Question

I have a user control that has a Title property bound to the Text property of a TextBlock:

XAML

<TextBlock Grid.Column="0" Text="{Binding ElementName=me,Path=Title}" HorizontalAlignment="Left" VerticalAlignment="Top" />

Code behind

public String Title
{
    get { return (String)GetValue(TitleProperty); }
    set { SetValue(TitleProperty, value); }
}

public static readonly DependencyProperty TitleProperty =
    DependencyProperty.Register("Title", typeof(String), typeof(ClosableTabHeader), new UIPropertyMetadata(""));

And I wish to bind this Title property to another property on the main window:

XAML

<my:ClosableTabHeader Title="{Binding ElementName=me,Path=ShortenAmount}" />

Code behind

public Int32 ShortenAmount
{
    get { return (Int32)GetValue(ShortenAmountProperty); }
    set { SetValue(ShortenAmountProperty, value); }
}

public static readonly DependencyProperty ShortenAmountProperty =
    DependencyProperty.Register("ShortenAmount", typeof(Int32), typeof(MainWindow), new UIPropertyMetadata(0));

However, the textblock does not update.

When I replace the usercontrol declaration with a TextBlock, however, it works fine:

<TextBlock Text="{Binding ElementName=me,Path=ShortenAmount}" />

While there are certainly workarounds, in terms of what I am trying to do itself, may I know where I went wrong?

Answer 1

Problem lies in your ElementName. From your code my:ClosableTabHeader is not named as me. me looks like your MainWindow. But you are using me and Title together in this binding…

   <TextBlock Grid.Column="0" Text="{Binding ElementName=me,Path=Title}"  
              HorizontalAlignment="Left" VerticalAlignment="Top" /> 

where Title is property from ClosableTabHeader and not MainWindow (well MainWindow.Title exists as a inbuilt WPF property but I am sure we are not talking about it)