如何创建 IFormFile 图像文件并将其发送到视图中的输入元素？

Question

我的视图中有一个带有输入元素的表单。

<input asp-for="Image" id="mainImageInput" type="file" onchange="readURL(this,'mainImage')" accept="image/jpeg, image/png" class="form-control"/>

我将我所有的图像作为 byte[] 存储在数据库中。如何将 byte[] 转换为 IFormFile 并将其发送到输入元素中的视图？不，我不是在问如何显示图像，我想将它直接插入到输入元素中，就像用户使用“浏览”选择它一样。

我试过写这个，但它不起作用：

var ad = _context.Advertisements
            .Select(x => new {
                Id = x.Id,
                Title = x.Title,
                Description = x.Description,
                Price = x.Price,
                Location = x.Location,
                CategoryId = x.CategoryId,
                ImageInBase64 = Convert.ToBase64String(x.Image),
                UserId = x.UserId,
                ImageInByteArray=x.Image
            })
            .FirstOrDefault(x=>x.Id==id);

IFormFile file = null;
using (var stream = new MemoryStream(ad.ImageInByteArray))
{
    file = new FormFile(stream, 0, ad.ImageInByteArray.Length, "name", "fileName");
}

var viewModel = new AdvertisementViewModel()
            {
                Id = ad.Id,
                Title = ad.Title,
                Description = ad.Description,
                Price = ad.Price,
                Location = ad.Location,
                CategoryId = ad.CategoryId,
                ImageInBase64 = ad.ImageInBase64,
                UserId = ad.UserId,
                Image = file
            };
return View("Edit",viewModel);

这是提交表单后我应该收到图片的操作，所有其他属性都在那里，但我得到的图片为空。

        [HttpPost]
        [ValidateAntiForgeryToken]
        [Authorize]
        public async Task<IActionResult> Edit(AdvertisementViewModel viewModel) 
        {
            // viewmodel.Image is null, so my model state will always be invalid
            // need a workaround

            if (!ModelState.IsValid)
            {
                return View(viewModel);
            }
        }

Answer 1

And no, I am not asking how to display the image, I want to insert it directly into the input element as if the user has selected it using "Browse".

由于浏览器中的安全原因，我认为我们不能将值设置为 <input type='file' />。

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