1，在XML中绑定

xmlns:toolBox="clr-namespace:EBookApp.ToolBox"

<Image x:Name="imageShort" Stretch="Fill" Width="50" d:LayoutOverrides="HorizontalMargin"
                       Source="{Binding RelativeSource={RelativeSource AncestorType=toolBox:ResDetailItemControl},Path=Thumbnail}"/>

public static readonly DependencyProperty ThumbnailProperty =
            DependencyProperty.Register("Thumbnail",typeof(string),typeof(ResDetailItemControl),new PropertyMetadata("../Images/img.png"));

        public string Thumbnail
        {
            get { return (string)GetValue(ThumbnailProperty); }
            set { SetValue(ThumbnailProperty,value); }
        }