asp.net – ViewState支持的属性不适用于列表

[Serializable]
    public class UploadedFile
    {
      public string FileName { get; set; }
      public Guid FileGuid { get; set; }
    }

    public List<UploadedFile> UploadedFiles
    {
      get
      {
        return (List<UploadedFile>) (ViewState["UploadedFiles"] ?? new List<UploadedFile>());
      }
      set
      {
        ViewState["UploadedFiles"] = value;
      }
    }

当我尝试将项添加到列表时,UploadedFiles.Count保持为零：

var uploadedFile = new UploadedFile {FileName = args.FileName, FileGuid = args.FileGuid};
UploadedFiles.Add(uploadedFile); // UploadedFiles.Count == 0 here!

有人有想法吗？

public List<UploadedFile> UploadedFiles     
{       
    get       
    {         
         var list = (List<UploadedFile>) (ViewState["UploadedFiles"] ?? 
             new List<UploadedFile>()); 
         ViewState["UploadedFiles"] = list;
         return list;      
    }       
    set       
    {         
        ViewState["UploadedFiles"] = value;       
    }     
}