Question

I am trying to write a UserControl that will allow both single controls in it (like Label), as well as “layout” controls like StackPanel and friends.

I am having trouble doing that. The code I have works for single controls, but not for layout controls. I have a feeling this is an obvious fix, I am new to WPF. Here is the UserControl XAML:

<UserControl <!-- namespaces omitted for brevity -->>
    <UserControl.ContentTemplate>
        <DataTemplate>
            <ContentPresenter Content="{TemplateBinding Content}" />
        </DataTemplate>
    </UserControl.ContentTemplate>
</UserControl>

When I try to use it like this:

<my:SpecialUserControl>
    hello
</my:SpecialUserControl>

It’s fine. But when I try to do something like

<my:SpecialUserControl>
    <StackPanel>
        <!-- stuff -->
    </StackPanel>
</my:SpecialUserControl>

I get an error in Visual Studio Intellisense saying

The specified value cannot be assigned to the collection. The following type was expected: UIElement

And when I run the app (it builds), I get this exception at that place in the XAML:

‘Add value to collection of type System.Windows.Controls.UIElementCollection threw an exception.’ Line number x and line position y.

What can I do to make my UserControl able to accept any type of content?

Answer 1

The ContentPresenter should be a part of the ControlTemplate (<UserControl.Template>) of your control, not inside your ContentTemplate. I think that could be your problem.