WPF TargetUpdated event not firing on ContentControl - wpf

Question

I'm using an attached property to subscrive to the TargetUpdated event from a TextBlock, so I can be notified every time the text changes.
Using the following XAML:
<DataTemplate DataType="{x:Type targetUpdatedApp:Item}">
<targetUpdatedApp:LabelControl Text="{Binding Text, NotifyOnTargetUpdated=True}" Style="{StaticResource LabelTemplateStyle}"/>
</DataTemplate>
</Window.Resources>
<StackPanel>
<ListBox ItemsSource="{Binding Items}">
<!--<ListBox.ItemTemplate>
<DataTemplate>
<TextBlock Text="{Binding Text, NotifyOnTargetUpdated=True}" targetUpdatedApp:DesiredWidth.DesiredMinWidth="120"/>
</DataTemplate>
</ListBox.ItemTemplate>-->
</ListBox>
<Button Click="ButtonBase_OnClick">Button</Button>
</StackPanel>
Here is my AttachedProperty code:
public class DesiredWidth
{
public static readonly DependencyProperty DesiredMinWidthProperty =
DependencyProperty.RegisterAttached(
"DesiredMinWidth", typeof (double),
typeof (TextBlock), new PropertyMetadata(OnDesiredMinWidthChanged));
public static double GetDesiredMinWidth(DependencyObject obj)
{
return (double) obj.GetValue(DesiredMinWidthProperty);
}
public static void SetDesiredMinWidth(DependencyObject obj, double value)
{
obj.SetValue(DesiredMinWidthProperty, value);
}
static void OnDesiredMinWidthChanged(DependencyObject obj, DependencyPropertyChangedEventArgs args)
{
var textBlock = obj as TextBlock;
if (textBlock == null)
{
return;
}
if (args.NewValue != null)
{
textBlock.TargetUpdated += OnTextBoxTargetUpdated;
}
}
static void OnTextBoxTargetUpdated(object sender, System.Windows.Data.DataTransferEventArgs e)
{
if (e.Property == TextBlock.TextProperty)
{
}
}
}
The Items collection binded to the ListBox is an ObservableCollection and the items on it implement INotifyPropertyChanged.
If I uncomment the code of the ListBox.ItemTemplate and use it instead of the style it works ok, but I use LabelControl (which basically has a Text DependencyProperty) described on the style the TargetUpdated event subscribed on the AttachedProperty never gets fired.
Could someone give me some help on this issue?
Thanks in advance.
PS: Added from comment :
<Style x:Key="LabelTemplateStyle" TargetType="{x:Type argetUpdatedApp:LabelControl}">
<Setter Property="Template">
<Setter.Value>
<ControlTemplate TargetType="{x:Type targetUpdatedApp:LabelControl}">
<TextBlock Text="{TemplateBinding Text}" TargetUpdatedApp:DesiredWidth.DesiredMinWidth="120"/>
</ControlTemplate>
</Setter.Value>
</Setter>
</Style>

Answer 1

NotifyOnTargetUpdated will only apply to the binding that it's set on, not bindings on elements contained within. You have this set on the LabelControl, but the event handler is attached to the TextBlock inside its ControlTemplate, which isn't notifying. Use:
<ControlTemplate TargetType="{x:Type targetUpdatedApp:LabelControl}">
<TextBlock Text="{TemplateBinding Text, NotifyOnTargetUpdated=True}" targetUpdatedApp:DesiredWidth.DesiredMinWidth="120"/>
</ControlTemplate>
Another way you could do this, which wouldn't require you to edit bindings, is to use another attached property instead of the element's own Text property:
<TextBlock DesiredWidth.Text="{Binding Text}" DesiredWidth.MinWidth="120" />
And in DesiredWidth you could then add a OnTextChanged callback that passes the value on to the TextBlock's Text and does any other handling needed.