DefaultModelBinder返回子类MVC4

Question

我已经试着读了几天关于这个DefaultModelBinder的文章，但我仍然很困惑。我正在使用MVC 4&EF 5表格层次结构。

我的问题是我有一个资源基类：

  public class Resource : PocoBaseModel
  {
    private int _resourceID;
    private string _title;
    private string _description;
    //public accessors
  }

具有子类（DVD、电子书、书籍等）

public class DVD : Resource
{
    private string _actors;
    //more fields and public accessors
}

我的控制器代码使用自定义ModelBinder

[HttpPost]
public ActionResult Create([ModelBinder(typeof(ResourceModelBinder))] Resource resource)
{
     //controller code
}
public class ResourceModelBinder : DefaultModelBinder
{
  public override object BindModel(ControllerContext controllerContext,
  ModelBindingContext bindingContext)
  {
      var type = controllerContext.HttpContext.Request.Form["DiscriminatorValue"];
      bindingContext.ModelName = type;
      bindingContext.ModelMetadata = ModelMetadataProviders.Current.GetMetadataForType(null, resourceTypeMap[type]);
      return base.BindModel(controllerContext, bindingContext);
    }
static Dictionary<string, Type> resourceTypeMap = new Dictionary<string, Type>
    {
      {"Resource", typeof(Resource)},
      {"Book", typeof(Book)},
      {"DVD", typeof(DVD)},
      {"EBook", typeof(EBook)},
      {"Hardware", typeof(Hardware)},
      {"Software", typeof(Software)}
    };
}

这样我就可以将资源（以DVD、书籍或任何其他类型播放）传递给我的视图

@model Models.Resource
@{
    ViewBag.Title = "Create";
}
<h2>Create</h2>
@using (Html.BeginForm("Create", "Admin", null, FormMethod.Post, null))
{
    @Html.ValidationSummary(true)
    <fieldset>
        <legend>Resource</legend>
        @Html.HiddenFor(model => model.ResourceID)
        @Html.HiddenFor(model => model.ResourceTypeID)
        @Html.HiddenFor(model => model.Committed)
        @Html.Partial("_CreateOrEdit", Model)
        <p>
            <input type="submit" value="Create"/>
        </p>
    </fieldset>
}

并基于其派生属性对其进行绑定，该派生属性发生在局部视图内的开关中。

@using Models.ViewModels;
@using Models.ResourceTypes;
@using Helper;
@model Models.Resource
@Html.HiddenFor(model => Model.DiscriminatorValue);
<table cellspacing="2" cellpadding="2" border="0">
    @{
        string type = Model.DiscriminatorValue;
        switch (type)
        {
            case "Book":
                Book book = (Book)Model;
        <tr>
        <td colspan="2">
            <div class="editor-label" style="padding-top: 15px;">
                @Html.LabelFor(model => model.Title)
            </div>
            <div class="editor-field">
                @Html.TextAreaFor(model => model.Title, new { style = "width: 750px; height: 65px;" })
                @Html.ValidationMessageFor(model => model.Title)
            </div>
        </td>
    </tr>
    <tr>
        <td>
            <div class="editor-label">
                @Html.LabelFor(model => book.Edition)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(model => book.Edition, new { style = "width: 150px;" })
                @Html.ValidationMessageFor(model => book.Edition)
            </div>
        </td>
        <td>
            <div class="editor-label">
                @Html.LabelFor(model => book.Author)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => book.Author)
                @Html.ValidationMessageFor(model => book.Author)
            </div>
        </td>
    </tr>
    <tr>
        <td> 
            <div class="editor-label">
                @Html.LabelFor(model => book.Pages)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(model => book.Pages, new { style = "width: 75px;" })
                @Html.ValidationMessageFor(model => book.Pages)
            </div>
        </td>
    </tr>
      <tr>
        <td colspan="2">
            <div class="editor-label">
                @Html.LabelFor(model => model.Description)
            </div>
            <div class="editor-field">
                @Html.TextAreaFor(model => model.Description, new { style = "width: 750px; height: 105px;" })
                @Html.ValidationMessageFor(model => model.Description)
            </div>
        </td>
    </tr>
     <tr>
        <td colspan="2">
            <div class="editor-label">
                @Html.LabelFor(model => model.AdminNote)
            </div>
            <div class="editor-field">
                @Html.TextAreaFor(model => model.AdminNote, new { style = "width: 750px; height: 105px;" })
                @Html.ValidationMessageFor(model => model.AdminNote)
            </div>
        </td>
    </tr>
    <tr>
        <td>
            <div class="editor-label">
                @{ int copies = Model == null ? 1 : Model.Copies; }
                @Html.LabelFor(model => model.Copies)
            </div>
            <div class="editor-field">
                @Html.TextBoxFor(model => model.Copies, new { style = "width: 75px;", @Value = copies.ToString() })
                @Html.ValidationMessageFor(model => model.Copies)
            </div>
        </td>
    </tr>
    <tr>
        <td>
            <div class="editor-label">
                @Html.LabelFor(model => book.ISBN10)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => book.ISBN10)
                @Html.ValidationMessageFor(model => book.ISBN10)
            </div>
        </td>
        <td>
            <div class="editor-label">
                @Html.LabelFor(model => book.ISBN13)
            </div>
            <div class="editor-field">
                @Html.EditorFor(model => book.ISBN13)
                @Html.ValidationMessageFor(model => book.ISBN13)
            </div>
        </td>
    </tr>
  break;

我的第一个问题是，当我发布回表单时，它作为资源而不是强制类型返回（所以我丢失了所有派生类型属性），这就是我创建ResourceModelBinder的原因。现在它正确地绑定/postbackcast类型，但不绑定资源的基类属性，如Title、ResourceID、ResourceTypeID。。

有人能帮我理解我缺少了什么吗？这样它就能真正绑定基本资源类属性以及派生类型属性。？

Answer 1

所以我所要做的就是在我的自定义ModelBinder类中重写BindProperty方法。

protected override void BindProperty(ControllerContext controllerContext, ModelBindingContext bindingContext, System.ComponentModel.PropertyDescriptor propertyDescriptor)
    {
      if (propertyDescriptor.DisplayName != null)
      {
        var Form = controllerContext.HttpContext.Request.Form;
        string currentPropertyFormValue = string.Empty;
        string formDerivedTypeKey = bindingContext.ModelName.ToLower() + "." + propertyDescriptor.DisplayName;
        string formBaseTypeKey = propertyDescriptor.DisplayName;
        List<string> keywordList = null;
        Type conversionType = propertyDescriptor.PropertyType;
        if (!string.IsNullOrEmpty(Form[formDerivedTypeKey]) || !string.IsNullOrEmpty(Form[formBaseTypeKey]))
        {
          if (!string.IsNullOrEmpty(Form[formDerivedTypeKey]))
          {
            //store current derived type property
            currentPropertyFormValue = Form[formDerivedTypeKey];
          }
          if (!string.IsNullOrEmpty(Form[formBaseTypeKey]))
          {
            //store current base type property
            currentPropertyFormValue = Form[formBaseTypeKey];
          }
        }
        if (conversionType.IsGenericType)
        {
          if (conversionType.GetGenericTypeDefinition() == typeof(List<>))
          {
            if (propertyDescriptor.DisplayName == "KeyWords")
            {
              string[] keywords = currentPropertyFormValue.Split(',');
              if (keywords != null && keywords.Count() > 0)
              {
                //create keyword list
                keywordList = new List<string>();
                foreach (var item in keywords)
                {
                  if (!string.IsNullOrEmpty(item) && !item.Contains(','))
                  {
                    keywordList.Add(item);
                  }
                }
              }
            }
          }
          if (conversionType.GetGenericTypeDefinition() == typeof(Nullable<>))
          {
            // nullable type property.. re-store nullable type to a safe type
            conversionType = Nullable.GetUnderlyingType(conversionType) ?? propertyDescriptor.PropertyType;
          }
        }
        if (!string.IsNullOrEmpty(currentPropertyFormValue))
        {
          //bind property
          if (propertyDescriptor.DisplayName != "KeyWords")
          {
            propertyDescriptor.SetValue(bindingContext.Model, Convert.ChangeType(currentPropertyFormValue, conversionType)); 
          }
          else
            propertyDescriptor.SetValue(bindingContext.Model, Convert.ChangeType(keywordList, conversionType));
        }
      }
      else
        base.BindProperty(controllerContext, bindingContext, propertyDescriptor); //default condition
    }

此方法将遍历可以分配的每个属性。它获取属性的类型，以便您可以将其值从表单转换为适当的类型。可以为null的类型和字符串属性列表存在一些挑战，但它成功绑定，所以我希望这对某些人有用。