wpf 拖图片到窗体

前台代码：
<Window x:Class="拖拽.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
        Title="MainWindow" Height="350" Width="525"   AllowDrop="True" Drop="Photo_Drop">
    <Grid>
        <Border x:Name="borderImage" Width="258" Height="211" HorizontalAlignment="Right"   VerticalAlignment="Top" Background="LightGreen" CornerRadius="5,5,5,5" Margin="0,88,95,0">
          <Grid Height="180" Width="228">
            <TextBlock Margin="18,24,19,32" HorizontalAlignment="Center" VerticalAlignment="Center" Text="Drag a photo here" Width="80" TextAlignment="Center" TextWrapping="WrapWithOverflow" FontFamily="Agency FB" FontSize="15" FontWeight="Normal"/>
            <Image x:Name="photoSrc" Margin="4,4,6,6" Stretch="Fill" />
          </Grid>
        </Border>
    </Grid>
</Window>

后台代码：
 string photoPath;
        private void Photo_Drop(object sender, DragEventArgs e)
        {
            //设置窗体的 AllowDrop="True" Drop="Photo_Drop"
            //获取文件的全路径
            string[] fileNames = e.Data.GetData(DataFormats.FileDrop, true) as string[];
            string[] format = new string[5] {"jpg","png","gif","ico","bmp"};
            if (fileNames.Length > 0)
            {
                string[] path = fileNames[0].Split('.');
                string name = (path[path.Length - 1].ToString()).ToLower (); 
                //检索是否是给定的格式
                bool b = format.Contains<string>(name);
                if (b == true)
                {
                    photoPath = fileNames[0];
                    //给image控件设置数据源
                    photoSrc.Source = new BitmapImage(new Uri(photoPath));
                }
                else
                {

                }
            }
            e.Handled = true;
        }