Question

I have an ItemsControl that contains items that each has its own DataTemplate. Each ViewModel class in the ItemsSource derives from a common ancestor that has a Header property.

I want to wrap each item in a Expander control, but my problem is that I don’t know how to ‘carry over’ each ‘DataTemplate’ to the DataContext of the expading part of the Expander.

In code, my problem looks like this:

VieModels:

public class VM { public string Name { get; set; } }
public class VM1 : VM { public string Description { get; set; } }
public class VM2 : VM { public string Sakkie { get; set; } }

Items property on the code-behind (because it’s simple for the purpose of this question)

    public IEnumerable<VM> Items
    {
        get
        {
            yield return new VM1() { Name = "First VM1", Description = "First VM1 Description" };
            yield return new VM2() { Name = "Vm2, nr2", Sakkie = "sakkie sakkie boeredans" } ;
            yield break;
        }
    }

The XAML of the window:

<Window.Resources>
    <DataTemplate DataType="{x:Type local:VM1}">
        <local:VM1UC />
    </DataTemplate>
    <DataTemplate DataType="{x:Type local:VM2}">
        <local:VM2UC />
    </DataTemplate>
    <DataTemplate x:Key="DataTemplate1">
        <Expander Header="{Binding Name}">
            <ContentPresenter DataContext="{Binding DataContext, RelativeSource={RelativeSource TemplatedParent}}"/>
        </Expander>
    </DataTemplate>
</Window.Resources>
<ItemsControl ItemsSource="{Binding Items}" Background="LightCoral" ItemTemplate="{DynamicResource DataTemplate1}"/>

It looks like this, which is suprising, but understandable:

alt text http://img514.imageshack.us/img514/6937/itemscontrol.png

I am actually expecting the custom UserControls to show up in the expanded sections…

Answer 1

Instead of setting the DataContext, you should set the Content:

<ContentPresenter Content="{Binding DataContext, RelativeSource={RelativeSource TemplatedParent}}"/>

This will ensure the appropriate DataTemplate is resolved based on the type of the Content.