/// <summary>
/// 开始虚拟化子项
/// </summary>
private void BeginItemsVirtualizing(ScrollViewerView view, ScrollViewerView final)
{
Rect viewport = new Rect(view.HorizontalOffset - ScrollOwner.ViewportWidth * 0.5, view.VerticalOffset - ScrollOwner.ViewportHeight * 0.5, ScrollOwner.ViewportWidth * 2, ScrollOwner.ViewportHeight * 2);
foreach (var context in layoutContext)
{
bool IsBeginRealize = false;
foreach (var item in context.Elements)
{
if (item is IVirtualizingItem)
{
if (ShouldBeVirtualized(item, viewport))
{
(item as IVirtualizingItem).Virtualize();
if (IsBeginRealize)
{
break;
}
}
else
{
IsBeginRealize = true;
(item as IVirtualizingItem).Realize();
}
}
}
}
}
/// <summary>
/// 判断一个元素在指定的 ScrollViewerView 是否应该被虚拟化
/// </summary>
/// <param name="item">需要测量的元素</param>
/// <param name="view">指定的视图</param>
/// <returns></returns>
private bool ShouldBeVirtualized(UIElement item, ScrollViewerView view)
{
Rect arrange = GetArrange(item);
Rect viewport = new Rect(view.HorizontalOffset - ScrollOwner.ViewportWidth * 0.5, view.VerticalOffset - ScrollOwner.ViewportHeight * 0.5, ScrollOwner.ViewportWidth * 2, ScrollOwner.ViewportHeight * 2);
viewport.Intersect(arrange);
return(viewport == Rect.Empty);
}