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C# mvc中没有为此对象定义无参数构造函数

c# asp.net-mvc-4 razor

C# mvc中没有为此对象定义无参数构造函数,c#,asp.net-mvc-4,razor,C#,Asp.net Mvc 4,Razor,当我在视图中使用SelectList时，我得到错误“没有为这个对象定义无参数构造函数”，我看到了很多解决方案，但找不到适合我的解决方案。这是查看代码： @using (Html.BeginForm("Product", "Products", FormMethod.Post, new { @class = "form-horizontal" })) { @Html.ValidationSummary() <div class="form-group"> &

当我在视图中使用SelectList时，我得到错误“没有为这个对象定义无参数构造函数”，我看到了很多解决方案，但找不到适合我的解决方案。这是查看代码：

@using (Html.BeginForm("Product", "Products", FormMethod.Post, new { @class = "form-horizontal" }))
{
   @Html.ValidationSummary()

   <div class="form-group">
       <label class="control-label col-md-3" for="SelectProduct">Select Product</label>
       <div class="col-md-4">
           @Html.DropDownListFor(p => p.SelectProduct, new SelectList(new[] 
           {
             new { Value = "New", Text = "New Entry" },
             new { Value = "Existing", Text = "Existing Entry" },
           }, "Value", "Text"), 
           new { @class = "form-control" })
       </div>
   </div> 
   <div class="form-group">
       <label class="control-label col-md-3" for="productName">Product Name</label>
       <div class="col-md-8">
          @Html.TextBoxFor(u => u.ProductName, new { @class = "form-control", @id = "productName" })
       </div>
   </div>   
}
型号：

public class ProductDto
{
    public ProductDto()
    {
    }
    /// <summary>
    /// Gets or sets whether its New or existing product
    /// </summary>
    public SelectList SelectProduct { get; set; }


    /// <summary>
    /// Gets or sets product name.
    /// </summary>
    public string ProductName { get; set; }

}

公共类产品到
{
公共产品
{
}
/// 
///获取或设置其新产品还是现有产品
/// 
公共选择列表选择产品{get；set；}
/// 
///获取或设置产品名称。
/// 
公共字符串ProductName{get；set；}
}
堆栈跟踪：

[MissingMethodException: No parameterless constructor defined for this  object.]
       System.RuntimeTypeHandle.CreateInstance(RuntimeType type, Boolean publicOnly, Boolean noCheck, Boolean& canBeCached, RuntimeMethodHandleInternal& ctor, Boolean& bNeedSecurityCheck) +0
      System.RuntimeType.CreateInstanceSlow(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark) +119
      System.RuntimeType.CreateInstanceDefaultCtor(Boolean publicOnly, Boolean skipCheckThis, Boolean fillCache, StackCrawlMark& stackMark) +232
     System.Activator.CreateInstance(Type type, Boolean nonPublic) +83
     System.Activator.CreateInstance(Type type) +11
     System.Web.Mvc.DefaultModelBinder.CreateModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Type modelType) +183
    System.Web.Mvc.DefaultModelBinder.BindSimpleModel(ControllerContext controllerContext, ModelBindingContext bindingContext, ValueProviderResult valueProviderResult) +329
     System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +368
     System.Web.Mvc.DefaultModelBinder.GetPropertyValue(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor, IModelBinder propertyBinder) +17
      System.Web.Mvc.DefaultModelBinder.BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, PropertyDescriptor propertyDescriptor) +384
      System.Web.Mvc.DefaultModelBinder.BindProperties(ControllerContext controllerContext, ModelBindingContext bindingContext) +88
                  System.Web.Mvc.DefaultModelBinder.BindComplexElementalModel(ControllerContext controllerContext, ModelBindingContext bindingContext, Object model) +53
         System.Web.Mvc.DefaultModelBinder.BindComplexModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +1314
        System.Web.Mvc.DefaultModelBinder.BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) +416
      System.Web.Mvc.ControllerActionInvoker.GetParameterValue(ControllerContext controllerContext, ParameterDescriptor parameterDescriptor) +317
         System.Web.Mvc.ControllerActionInvoker.GetParameterValues(ControllerContext controllerContext, ActionDescriptor actionDescriptor) +117
       System.Web.Mvc.Async.<>c__DisplayClass25.<BeginInvokeAction>b__1e(AsyncCallback asyncCallback, Object asyncState) +446
       System.Web.Mvc.Async.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout) +130
       System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeAction(ControllerContext controllerContext, String actionName, AsyncCallback callback, Object state) +302
    System.Web.Mvc.<>c__DisplayClass1d.<BeginExecuteCore>b__17(AsyncCallback asyncCallback, Object asyncState) +30
      System.Web.Mvc.Async.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout) +130
  System.Web.Mvc.Controller.BeginExecuteCore(AsyncCallback callback, Object state) +381
       System.Web.Mvc.Async.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout) +130
      System.Web.Mvc.Controller.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state) +317
        System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.BeginExecute(RequestContext requestContext, AsyncCallback callback, Object state) +17
       System.Web.Mvc.<>c__DisplayClass8.<BeginProcessRequest>b__2(AsyncCallback asyncCallback, Object asyncState) +71
   System.Web.Mvc.Async.WrappedAsyncResult`1.Begin(AsyncCallback callback, Object state, Int32 timeout) +130

[MissingMethodException:没有为此对象定义无参数构造函数。]
System.RuntimeTypeHandle.CreateInstance（RuntimeType类型、Boolean publicOnly、Boolean noCheck、Boolean&canBeCached、RuntimeMethodHandleInternal&ctor、Boolean&bNeedSecurityCheck）+0
System.RuntimeType.CreateInstanceSlow（布尔publicOnly、布尔skipCheckThis、布尔fillCache、StackScrawlMark和stackMark）+119
System.RuntimeType.CreateInstanceDefaultCtor（布尔publicOnly、布尔skipCheckThis、布尔fillCache、StackScrawlMark和stackMark）+232
System.Activator.CreateInstance（类型，布尔非公共）+83
System.Activator.CreateInstance（类型）+11
CreateModel（ControllerContext ControllerContext，ModelBindingContext bindingContext，Type modelType）+183
System.Web.Mvc.DefaultModelBinder.BindSimpleModel（ControllerContext ControllerContext，ModelBindingContext bindingContext，ValueProviderResult ValueProviderResult）+329
System.Web.Mvc.DefaultModelBinder.BindModel（ControllerContext ControllerContext，ModelBindingContext bindingContext）+368
System.Web.Mvc.DefaultModelBinder.GetPropertyValue（ControllerContext ControllerContext、ModelBindingContext bindingContext、PropertyDescriptor PropertyDescriptor、IModelBinder propertyBinder）+17
System.Web.Mvc.DefaultModelBinder.BindProperty（ControllerContext ControllerContext，ModelBindingContext bindingContext，PropertyDescriptor PropertyDescriptor）+384
System.Web.Mvc.DefaultModelBinder.BindProperties（ControllerContext ControllerContext，ModelBindingContext bindingContext）+88
System.Web.Mvc.DefaultModelBinder.BindCompleteXelementalModel（ControllerContext ControllerContext，ModelBindingContext bindingContext，Object model）+53
System.Web.Mvc.DefaultModelBinder.BindComplexModel（ControllerContext ControllerContext，ModelBindingContext bindingContext）+1314
System.Web.Mvc.DefaultModelBinder.BindModel（ControllerContext ControllerContext，ModelBindingContext bindingContext）+416
System.Web.Mvc.ControllerActionInvoker.GetParameterValue（ControllerContext ControllerContext，ParameterDescriptor ParameterDescriptor）+317
System.Web.Mvc.ControllerActionInvoker.GetParameterValues（ControllerContext ControllerContext，ActionDescriptor ActionDescriptor）+117
System.Web.Mvc.Async.c__显示类25.b__1e（AsyncCallback AsyncCallback，Object asyncState）+446
System.Web.Mvc.Async.WrappedAsyncResult`1.Begin（异步回调，对象状态，Int32超时）+130
System.Web.Mvc.Async.AsyncControllerActionInvoker.BeginInvokeAction（ControllerContext ControllerContext，String actionName，AsyncCallback回调，对象状态）+302
System.Web.Mvc.c_uuudisplayClassId.b_uuu17（异步回调，异步回调，对象异步状态）+30
System.Web.Mvc.Async.WrappedAsyncResult`1.Begin（异步回调，对象状态，Int32超时）+130
System.Web.Mvc.Controller.BeginExecuteCore（异步回调，对象状态）+381
System.Web.Mvc.Async.WrappedAsyncResult`1.Begin（异步回调，对象状态，Int32超时）+130
System.Web.Mvc.Controller.BeginExecute（RequestContext RequestContext，AsyncCallback回调，对象状态）+317
System.Web.Mvc.Controller.System.Web.Mvc.Async.IAsyncController.BeginExecute（RequestContext RequestContext，AsyncCallback回调，对象状态）+17
System.Web.Mvc.c_uuudisplayClass8.b_uuu2（异步回调，异步回调，对象异步状态）+71
System.Web.Mvc.Async.WrappedAsyncResult`1.Begin（异步回调，对象状态，Int32超时）+130
谢谢

DropDownListFor
用于在您的模型中设置属性值-您的模型包含一个
SelectProduct
属性，该属性的类型为
SelectList
-我猜它应该是
string
类型，因为这是
SelectList
属性的类型视野中的建筑

public class ProductDto
{
    public ProductDto()
    {
    }
    /// <summary>
    /// Gets or sets whether its New or existing product
    /// </summary>
    public string SelectProduct { get; set; }


    /// <summary>
    /// Gets or sets product name.
    /// </summary>
    public string ProductName { get; set; }

  }

公共类产品到
{
公共产品
{
}
/// 
///获取或设置其新产品还是现有产品
/// 
公共字符串SelectProduct{get；set；}
/// 
///获取或设置产品名称。
/// 
公共字符串ProductName{get；set；}
}
请注意，更纯粹的方法是在控制器或视图模型中而不是在视图中构建
SelectList
。这样，您就可以将构建可能值的逻辑从视图本身中分离出来。

如果您在
ProductDto
类中使用的
SelectList
是
System.Web.Mvc.SelectList
，那么这就是问题的原因
System.Web.Mvc.SelectList
没有无参数构造函数

@Html.DropDownListFor(p => p.SelectProduct, new SelectList(new[]
您应该更改此代码

@Html.DropDownListFor(p => p.SelectProductID, new SelectList(new[]
我使用了选择ProductID，因为当您想使用时。它将充满模型

因此，您只能选择dropdownlist中的一项

我希望这对你有用

谢谢。

此代码将帮助您。使用此方法

Htmlcs

@model OspWebsite.Models.bcEvent             
@using (Html.BeginForm())  
@Html.AntiForgeryToken()
  @Html.ValidationSummary(true)
<div class="col-4 ">

    @Html.LabelFor(model => model.eventCountry, new { @class = "col-sm-6  control-label" })   //For Label
    @Html.DropDownList("FeedBack", ViewData["dropdownCountry"] as List<SelectListItem>)     //For DropDown 

 </div>
}
控制器

   public class AdminEventsController : Controller
   {
    [HttpGet]
    public ActionResult addEvent()
    {   
        ////ComboBox Country
        List<SelectListItem> lst = new List<SelectListItem>();
        MngEvent events = new MngEvent();
        DataTable dt1 = events.ShowEvent();
        for (int i = 0; i <= dt1.Rows.Count; i++)
        {
            lst.Add(new SelectListItem { Text = dt1.Rows[i]["ConfrenceCountry"].ToString(), Value = dt1.Rows[i]["ConfrenceID"].ToString() });
        }
        ViewData["dropdownCountry"] = lst;
        return View();
    }
 }

公共类AdminEventsController:控制器
{
[HttpGet]
公共行动结果附录（）
{   
////组合框国家
List lst=新列表（）；
MngEvent事件=新的MngEvent（）；
数据表dt1=事件

public class MngEvent
{
public DataTable ShowEvent()
    {
        try
        {
          SqlConnection con = new SqlConnection(System.Configuration.ConfigurationManager.ConnectionStrings["ospDB"].ConnectionString);

            SqlCommand cmd = new SqlCommand("usp_SelectAllConfrence", con);
            SqlDataAdapter sda = new SqlDataAdapter();
            DataTable dt = new DataTable();
            cmd.CommandType = CommandType.StoredProcedure;
            if (con.State.Equals(ConnectionState.Closed))
                con.Open();
            sda.SelectCommand = cmd;
            sda.Fill(dt);
            con.Close();
            return dt;

        }
        catch (Exception ex)
        {
            throw ex;
        }
    }
  }



   public class AdminEventsController : Controller
   {
    [HttpGet]
    public ActionResult addEvent()
    {   
        ////ComboBox Country
        List<SelectListItem> lst = new List<SelectListItem>();
        MngEvent events = new MngEvent();
        DataTable dt1 = events.ShowEvent();
        for (int i = 0; i <= dt1.Rows.Count; i++)
        {
            lst.Add(new SelectListItem { Text = dt1.Rows[i]["ConfrenceCountry"].ToString(), Value = dt1.Rows[i]["ConfrenceID"].ToString() });
        }
        ViewData["dropdownCountry"] = lst;
        return View();
    }
 }