D：/Project/Asp.net/WebSite/Uploads / .....'是物理路径，但预计会有虚拟路径

Question

我有这个函数将文件保存到server.mappath。我在第if (!File.Exists(Server.MapPath(existsFile)))行中遇到的错误是：

  

'给出物理路径，预期虚拟路径'

代码：

protected void Upload(object sender, EventArgs e)
    {
        string directoryPath = @"~\Uploads\" + Session["userid"];      
        if (!Directory.Exists(HttpContext.Current.Server.MapPath(directoryPath)))
            Directory.CreateDirectory(HttpContext.Current.Server.MapPath(directoryPath));
        if (FileUpload1.HasFile)
        {
            HttpFileCollection hfc = Request.Files;
            for (int i = 0; i <= hfc.Count - 1; i++)    // CHECK THE FILE COUNT.
            {
                HttpPostedFile postedFile = hfc[i];
                if (postedFile.ContentLength > 0)
                {
                    string filename = Path.GetFileName(postedFile.FileName);
                    string contentType = postedFile.ContentType;
                    string existsFile = Server.MapPath(directoryPath)+"\\" + filename;
                    if (!File.Exists(Server.MapPath(existsFile)))
                        postedFile.SaveAs(Server.MapPath(directoryPath) + filename);
                }
            }
        }
        LoadUploadedFiles(ref this.GridViewFileList, directoryPath);
    }