟化的ListBox

/// <summary>
/// 间接实现了虚拟化的ListBox
/// 子项必须实现IVisible接口
/// 你可以在IsVisible发生改变时实现一系列自定义动作
/// 比如：当IsVisible = false时，清空子项的内容；当IsVisible = true时，还原子项的内容
/// </summary>
public class VirtualizedListBox : ListBox
{
private ScrollViewer scrollViewer; public override void OnApplyTemplate()
{
scrollViewer = FindVisualChild<ScrollViewer>(this);
if (scrollViewer != null)
{
scrollViewer.ScrollChanged -= OnScrollChanged;
scrollViewer.ScrollChanged += OnScrollChanged;
}
} #region 事件
/// <summary>
/// 滚动条滚动事件
/// </summary>
/// <param name="sender"></param>
/// <param name="e"></param>
private void OnScrollChanged(object sender, ScrollChangedEventArgs e)
{
foreach (IVisible item in this.Items)
{
var listBoxItem = (FrameworkElement)this.ItemContainerGenerator.ContainerFromItem(item);
item.IsVisible = IsChildVisibleInParent(listBoxItem, scrollViewer);
}
}
#endregion #region 私有方法
/// <summary>
/// 判断子控件是否在父控件中可见
/// </summary>
/// <param name="child">子控件</param>
/// <param name="parent">父控件</param>
/// <returns></returns>
private bool IsChildVisibleInParent(FrameworkElement child, FrameworkElement parent)
{
var childTransform = child.TransformToAncestor(parent);
var childRectangle = childTransform.TransformBounds(new Rect(new Point(, ), child.RenderSize));
var ownerRectangle = new Rect(new Point(, ), parent.RenderSize);
return ownerRectangle.IntersectsWith(childRectangle);
} public static T FindVisualChild<T>(DependencyObject obj) where T : DependencyObject
{
if (obj != null)
{
for (int i = ; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null && child is T)
{
return (T)child;
}
T childItem = FindVisualChild<T>(child);
if (childItem != null) return childItem;
}
}
return null;
}
#endregion
}

/// <summary>
/// 表示可见的类型
/// </summary>
public interface IVisible
{
/// <summary>
/// 是否可见
/// </summary>
bool IsVisible
{
get;
set;
}
}

public static T FindVisualChild<T>(DependencyObject obj) where T : DependencyObject
{
if (obj != null)
{
for (int i = ; i < VisualTreeHelper.GetChildrenCount(obj); i++)
{
DependencyObject child = VisualTreeHelper.GetChild(obj, i);
if (child != null && child is T)
{
return (T)child;
}
T childItem = FindVisualChild<T>(child);
if (childItem != null) return childItem;
}
}
return null;
}