.NET 8 Blazor WASM客户端无法向Web API正确发送数据

我的Web API在Postman和其他两个开发客户端中运行正常，但.NET 8 Blazor WASM和WinForms测试客户端无法正确传递数据。API日志显示请求已到达端点，但textContent字段始终被报告为空（实际已传入有效值）。已确认字段大小写与API的驼峰式参数完全匹配，调试输出的JSON格式正确无拼写错误，但问题依旧。API已上线无法修改。

错误信息：

'textContent' cannot be null or empty

排查后发现API支持multipart表单，Postman和Swagger能生成正确的POST请求格式，推测问题出在请求格式上，需要让HttpClient改用multipart表单发送请求。

API实际期望接收multipart/form-data格式的请求，而非JSON格式。即使JSON结构正确，API无法解析JSON请求体中的字段，因此需要将请求内容改为multipart表单形式。

修改后的Blazor服务代码（TextToAudioService.cs） #

using System;
using System.Net.Http;
using System.Threading.Tasks;

namespace TextToAudioClient.Services
{
    public class TextToAudioService
    {
        private readonly HttpClient _httpClient;

        public TextToAudioService(HttpClient httpClient)
        {
            _httpClient = httpClient;
        }

        public async Task<string> ConvertTextToAudioAsync(string textContent, string outputFileNameNoExt, string audioFormat = "mp3", string voice = "echo", double speed = 0.9)
        {
            try
            {
                var formContent = new MultipartFormDataContent();
                // 表单字段key需与API期望的驼峰式名称完全一致
                formContent.Add(new StringContent(textContent), "textContent");
                formContent.Add(new StringContent(outputFileNameNoExt), "outputFileNameNoExt");
                formContent.Add(new StringContent(audioFormat), "audioFormat");
                formContent.Add(new StringContent(voice), "voice");
                formContent.Add(new StringContent(speed.ToString()), "speed");

                var response = await _httpClient.PostAsync("api/v1/texttoaudio/convertfrombody", formContent);
  
                response.EnsureSuccessStatusCode();

                var audioUrl = await response.Content.ReadAsStringAsync();

                return audioUrl;
            }
            catch (HttpRequestException httpRequestException)
            {
                Console.WriteLine($"HTTP请求错误: {httpRequestException.Message}");
                throw new ApplicationException("处理请求时发生错误。", httpRequestException);
            }
            catch (Exception ex)
            {
                Console.WriteLine($"错误: {ex.Message}");
                throw new ApplicationException("发生意外错误。", ex);
            }
        }
    }
}

修改后的WinForms测试客户端代码 #

using System.Net.Http;

namespace TextToAudioClient;

public partial class Form1 : Form
{
    private readonly HttpClient _httpClient;

    public Form1()
    {
        InitializeComponent();
        _httpClient = new HttpClient();
    }

    private async void btnSendToAPI_Click(object sender, EventArgs e)
    {
        string requestUri = txtAPIroot.Text.Trim() + txtAPIendpointPath.Text.Trim();

        var formContent = new MultipartFormDataContent();
        formContent.Add(new StringContent(txtTextContent.Text.Trim()), "textContent");
        formContent.Add(new StringContent(txtOutputFileNameNoExt.Text.Trim()), "outputFileNameNoExt");
        formContent.Add(new StringContent(txtAudioFormat.Text.Trim()), "audioFormat");
        formContent.Add(new StringContent(txtVoice.Text.Trim()), "voice");
        formContent.Add(new StringContent(txtSpeed.Text.Trim()), "speed");

        try
        {
            var response = await _httpClient.PostAsync(requestUri, formContent);
            response.EnsureSuccessStatusCode();
            var responseBody = await response.Content.ReadAsStringAsync();

            MessageBox.Show("收到响应: " + responseBody, "成功", MessageBoxButtons.OK, MessageBoxIcon.Information);
        }
        catch (HttpRequestException httpRequestException)
        {
            MessageBox.Show("HTTP请求错误: " + httpRequestException.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
        catch (Exception ex)
        {
            MessageBox.Show("发生错误: " + ex.Message, "错误", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }
    }
}

注意事项 #

• 表单字段的key（如textContent）必须与API期望的参数名称完全一致，包括大小写
• 移除了原有的JSON序列化相关代码，因为API不接受JSON格式的请求体
• MultipartFormDataContent会自动设置正确的Content-Type请求头，无需手动指定

内容的提问来源于stack exchange，提问作者MC9000