Is it appropriate to cast ContentPresenter.Content to UIElement?

Question

Are there any situations where the content of a ContentPresenter will be some object other than a UIElement? Given that the field is declared as object rather than a UIElement, it seems possible that there would be. However, I cannot think of any situations where it would be, or even if it would be valid.

ContentPresenter presenter = GetTemplateChild(PART_Presenter) as ContentPresenter;
UIElement myElement = (UIElement)presenter.Content;
myElement.SomeUIMethod(); // possible InvalidOperationException?

You will get an InvalidCastException in the 2nd line, not and InvalidOperationException on the third — Nir, Dec 01 '09 at 09:36

score 6 · Accepted Answer · edited Aug 21 '13 at 02:44

I do it all the time - and the entire MVVM method is built on non-UIElement content, here is an example:

Create a class that isn't derived from UIElement, I'll call is MyViewModelClass in this example.

Create a Window and add this code

public partial class Window1 : Window
{
    public Window1()
    {
        DataContext = new MyViewModelClass();
        InitializeComponent();
    } 
}

And add some content control to the XAML:

<Button Content="{Binding}"/>

Now you have a ContentPresenter (inside the Button control template) with MyViewModelClass as the Content.

Another (maybe more common) example is ItemControl - let's take a ListBox for example, each ListBoxItem has a ContentPresenter that has whatever was in the list set to ItemsSource.

Thanks, I assumed that was the case – jeffora Dec 01 '09 at 23:03 — jeffora, Dec 01 '09 at 23:03

score 4 · Answer 2 · edited Aug 21 '13 at 02:44

4

Here's the most basic example I can think of

<Label Content="My Label" />

Now the content property is a string which doesn't derive from UIElement. So the short answer is yes, it's not only possible, it's likely to happen.

edited Aug 21 '13 at 02:44

Dave Clemmer

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answered Dec 01 '09 at 19:22

Bryan Anderson

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Is it appropriate to cast ContentPresenter.Content to UIElement?

2 Answers2