c# 跨线程访问窗体UI

struct ImgInfo
{
    public string url;
    public string path;
};

ImgInfo img1;  //定义一个结构体，用于向线程中传递下载的参数
img1.url = s1;
img1.path = path;

Thread thread1 = new Thread(new ParameterizedThreadStart(DownImg));
thread1.Start(img1);

 private void DownImg(object img)
 {
    ImgInfo img1 = (ImgInfo)img;
    WebClient wc1 = new WebClient();
    if (L1.InvokeRequired) 
    {
       this.BeginInvoke(new Action<string>((x) => { L1.Items.Add(x.ToString()); }), "正在下载-->   "+img1.url);
    }

    wc1.DownloadFileAsync(new Uri(img1.url), img1.path);  
 }