asp.net-core - 如果不满足条件，则查看数据 Blazor

Question

我在 Blazor 中有一个服务文件，可以将文件上传到我的项目，但我正在尝试检查上传的文件是否只有 jpg 及其姐妹文件。但是，我注意到我不能使用 ViewData 来显示条件确实满足的消息。

这是服务

 public async Task Upload(IFileListEntry file)
        {

            var imgext = Path.GetExtension(file.Name);
            string Message = "Plesae upload only jpg, png, gif or jpeg";
            if (imgext == ".jpg" || imgext == ".png" || imgext == ".gif" || imgext == ".jpeg")
            {
                var path = Path.Combine(_oIWebHostEnvironment.ContentRootPath, "Images/UploadImages", file.Name);
                var memoryStram = new MemoryStream();

                await file.Data.CopyToAsync(memoryStram);

                using (FileStream fileStream = new FileStream(path, FileMode.Create, FileAccess.Write))
                {

                    memoryStram.WriteTo(fileStream);
                }
            }
            else
            {
                ViewData Message; // viewdata is not available
            }

**这是组件**

@code{
    @*Upload Feature Image*@

    IFileListEntry file;
    async Task HandelFileSelcted(IFileListEntry[] files)
    {
        var imgext = Path.GetExtension(file.Name);

        file = files.FirstOrDefault();

        if (file != null)
        {
            await fileUpload.Upload(file);

        }
    }

}