ASP.NET MVC 2 - Html.DropDownListFor与视图模型混乱 [英] ASP.NET MVC 2 - Html.DropDownListFor confusion with ViewModel

问题描述

我得到完全失去了和困惑就如何使用新的强类型Html.DropDownListFor帮手在ASP.NET MVC 2.0 R2

在查看我书面方式：

 ＆LT;％= Html.DropDownListFor（M = GT; m.ParentCategory，新的SelectList（Model.Categories，类别ID，姓名，Model.ParentCategory），[无]）％＆GT;＆所述;％= Html.ValidationMessageFor（M =＆GT; m.ParentCategory）％GT;
 

和我的模型对象是这样的：

 公共类CategoryForm：FormModelBase
{
    公共CategoryForm（）
    {
        分类=新的List＆LT;类别及GT;（）;        Categories.Add（新CategoryForm.Category（）{
                           类别ID = 1，
                           NAME =处理器}）;
        Categories.Add（新CategoryForm.Category（）{
                           类别ID = 2，
                           NAME =内存}）;
        Categories.Add（新CategoryForm.Category（）{
                           类别ID = 3，
                           NAME =硬盘驱动器}）;
    }    // ...等道具，略... //    公共范畴ParentCategory {搞定;组; }    公众的IList＆LT;类别及GT;分类{搞定;保护套; }    公共类目录
    {
        公众诠释？ {类​​别ID获取;组; }
        公共字符串名称{;组; }
    }
}
 

问题是，当我从下拉列表中的项目，说的第一个项目，我得到以下ValidationMessageFor错误的值1是无效的。

于是我改变视图...

 ＆LT;％= Html.DropDownListFor（M =方式＆gt; m.ParentCategory ** **的CategoryId，
                              新的SelectList ... / SNIP）％GT;
 

现在它的工作原理，有点。在我的ViewModel的ParentCategory属性设置了正确的类别ID'，但'名称'为NULL。我是不是最好只具有ParentCategory财产，而不是一个强类型的类别的对象一个可空INT？

解决方案

我也遇到同样的问题。

当我调试的行动，并期待在ModelState.Values​​ [1] .Errors [0] .Exception例如，我看到以下内容：

{参数转换，从类型'System.String'输入'System.Collections.Generic.KeyValuePair`2 [System.String，mscorlib程序，版本= 2.0.0.0，文化=中性公钥= b77a5c561934e089] [System.Int64，mscorlib程序，版本= 2.0.0.0，文化=中性公钥= b77a5c561934e089]]'失败，因为没有类型转换器可以将这些类型之间的转换。} {System.Exception的System.InvalidOperationException}

在我的方案，是从字典中创建我的SelectList和我用这个在我看来：

 ＆LT;％= Html.DropDownListFor（X =＆GT; x.MyDictionary，
                             新的SelectList（
                                 Model.MyDictionary，
                                 值，
                                 键））％GT;
 

当我把它改为：

 ＆LT;％= Html.DropDownListFor（X =＆GT; x.MyDictionary.Keys，//＆LT;  - 改变。键
                             新的SelectList（
                                 Model.MyDictionary，
                                 值，
                                 键））％GT;
 

这工作没有问题。

感谢您。

I'm getting totally lost and confused on how to use the new strongly typed Html.DropDownListFor helper on ASP.NET MVC 2.0 R2

In the View I'm writting:

<%= Html.DropDownListFor(m => m.ParentCategory, new SelectList(Model.Categories, "CategoryId", "Name", Model.ParentCategory), "[ None ]")%>

<%= Html.ValidationMessageFor(m => m.ParentCategory)%>

and my Model object is thus:

public class CategoryForm : FormModelBase
{
    public CategoryForm()
    {
        Categories = new List<Category>();

        Categories.Add(new CategoryForm.Category() {
                           CategoryId = 1, 
                           Name = "CPUs" });
        Categories.Add(new CategoryForm.Category() { 
                           CategoryId = 2, 
                           Name = "Memory" });
        Categories.Add(new CategoryForm.Category() { 
                           CategoryId = 3, 
                           Name = "Hard drives" });
    }

    // ...other props, snip... //

    public Category ParentCategory { get; set; }

    public IList<Category> Categories { get; protected set; }

    public class Category
    {
        public int? CategoryId { get; set; }
        public string Name { get; set; }
    }
}

The problem is that when I select an item from the dropdown list, say the first item, I get the following ValidationMessageFor error "The value '1' is invalid."

So I change the View to...

<%= Html.DropDownListFor(m => m.ParentCategory.**CategoryId**, 
                              new SelectList .../ snip  ) %>

Now it works, kinda. The ParentCategory property in my ViewModel is set with the correct 'CategoryId' but the 'Name' is NULL. Am I better off just having a nullable int for ParentCategory property instead of a strongly typed 'Category' object?

解决方案

I was also experiencing the same issue.

When I debug the Action and look at the ModelState.Values[1].Errors[0].Exception for example, I see the following:

{"The parameter conversion from type 'System.String' to type 'System.Collections.Generic.KeyValuePair`2[[System.String, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089],[System.Int64, mscorlib, Version=2.0.0.0, Culture=neutral, PublicKeyToken=b77a5c561934e089]]' failed because no type converter can convert between these types."} System.Exception {System.InvalidOperationException}

In my scenario, my SelectList is created from a Dictionary and i use this in my view:

<%=Html.DropDownListFor(x => x.MyDictionary, 
                             new SelectList(
                                 Model.MyDictionary, 
                                 "Value", 
                                 "Key")) %>

When I changed it to:

<%=Html.DropDownListFor(x => x.MyDictionary.Keys, // <-- changed to .Keys
                             new SelectList(
                                 Model.MyDictionary, 
                                 "Value", 
                                 "Key")) %>

It worked without issues.

Thank you.

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