Window binding the DataContext to the window itself in WPF

Question

I have a simple dialog box that inherits from Window, and I set its DataContext in XAML as follows:

<Window x:Class="MyProject.MyDialog"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        DataContext="{Binding RelativeSource={RelativeSource Self}}"
        ...>
    <StackPanel>
        <TextBox Text="{Binding SomeText}"/>
        ...
    </StackPanel>
</Window>

and here, as I show this dialog box:

var dialog = new MyWindow();
MyWindow.SomeText = "some text";

if (dialog.ShowDialog() == true)
    ...

For some reason, this does not set the source text of the text field to "some text" when creating the window and there are no binding errors.

However, if I set the data context for the StackPanel instead of the window:

<StackPanel DataContext="{Binding RelativeSource={RelativeSource AncestorType=Window}}">
    ...
</StackPanel>

everything works as expected.

What is the difference between the two? Why doesn't the first approach work?

Answer 1

You need to implement INotifyPropertyChanged in your window to make the first case work.

(self) , , dc .