ASP.Net Core 3.1：控制器方法总是从 HttpPost 调用接收 NULL 参数

Question

我使用 ASP.Net Core 3.1 和 MVC 模式创建了一个全新的 Visual Studio 2019 Web 应用程序。

我的控制器有一个 HttpPost 方法，它应该有一个传入的 Json 对象（我使用 [FromBody] 作为传入参数）。

无论我尝试什么，传入的参数始终为 Null。 我尝试将参数更改为字符串，并将模型修改为简单的 3 字段类，但它仍然以空值形式出现。

我使用 Chrome 的开发人员工具来确保我的页面从 JavaScript Post 回调正确发送 Json 对象（并且还使用 Postman 执行相同的操作）并得到相同的结果：我的参数仍然为 Null。

我需要做什么才能让参数作为实际值出现？

我的控制器：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Threading.Tasks;
using Microsoft.AspNetCore.Mvc;
using Newtonsoft.Json;

using canvasApiLib.API;
using CanvasGrades.Models.AuxiliaryModels;

namespace CanvasGrades.Controllers
{
    public class FinalGradeController : Controller
    {

        public async Task<IActionResult> Index()
        {
            // Course Name
            dynamic courseDetails = await clsCoursesApi.getCourseDetails(accessToken, apiUrl, canvasCourseId);
            ViewData["CourseName"] = courseDetails.name;

            // Course Term
            dynamic courseTerm = await clsEnrollmentTermsApi.getEnrollmentTerm(accessToken, apiUrl, canvasAccountID, termNum);
            ViewData["CourseTerm"] = courseTerm.name;

            return View();
        }

        [HttpPost]
        public async Task<IActionResult> LoadTable([FromBody]DTParameters dtParameters)
        {
            //DTParameters dtParameters = new DTParameters();

            if (dtParameters == null)
            {
                dtParameters = new DTParameters();
            }
        }
    }
}

我的 DTParameters 模型：

public class DTParameters
{
    public int Draw { get; set; }
    public DTColumn[] Columns { get; set; }
    public DTOrder[] Order { get; set; }
    public int Start { get; set; }
    public int Length { get; set; }
    public DTSearch Search { get; set; }
    public IEnumerable<string> AdditionalValues { get; set; }
}

我看到的大多数示例都说明在 Startup.cs 文件的配置调用中调整 app.UseMVC 实例化，但我的没有：

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services.AddDistributedMemoryCache();
    services.AddControllersWithViews();
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    else
    {
        app.UseExceptionHandler("/Home/Error");
        // The default HSTS value is 30 days. You may want to change this for production scenarios, see https://aka.ms/aspnetcore-hsts.
        app.UseHsts();
    }

    app.UseHttpsRedirection();
    app.UseStaticFiles();

    app.UseRouting();

    app.UseAuthorization();

    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllerRoute(
            name: "default",
            pattern: "{controller=Home}/{action=Index}/{id?}");
    });
}

（添加）

{"draw":1,"columns":[{"data":"studentName","name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":"studentEMail","name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":null,"name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":"finalGrade","name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":"lastAttendDate","name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":null,"name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":null,"name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":"bannerID","name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}},{"data":"crn","name":"","searchable":true,"orderable":true,"search":{"value":"","regex":false}}],"order":[{"column":0,"dir":"asc"}],"start":0,"length":10,"search":{"value":"","regex":false}}

我再次重试了我的简单参数，注意到我发送的原始 ID 字段是一个整数，但是当我将它设为字符串（如模型所述）时，它没有问题。

public class SimpleParam
{
    public string Id { get; set; }
    public string Name { get; set; }
    public string Foo { get; set; }
}

{"id": "1", "name": "fred", "foo": "bob"}

所以，这意味着我将不得不弄清楚我的 DTParameters 模型有什么问题。

Answer 1

错误是“dir”：“asc”。 您需要将其更改为 int ("dir": 0)，或者用

[JsonConverter(typeof(JsonStringEnumConverter))]

或者把它放在 startup.cs

public void ConfigureServices(IServiceCollection services)
{

    services
        .AddControllers()
        .AddJsonOptions(options => 
           options.JsonSerializerOptions.Converters.Add(new JsonStringEnumConverter())
        );

    //...
 }

您的输入美化了：

{
    "draw": 1,
    "columns": [
        {
            "data": "studentName",
            "name": "",
            "searchable": true,
            "orderable": true,
            "search": {
                "value": "",
                "regex": false
            }
        }
    ],
    "order": [
        {
            "column": 0,
            "dir": "asc"
        }
    ],
    "start": 0,
    "length": 10,
    "search": {
        "value": "",
        "regex": false
    }
}

您的 Datatables 类具有正确的装饰（见上文 DTOrderDir）：

public class DTParameters
{
    public int Draw { get; set; }
    public DTColumn[] Columns { get; set; }
    public DTOrder[] Order { get; set; }
    public int Start { get; set; }
    public int Length { get; set; }
    public DTSearch Search { get; set; }
    public IEnumerable<string> AdditionalValues { get; set; }
}

public class DTColumn
{
    public string Data { get; set; }
    public string Name { get; set; }
    public bool Searchable { get; set; }
    public bool Orderable { get; set; }
    public DTSearch Search { get; set; }
}

public class DTOrder
{
    public int Column { get; set; }
    public DTOrderDir Dir { get; set; }
}

[JsonConverter(typeof(JsonStringEnumConverter))]
public enum DTOrderDir
{
    ASC,
    DESC
}

public class DTSearch
{
    public string Value { get; set; }
    public bool Regex { get; set; }
}

阅读此处了解更多信息： JavaScriptSerializer - 枚举作为字符串的 JSON 序列化