为什么这段代码会给我Request.Form无效的内容类型？（ASP.NET Core）

Question

这是使用RazorPages的ASP.NET Core 2.0 OnGet方法。

cs文件：

using System;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace CoreRazor2.Pages
{
  public class IndexModel : PageModel
  {
    [BindProperty]
    public int result { get; set; }
    public void OnGet(string operationType)
    {
      string result;
      switch (operationType)
      {
        case "+":
          result = Request.Form["First"];
          break;
        case "-":
          result = "1";
          break;
        case "/":
          result = "2";
          break;
        case "*":
          result = "3";
          break;
      }

    }
  }
}

cshtml文件：

@page
@model IndexModel
@{
    ViewData["Title"] = "Calculator";
}

<form method="GET">
<label>First Value: </label>
<input name="First"/>
<br/>
<br/>
<label>Second Value: </label>
<input name="second"/>
<br/>
<br/>
<input type="submit" name="operationType" value="+"/>
<input type="submit" name="operationType" value="-"/>
<input type="submit" name="operationType" value="*"/>
<input type="submit" name="operationType" value="/"/>
</form>
@Model.result

在第一个表单输入中输入值并单击“ +”提交按钮时，程序将在Request.Form [“ First”]处引发以下异常：

Exception has occurred: CLR/System.InvalidOperationException
An exception of type 'System.InvalidOperationException' occurred in Microsoft.AspNetCore.Http.dll but was not handled in user code: 'Incorrect Content-Type: '
   at Microsoft.AspNetCore.Http.Features.FormFeature.ReadForm()
   at Microsoft.AspNetCore.Http.Internal.DefaultHttpRequest.get_Form()
   at CoreRazor2.Pages.IndexModel.OnGet(String operationType) in c:\Users\Administrator\Desktop\CoreRazor2\Pages\Index.cshtml.cs:line 17
   at Microsoft.AspNetCore.Mvc.RazorPages.Internal.ExecutorFactory.VoidHandlerMethod.Execute(Object receiver, Object[] arguments)
   at Microsoft.AspNetCore.Mvc.RazorPages.Internal.PageActionInvoker.<InvokeHandlerMethodAsync>d__29.MoveNext()

有谁知道为什么或可以指出一些有用的文档吗？

Answer 1

出于通用目的（作为日志记录），当您需要处理所有类型的 HttpRequests 时，请使用HttpRequest.HasFormContentType

示例代码：

if (request.HasFormContentType && request.Form != null && request.Form.Count() > 0)
{
            dynamic form = new { };
            foreach (var f in request.Form)
                form[f.Key] = f.Value;
            d.form = form;
}

Answer 2

基于GET的表单通过URL而不是表单传递值。您需要使用Request.Query["First"]。Request.Form仅在发布表单时有效。但是，由于您使用的是Razor页面，因此您可以省去所有麻烦，而只需使用模型绑定即可：

using System;
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.RazorPages;

namespace CoreRazor2.Pages
{
    public class IndexModel : PageModel
    {
        public int Result { get; set; }

        public void OnGet(string operationType, int first, int second)
        {
            switch (operationType)
            {
                case "+":
                    Result = first + second;
                    break;
                case "-":
                    Result = first - second;
                    break;
                case "/":
                    Result = first / second;
                    break;
                case "*":
                    Result = first * second;
                    break;
            }

        }
    }
}