private static TextBlock EnsureAdorner(TextBox textBox) {
var content = GetAdornerContent(textBox);
if (content != null) {
return (TextBlock)content;
}
var textBlock = new TextBlock {
Foreground = (Brush)textBox.FindResource(Brushes.GrayTextBrushKey),
Margin = new Thickness(2,0,0,0),
VerticalAlignment = VerticalAlignment.Center,
Visibility = string.IsNullOrEmpty(textBox.Text) ? Visibility.Visible : Visibility.Collapsed
};
textBox.TextChanged += (sender, args) => {
textBlock.Visibility = string.IsNullOrEmpty(textBox.Text) ? Visibility.Visible : Visibility.Collapsed;
};
SetAdornerContent(textBox, textBlock);
return textBlock;
}