附加属性指定图片地址

public static void SetUrlSource(DependencyObject dependencyObject, string value)
        {
            dependencyObject.SetValue(UrlSourceProperty, value);
        }

        public static string GetUrlSource(DependencyObject dependencyObject)
        {
            return (string)dependencyObject.GetValue(UrlSourceProperty);
        }

        // Using a DependencyProperty as the backing store for UrlSource.  This enables animation, styling, binding, etc...
        public static readonly DependencyProperty UrlSourceProperty =
            DependencyProperty.RegisterAttached("UrlSource", typeof(string), typeof(ImageSource), new PropertyMetadata("", new PropertyChangedCallback(SetSource)));

        private static void SetSource(DependencyObject o, DependencyPropertyChangedEventArgs e)
        {
            Image images = o as Image;
            if (images != null)
            {
                Uri u = new Uri(Application.Current.Host.Source, e.NewValue.ToString());

                BitmapImage imgsrc = new BitmapImage(u);

                images.Source = imgsrc;
            }
        }