WPF TwoWay data binding limitation

Question

Is it safe to assume that WPF TwoWay data binding Wont work on controls which dont have focus ?

For example in the following code.

 <Window.Resources>
        <XmlDataProvider x:Key="TestBind1" XPath="/BindTest1">
            <x:XData>
                <BindTest1 xmlns="">
                    <Value1>True</Value1>
                </BindTest1>
            </x:XData>
        </XmlDataProvider>
    </Window.Resources>
    <StackPanel>
        <GroupBox>
            <StackPanel>
                <RadioButton Content="Value1" IsChecked="{Binding Source={StaticResource TestBind1},Mode=TwoWay, XPath=Value1}"/>
                <RadioButton Content="Value2"/>
            </StackPanel>
         </GroupBox>
        <Button Content="Analyse" Click="OnAnalyseClicked"/>

    </StackPanel>

When i click on the radiobutton Value2, the value of BindTest1/Value1 will remain true because radiobutton Value1 changed whilst it didnt have focus ?

Is this normal behaviour for WPF ? I am aware that i can avoid this by using various techniques, but i wanted to ask if this is normal or is my Xaml missing some parameter causing this problem.

Answer 1

Bindings will update regardless of whether or not controls have focus. My guess is that something else is wrong in your XAML.

Answer 2

Finally , i found an answer. Basically, the binding will break for RadioButtons because everytime you change its binding, the radiobuttons will change the checked state of other buttons in the group

I found the answer here, which is specialize the RadioButton and prevent the binding from being changed.

Sample class which i used to fix the binding.

 /// <summary>
    /// data bound radio button
    /// </summary>
    public class DataBoundRadioButton : RadioButton
    {
        /// <summary>
        /// Called when the <see cref="P:System.Windows.Controls.Primitives.ToggleButton.IsChecked"/> property becomes true.
        /// </summary>
        /// <param name="e">Provides data for <see cref="T:System.Windows.RoutedEventArgs"/>.</param>
        protected override void OnChecked(RoutedEventArgs e)
        {
            // Do nothing. This will prevent IsChecked from being manually set and overwriting the binding.
        }

        /// <summary>
        /// Called by the <see cref="M:System.Windows.Controls.Primitives.ToggleButton.OnClick"/> method to implement a <see cref="T:System.Windows.Controls.RadioButton"/> control's toggle behavior.
        /// </summary>
        protected override void OnToggle()
        {
            BindingExpression be = GetBindingExpression(RadioButton.IsCheckedProperty);
            Binding bind = be.ParentBinding;

            Debug.Assert(bind.ConverterParameter != null, "Please enter the desired tag as the ConvertParameter");

            XmlDataProvider prov = bind.Source as XmlDataProvider;
            XmlNode node = prov.Document.SelectSingleNode(bind.XPath);
            node.InnerText = bind.ConverterParameter.ToString();

        }
    }