为什么 ItemContainerGenerator 返回 null? [英] Why does ItemContainerGenerator return null?

问题描述

我有一个 ListBox，我需要将它的 ControlTemplate 设置为 Virtualizing WrapPanel，它是一个扩展 VirtualizingPanel 的类，使用的样式如下所示:

I have a ListBox, and I need to set its ControlTemplate to a Virtualizing WrapPanel which is a class that extends VirtualizingPanel, using a style that looks like this:

<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 Virtualizing WrapPanel 的私有方法中，我尝试访问 this.ItemContainerGenerator，但我得到了 null 值，不知道是什么问题??

Now, in the private method of Virtualizing WrapPanel below I try to access this.ItemContainerGenerator, but I get null value, any idea what's the problem ??

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);
    }
 }

推荐答案

我想我遇到了类似的问题，这对我有帮助:

I think I had a similar problem and this helped:

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

...出于某种原因，您必须触摸"子集合，以便 ItemContainerGenerator 正确初始化.

... for some reason you have to "touch" the children collection in order for the ItemContainerGenerator to initialize properly.

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