public class DatePickerHelper    {        public static object GetWatermark(DependencyObject obj)        {            return (object)obj.GetValue(WatermarkProperty);        }        public static void SetWatermark(DependencyObject obj, object value)        {            obj.SetValue(WatermarkProperty, value);        }        // Using a DependencyProperty as the backing store for Watermark.  This enables animation, styling, binding, etc...        public static readonly DependencyProperty WatermarkProperty =            DependencyProperty.RegisterAttached("Watermark", typeof(object), typeof(DatePickerHelper),                new FrameworkPropertyMetadata(null,                    new PropertyChangedCallback(OnWatermarkChanged)));        private static void OnWatermarkChanged(DependencyObject d, DependencyPropertyChangedEventArgs e)        {            var datePicker = d as DatePicker;            if (datePicker == null)                return;            if (datePicker.IsLoaded)            {                SetWatermarkInternal(datePicker, e.NewValue);            }            else            {                RoutedEventHandler loadedHandler = null;                loadedHandler = delegate                {                    datePicker.Loaded -= loadedHandler;                    SetWatermarkInternal(datePicker, e.NewValue);                };                datePicker.Loaded += loadedHandler;            }        }        private static void SetWatermarkInternal(DatePicker d, object value)        {            var textBox = d.Template.FindName("PART_TextBox", d) as Control;            if (textBox != null)            {                var watermarkControl = textBox.Template.FindName("PART_Watermark", textBox) as ContentControl;                if (watermarkControl != null)                    watermarkControl.Content = value;            }        }    }