WPF Binding not updating with UpdateSourceTrigger=PropertyChanged

Question

I have a TabControl in which I set the DataContext to an instance of the this class, It's basicly a wrapper for DependencyProperties of a static class with the same properties.

In my Markup I set the DataContext like this

<TabControl DataContext="{Binding ElementName=self, Path=Settings}">

and binding to the property within the TabControl like this

<TextBox Text="{Binding Path=Url, Mode=TwoWay, UpdateSourceTrigger=PropertyChanged}" />

However, this does not lead to any updates of the source when the content of the TextBox is changed. I can change the content of the TextBox, let it loose focus etc. it does just not update the source.

Check output window. Do you see any binding errors over there? — Rohit Vats, Aug 14 '14 at 17:50

score 0 · Answer 1 · answered Aug 14 '14 at 18:21

Url is a dependency property and when set from XAML, wrapper property setter won't be called.

From MSDN:

The current WPF implementation of its XAML processor is inherently dependency property aware. The WPF XAML processor uses property system methods for dependency properties when loading binary XAML and processing attributes that are dependency properties. This effectively bypasses the property wrappers. When you implement custom dependency properties, you must account for this behavior and should avoid placing any other code in your property wrapper other than the property system methods GetValue and SetValue.

In case you want to do something on its property changed you should provide PropertyChangedCallback and write code there.

You can refer to the sample here in case PropertyChangedCallback is new to you. Something like:

public static readonly DependencyProperty UrlProperty = 
  DependencyProperty.Register(
  "Url",
  typeof(string),
  typeof(SettingsWrapper),
  new PropertyMetadata(OnUrlChanged)
  )
);

private static void OnUrlChanged(DependencyObject d,
                                 DependencyPropertyChangedEventArgs e)
{
    SettingsWrapper instance = (SettingsWrapper)d;
    instance.Settings.Url = e.NewValue.ToString();
}

Hi, thanks for the answer! I tried it, but sadly it doesn't change anything on the behavior =/ — skeleten, Aug 14 '14 at 20:26

score 0 · Answer 2 · edited May 23 '17 at 12:05

0

You said in a (now deleted) comment that your Window has x:Name="self", however the Window class does not have a property called Settings.

If this is an attached property, you need to reference it by the attached property by the full name, and wrap it in parenthesis.

For example,

<TabControl DataContext="{Binding ElementName=self, Path=(local:MyClass.Settings)}">

See WPF Attached Property Data Binding for more info.

edited May 23 '17 at 12:05

Community

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answered Aug 14 '14 at 18:41

Rachel

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I also said that I have a property Settings within my Window-Code – skeleten Aug 14 '14 at 20:36
@skeleten The `` class does not have a property called `Settings`, so WPF will not be able to resolve the binding. If it is an attached property, you have to use the correct attached property syntax for binding purposes. You could also try setting the Window.DataContext to the Window object itself (`this.DataContext = this` in the constructor), and binding to `DataContext.Settings`, and that should work. – Rachel Aug 14 '14 at 20:44

WPF Binding not updating with UpdateSourceTrigger=PropertyChanged

2 Answers2