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itemscontrol itemtemplate silverlight wpf

Why Does ItemsControl Not Use My ItemTemplate?

发布于 2020-05-27 13:59:42

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?

An example:

<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>

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.

Questioner
Drew
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AnthonyWJones 2010-10-02 19:32

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).

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

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;
    }
Glenn Slayden 1970-01-01 08:00:00

As of 2015, they might have fixed the second part. With WPF in .NET 4.5.1, if I return false for IsItemItsOwnContainerOverride, then the template appears to be set on the item container.

Sheridan 1970-01-01 08:00:00

I didn't need the PrepareContainerForItemOverride override either in .NET 4.

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