The real show-stopper here is that when you use the Label
in a VisualBrush
, the label isn't part of the TextBox
' "Visual Tree" (see for example Sheldon Xiao's answer to this similar question on MSDN: Binding Problem inside VisualBrush).
This means that the label won't inherit the text box' DataContext
, and you can't reach the text box from a RelativeSource
binding either. In contrast, the accepted answer in your other post sets the actual content of a button, which does make the content part of the button's visual tree.
So I don't think there's a pure XAML solution to this problem - pushing the correct MyOptions.Default
from the text box to the label. One possible code-based solution is to scrap the TextBoxWithDefault
style and do everything from your attached property when Default
changes:
...
public static readonly DependencyProperty DefaultProperty =
DependencyProperty.RegisterAttached(
"Default",
typeof(string),
typeof(MyOptions),
//Listen for changes in "Default":
new PropertyMetadata(null, OnMyDefaultChanged));
private static void OnMyDefaultChanged(DependencyObject sender,
DependencyPropertyChangedEventArgs e)
{
var text = (TextBox)sender;
var myDefault = e.NewValue;
var defaultLabel = new Label();
defaultLabel.Foreground = Brushes.LightGray;
//Explicitly bind the needed value from the TextBox:
defaultLabel.SetBinding(Label.ContentProperty,
new Binding()
{
Source = text,
Path = new PropertyPath(MyOptions.DefaultProperty)
});
text.Background = new VisualBrush()
{
Visual = defaultLabel,
AlignmentX = AlignmentX.Left,
AlignmentY = AlignmentY.Center,
Stretch = Stretch.None
};
text.TextChanged += new TextChangedEventHandler(OnTextWithDefaultChanged);
}
private static void OnTextWithDefaultChanged(object sender,
TextChangedEventArgs e)
{
var text = (TextBox)sender;
var defaultLabel = (text.Background as VisualBrush).Visual as Label;
defaultLabel.Visibility = string.IsNullOrEmpty(text.Text) ?
Visibility.Visible :
Visibility.Collapsed;
}