System.MissingMethodException:没有为此对象定义无参数构造函数 [英] System.MissingMethodException: No parameterless constructor defined for this object

问题描述

我正在使用带有 Html.ListBoxFor 的 MVC 2.0，如下所示:

I'm using MVC 2.0 with a Html.ListBoxFor as below:

<% using (Html.BeginForm()) { %>

       <input type="submit" value=">" />

        <%= Html.ListBoxFor(x => x.lstTest, new MultiSelectList(new [] {"someone", "crap", "why"})) %>

    <% } %>

当我单击下面的输入提交按钮而未选择任何内容时，它会很好地回发，当我选择列表框中的 3 个项目之一时，它会引发此错误:

When I click the input submit button below with nothing selected, it posts back fine, when I select one of the 3 items in the listbox it throws this error:

 System.MissingMethodException: No parameterless constructor defined for this object.

有什么想法吗?这是我的控制器代码:

Any ideas? here is my controller code:

 [HandleError]
public class HomeController : Controller
{
    public HomeController()
    {

    }

    public ActionResult Index()
    {
        ViewData["Message"] = "Test Harness";

        return View();
    }

    [HttpGet]
    public ActionResult About()
    {
        ViewData["mykey"] = "Test Harness";

        LogOnModel model = new LogOnModel();
        model.lstTest = new MultiSelectList(new [] {"A", "B", "C"});

        return View(model);
    }


    [HttpPost]
    public ActionResult About(LogOnModel model)
    {
        ViewData["mykey"] = "Test Harness";

        model.lstTest = new MultiSelectList(new [] { "" });

        return View(model);
    }
}

推荐答案

你的 LogOnModel 有无参数构造函数吗?它需要一个 DefaultModelBinder 来实例化它.此外，当您发布异常时，请发布异常对象的完整堆栈跟踪，否则我们只是在猜测错误实际发生的位置.

Does your LogOnModel have a parameterless constructor? It needs one for the DefaultModelBinder to instantiate it. Additionally, when you post the exception, please post the full stack trace from the exception object, else we're simply guessing where the error actually took place.

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