为什么ItemsControl不使用我的ItemTemplate? [英] Why Does ItemsControl Not Use My ItemTemplate?

问题描述

我能够在ItemsControl中使用ItemTemplate来以特定格式呈现项目.但是，如果ItemsControl中的某个项目恰好是一个TextBox，则将呈现该TextBox而不是ItemsTemplate的实例.据我所知，对于任何FrameworkElement都是如此.这是ItemsControl的预期行为，还是我做错了什么?

I am able to use an ItemTemplate within an ItemsControl to render items in a specific format. However, if one of the items within the ItemsControl happens to be, say, a TextBox, that TextBox is rendered rather than an instance of the ItemsTemplate. From what I can tell, this is true for any FrameworkElement. Is this intended behavior for an ItemsControl, or am I doing something incorrectly?

一个例子:

<ItemsControl>
  <ItemsControl.ItemTemplate>
    <DataTemplate>
      <Grid Margin="5">
        <Rectangle Fill="Blue" Height="20" Width="20" />
      </Grid>
    </DataTemplate>
  </ItemsControl.ItemTemplate>
  <ItemsControl.Items>
    <sys:Object />
    <TextBox />
    <sys:Object />
    <Rectangle Fill="Red" Height="20" Width="20" />
  </ItemsControl.Items>
</ItemsControl>

我希望它显示四个蓝色矩形.我认为，每当定义了ItemTemplate时，集合中的每个项目都将呈现为模板的实例.但是，在这种情况下，将呈现以下内容:蓝色矩形，然后是TextBox，然后是蓝色矩形，再是红色矩形.

I expected this to display four blue rectangles. I thought that any time an ItemTemplate has been defined each item in the collection is rendered as an instance of the template. However, in this case the following is rendered: a blue rectangle followed by a TextBox followed by a blue rectangle followed by a red rectangle.

推荐答案

ItemsControl具有受保护的成员IsItemItsOwnContainerOverride，该成员被传递了items集合中的对象，如果该对象可以直接添加到true，则返回true.项目面板中没有生成容器(并因此而成为模板).

The ItemsControl has a protected member IsItemItsOwnContainerOverride which is passed an object from the items collection and returns true if that object can be added directly to the items panel without a generated container (and thereby be templated).

对于从UIElement派生的任何对象，基本实现均返回true.

The base implementation returns true for any object that derives from UIElement.

要获得预期的行为，您将需要从ItemsControl继承并覆盖此方法，并使该方法始终返回false.不幸的是，这还没有结束.如果该项是UIElement，则PrepareContainerForItemOverride的默认实现仍不会将ItemTemplate分配给容器，因此您也需要覆盖此方法:-

To get the behaviour you would expect you would need to inherit from ItemsControl and override this method and have it always return false. Unfortunately thats not the end of the matter. The default implementation of PrepareContainerForItemOverride still doesn't assign the ItemTemplate to the container if the item is a UIElement so you need to override this method as well:-

    protected override bool IsItemItsOwnContainerOverride(object item)
    {
        return false;
    }


    protected override void PrepareContainerForItemOverride(DependencyObject element, object item)
    {
        base.PrepareContainerForItemOverride(element, item);
        ((ContentPresenter)element).ContentTemplate = ItemTemplate;
    }

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