为什么ItemContainerGenerator返回null？

Question

我有一个ListBox,我需要将其ControlTemplate设置为Virtualizing WrapPanel,它是一个扩展VirtualizingPanel的类,使用如下所示的样式:

<Style TargetType="{x:Type ListBox}" x:Key="PhotoListBoxStyle">
                <Setter Property="Foreground" Value="White" />
                <Setter Property="Template">
                    <Setter.Value>
                        <ControlTemplate  TargetType="{x:Type ListBox}" >
                            <s:VirtualizingVerticalWrapPanel>
                            </s:VirtualizingVerticalWrapPanel>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </Style>

现在,在下面虚拟化WrapPanel的私有方法中,我尝试访问this.ItemContainerGenerator,但我得到null值,任何想法是什么问题？

private void RealizeFirstItem()
{
    IItemContainerGenerator generator = this.ItemContainerGenerator;
    GeneratorPosition pos = generator.GeneratorPositionFromIndex(0);

    using (generator.StartAt(pos, GeneratorDirection.Forward))
    {
        UIElement element = generator.GenerateNext() as UIElement;

         generator.PrepareItemContainer(element);

                    this.AddInternalChild(element);
    }
 }

Answer 1

我想我遇到了类似的问题,这有助于:

var necessaryChidrenTouch = this.Children;
IItemContainerGenerator generator = this.ItemContainerGenerator;

...出于某种原因,您必须"触摸"子集合才能使ItemContainerGenerator正确初始化.