Binding in ContentControl Crash

Question

Can anyone tell me why this crashes my app? There seems to be some endless recursion by I can't figure out why. I get this exception

Logical tree depth exceeded while traversing the tree. This could indicate a cycle in the tree

<ContentControl Content="{Binding}">
    <ContentControl.ContentTemplate>
        <DataTemplate>
            <Button Content="{Binding MyString}"/>
        </DataTemplate>
    </ContentControl.ContentTemplate>
</ContentControl>

And this is all I have as Source

    public MainWindow()
    {
        InitializeComponent();
        MyString = "Test";
        this.DataContext = this;
    }

    public string MyString { get; set; }

Abstergent

Answer 1

You're using MainWindow as the DataContext of the MainWindow's content. When you set Content="{Binding}" on the ContentControl this is setting the ContentControl's content to the MainWindow instance. This is a problem because the ContentControl is contained in the MainWindow's Content. Whenever a Content property receives a UIElement, it renders it as a UIElement, not through the DataTemplate as it would with an non-UI class. So your tree ends up being

MainWindow
 ContentControl
  MainWindow
   ContentControl
    ...

Using a separate data object for your DataContext instead of the window itself will give you the behavior you're looking for:

public partial class Window13 : Window
{
    public Window13()
    {
        InitializeComponent();
        MyData data = new MyData();
        data.MyString = "Test";
        this.DataContext = data;
    }
}

public class MyData
{
    public string MyString { get; set; }
}

Lammers

John, you're the man!! Works like a charm :) I can finally put this problem behind me and I also know the reason thanks to your very clear explanation! Thanks and merry christmas – Abstergent

Answer 2

Although I totally agree with the accepted answer that you should not do this, sometimes you just don't have the choice. For instance, I'm using Xceed PropertyGrid and the DataContext I have for each item of the grid is a PropertyItem which is a UIElement (containing the actual data in a Value member).

The workaround I found is to use a ContentPresenter instead of a ContentControl. The documentation is not clear about this but it seems that UIElement are templated instead of being used as-is.

<ContentPresenter Content="{Binding}">
    <ContentPresenter.ContentTemplate>
        <DataTemplate>
            <Button Content="{Binding MyString}"/>
        </DataTemplate>
    </ContentPresenter.ContentTemplate>
</ContentPresenter>

Protolithic

Answer 3

You should remove the binding on the Content property of the ContentControl. What is this supposed to do anyway?

Office

My understand of the ContentControl is that the DataContext within the DataTemplate is the Content of the ContentControl and not the DataContext. So if I remove it I don't get a DataContext within the DataTemplate to bind to at all. Any ideas? – Abstergent