C# 无法同时发布元数据和多部分。收到400个错误请求

我正试图从我的UWP应用程序上传一个文件，并在查询参数（下面的代码）中添加一些JSON数据。但是，我收到了一个错误的请求。不知道我错过了什么。但是，我能从邮递员那里得到同样的结果，得到200分

有人能帮忙吗

        string apiUrl = BuildUrl(url, apiContext);

        // req params which has the json string as key value pair and few other request parameters
        Uri uri = BuildUriWithQueryParams(apiUrl, reqParams);

        HttpRequestMessage reqMsg = new HttpRequestMessage(HttpMethod.Post, uri);

        // File upload
        if (files != null && files.Count > 0)
        {
            HttpMultipartFormDataContent formDataContent = new HttpMultipartFormDataContent();
            foreach (StorageFile storageFile in files)
            {
                var inputStream = await storageFile.OpenAsync(FileAccessMode.Read);
                HttpStreamContent httpStreamContent = new HttpStreamContent(inputStream);
                formDataContent.Add(httpStreamContent, "doc", storageFile.Name);
            }
            reqMsg.Content = formDataContent;
        }
        var response = await HttpClient.SendRequestAsync(reqMsg);//.AsTask(cts.Token);

---

从查询参数中删除JSON req参数并将其添加到HttpStringContent解决了这个问题。下面提到了所需的更改

 string apiUrl = BuildUrl(url, apiContext);

        // req params which has the json string as key value pair and few other request parameters
//    Uri uri = BuildUriWithQueryParams(apiUrl, reqParams);
      UriBuilder uriBuilder = new UriBuilder(apiUrl);

        HttpRequestMessage reqMsg = new HttpRequestMessage(HttpMethod.Post, uriBuilder .Uri);

        HttpMultipartFormDataContent formDataContent = new HttpMultipartFormDataContent();

        // File upload
        if (files != null && files.Count > 0)
        {
            foreach (StorageFile storageFile in files)
            {
                var inputStream = await storageFile.OpenAsync(FileAccessMode.Read);
                HttpStreamContent httpStreamContent = new HttpStreamContent(inputStream);
                formDataContent.Add(httpStreamContent, "doc", storageFile.Name);
            }
        }
            foreach (KeyValuePair<string, string> keyValuePair in reqParams)
                formDataContent.Add(new HttpStringContent(keyValuePair.Value), keyValuePair.Key);
            reqMsg.Content = formDataContent;

        var response = await HttpClient.SendRequestAsync(reqMsg);//.AsTask(cts.Token);

string apirl=BuildUrl（url，apiContext）；
//req参数，其中json字符串作为键值对，其他请求参数很少
//Uri=BuildUriWithQueryParams（APIRL，reqParams）；
UriBuilder UriBuilder=新的UriBuilder（apiUrl）；
HttpRequestMessage reqMsg=新的HttpRequestMessage（HttpMethod.Post，uriBuilder.Uri）；
HttpMultipartFormDataContent formDataContent=新的HttpMultipartFormDataContent（）；
//文件上传
if（files！=null&&files.Count>0）
{
foreach（存储文件中的存储文件）
{
var inputStream=await-storageFile.OpenAsync（FileAccessMode.Read）；
HttpStreamContent HttpStreamContent=新的HttpStreamContent（inputStream）；
添加（httpStreamContent，“doc”，storageFile.Name）；
}
}
foreach（reqParams中的KeyValuePair KeyValuePair）
添加（新的HttpStringContent（keyValuePair.Value）、keyValuePair.Key）；
reqMsg.Content=formDataContent；
var response=wait HttpClient.SendRequestAsync（reqMsg）；/。AsTask（cts.Token）；

您可以通过标记自己的答案来结束此案例。这对其他人来说是清楚的。