在MVC4中使用@Html.Hidden的空引用剃鬚刀

Question

我有兩個視圖創建&編輯。 兩者都有一個叫做ModelType的隱藏字段，可以在我的模型聯編程序中使用它來綁定所有的子類。

此隱藏字段在編輯視圖中正常工作，但在創建視圖中無法正常工作。 我得到一個null reference exception在行：

@Html.Hidden("ModelType" , Model.GetType().AssemblyQualifiedName) 

在創建視圖。

請幫助這裏出了什麼問題。

Edit.cshtml

@using PartyBiz.Models.Objects 
@model Organization 

@using (Html.BeginForm("Edit", "Organization", FormMethod.Post)) 
{ 
@Html.ValidationSummary(true) 
<fieldset> 
    <legend>Edit Organization</legend> 
    <div class="editor-label"> 
     @Html.LabelFor(model => model.C) 
     @Html.TextBoxFor(model => model.C, new { @class = "txt"}) 
     @Html.ValidationMessageFor(model => model.C) 
    </div> <br /> 

    <div class="editor-label"> 
     @Html.LabelFor(model => model.N) 
     @Html.TextBoxFor(model => model.N, new { @class = "txt"}) 
     @Html.ValidationMessageFor(model => model.N) 
    </div> <br /> 
    <div class="editor-label"> 
     @Html.LabelFor(model => model.D) 
     @Html.TextBoxFor(model => model.D, new { @class = "txt"}) 
     @Html.ValidationMessageFor(model => model.D) 
    </div> 
    <br /> 
     @Html.HiddenFor(model=> model.PID) 
     @Html.Hidden("ModelType" , Model.GetType().AssemblyQualifiedName) 
     <input type="submit" value="Edit" /> 

</fieldset> 
} 

Create.cshtml

@using PartyBiz.Models.Objects 
@model Organization 

@using (Html.BeginForm("Create", "Organization", FormMethod.Post)) 
{ 

@Html.ValidationSummary(true) 
<fieldset> 
    <legend>Create a New Organization</legend> 

    <div class="editor-label"> 
     @Html.LabelFor(model => model.C) 
     @Html.TextBoxFor(model => model.C, new { @class = "txt"}) 
     @Html.ValidationMessageFor(model => model.C) 
    </div> <br /> 

    <div class="editor-label"> 
     @Html.LabelFor(model => model.N) 
     @Html.TextBoxFor(model => model.N, new { @class = "txt"}) 
     @Html.ValidationMessageFor(model => model.N) 
    </div> <br /> 

    <div class="editor-label"> 
     @Html.LabelFor(model => model.D) 
     @Html.TextBoxFor(model => model.D, new { @class = "txt"}) 
     @Html.ValidationMessageFor(model => model.D) 
    </div> 
    <br /> 
     <input type="submit" value="Create" /> 
     @Html.Hidden("ModelType" , Model.GetType().AssemblyQualifiedName) 

</fieldset> 
} 

模型綁定

public override object BindModel(ControllerContext controllerContext, ModelBindingContext bindingContext) 
    { 
     if (bindingContext.ValueProvider.ContainsPrefix("ModelType")) 
     { 
      //get the model type 
      var typeName = (string)bindingContext 
       .ValueProvider 
       .GetValue("ModelType") 
       .ConvertTo(typeof(string)); 
      var modelType = Type.GetType(typeName); 

      //tell the binder to use it 
      bindingContext.ModelMetadata = 
       ModelMetadataProviders 
       .Current 
       .GetMetadataForType(null, modelType); 
     } 
     return base.BindModel(controllerContext, bindingContext); 
    } 

Answer 1

我的猜測是，你不傳遞任何值作爲Create模型方法。你創建方法可能是這樣的：

public ActionResult Create() 
{ 
    return View(); 
} 

這將導致Model財產是在剃刀模板null。要解決此問題，您可以傳入模型類的默認實例：

public ActionResult Create() 
{ 
    return View(new Organization()); 
}