如何将IFormFile作为ViewModel对象的一部分发送到Web API

Question

我有带有以下控制器的.NET Core Web App：

    [HttpPost]
    public async Task<IActionResult> Update(StudentDetailsViewModel vm)
    {           
        var tokenNo = HttpContext.Session.GetString("Token");
        vm.ID = Convert.ToInt32(HttpContext.Session.GetString("StudentId"));

        HttpClient client = new HttpClient();
        client.DefaultRequestHeaders.Authorization = new AuthenticationHeaderValue("Bearer", tokenNo);
        client.DefaultRequestHeaders.Accept.Clear();
        client.DefaultRequestHeaders.Accept.Add(new MediaTypeWithQualityHeaderValue("application/json"));

        var putStudentUrl = _appSettings.Value.Apis.GSRTCApi.Url + _appSettings.Value.Apis.GSRTCApi.StudentsEndpoint + vm.ID;

        var settings = new JsonSerializerSettings();

        var stringData = JsonConvert.SerializeObject(vm); 

        var contentData = new StringContent(stringData, Encoding.UTF8, "application/json");

        var response = await client.PutAsync(putStudentUrl, contentData); // contentData);


        return RedirectToAction("Index", "Home");
    }

控制器调用我的Web API，一切正常，直到我通过html表单上传文件。发生这种情况时，将在客户端的StudentDetailsViewModel的IFormFile属性中拾取该文件，但是当进行API调用时，整个对象为null。API控制器是：

[HttpPut("{id}")]
public async Task<IActionResult> Put(int? id, [FromBody]StudentViewModel student)
{
    // API operations here
} 

我怀疑我没有正确地序列化StudentDetailsViewModel对象，因为我有一个属性IFormFile，它是一个接口。但是，我不确定到底该如何自定义Json.Newsoft对象。

Answer 1

对于发送IFormFile，您需要使用FromForm删除FromBody和时的默认值MultipartFormDataContent。

这是完整的步骤：

1. 网络应用模型

public class StudentDetailsViewModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public IFormFile File { get; set; }
}

2. Web App控制器

public async Task<IActionResult> Update(StudentDetailsViewModel vm)
{

    HttpClient client = new HttpClient();
    var putStudentUrl = @"url";
    byte[] data;
    using (var br = new BinaryReader(vm.File.OpenReadStream())) 
    {
        data = br.ReadBytes((int)vm.File.OpenReadStream().Length);
    }
    ByteArrayContent bytes = new ByteArrayContent(data);
    MultipartFormDataContent multiContent = new MultipartFormDataContent();
    multiContent.Add(bytes, "file", vm.File.FileName);
    multiContent.Add(new StringContent(vm.Id.ToString()),"Id");
    multiContent.Add(new StringContent(vm.Name), "Name");
    var response = await client.PutAsync(putStudentUrl, multiContent); 
    return RedirectToAction("Index", "Home");
}

3. Web API模型

public class StudentViewModel
{
    public int Id { get; set; }
    public string Name { get; set; }
    public IFormFile File { get; set; }
}

4. Web API控制器

[HttpPut("{id}")]
public async Task<IActionResult> Put(int? id,StudentViewModel student)
{
    using (var stream = new FileStream(@"file path", FileMode.Create))
    {
        await student.File.CopyToAsync(stream);
    }
    return Ok();
}

注意multiContent.Add(bytes, "file", vm.File.FileName);，第二个参数是IFormFile字段的名称。