ASP.NET MVC：如何维护国家的TextBox当你的视图模型是一家集/列表/ IEnumerable的

Question

我使用ASP.NET MVC 2贝塔。但是使用而不是隐藏的表单字段会话保持跨请求的数据，我可以创建一个使用史蒂芬·桑德森的技术像工作流程向导（在他的书临ASP.NET MVC框架）。我可以去来回页之间，并在TextBox保持值没有任何问题，当我的模型不是一个集合。一个例子是一个简单的Person模型：

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Email { get; set; }
}

但我无法得到这个，当我绕过一个IEnumerable工作。在我看来，我试图通过示范运行，并为姓名和电子邮件文本框列表中的每个人。我可以生成的形式很好，我可以用我的价值观提交表单，然后转到步骤2。但是，当我点击第二步后退按钮，它把我带回到第一步一个空的形式。我以前填充字段均存在。一定有什么东西我失踪。有人可以帮我吗？

下面是我的看法：

<% using (Html.BeginForm()) { %>
<% int index = 0;
   foreach (var person in Model) { %>
       <fieldset>
            <%= Html.Hidden("persons.index", index.ToString())%>
            <div>Name: <%= Html.TextBox("persons[" + index.ToString() + "].Name")%></div>
            <div>Email: <%= Html.TextBox("persons[" + index.ToString() + "].Email")%></div>
       </fieldset>
       <% index++;
   } %>  
   <p><input type="submit" name="btnNext" value="Next >>" /></p>
<% } %>

这是我的控制器：

public class PersonListController : Controller
{
    public IEnumerable<Person> persons;

    protected override void OnActionExecuting(ActionExecutingContext filterContext)
    {
        persons = (Session["persons"]
            ?? TempData["persons"]
            ?? new List<Person>()) as List<Person>;
        // I've tried this with and without the prefix.
        TryUpdateModel(persons, "persons"); 
    }

    protected override void OnResultExecuted(ResultExecutedContext filterContext)
    {
        Session["persons"] = persons;

        if (filterContext.Result is RedirectToRouteResult)
            TempData["persons"] = persons;
    }

    public ActionResult Step1(string btnBack, string btnNext)
    {
        if (btnNext != null)
            return RedirectToAction("Step2");

        // Setup some fake data
        var personsList = new List<Person> 
            { 
                new Person { Name = "Jared", Email = "test@email.com", },
                new Person { Name = "John", Email = "test2@email.com" } 
            };

        // Populate the model with fake data the first time
        // the action method is called only. This is to simulate
        // pulling some data in from a DB.
        if (persons == null || persons.Count() == 0)
            persons = personsList;

        return View(persons);
    }

    // Step2 is just a page that provides a back button to Step1
    public ActionResult Step2(string btnBack, string btnNext)
    {
        if (btnBack != null)
            return RedirectToAction("Step1");

        return View(persons);
    }
}

Answer 1

据我所知，这是不是在ASP.NET MVC 2 Beta版的支持，也不是在ASP.NET MVC 2 RC的支持。我通过MVC源代码，挖它看起来是的IEnumerable <>（或包含嵌套的IEnumerable对象）像字典，但不支持模型，它的传承人喜欢的IList <>。

的问题是在的ViewDataDictionary类。特别地，GetPropertyValue方法仅提供了一种方法（通过调用GetIndexedPropertyValue）使用PropertyDescriptor.GetValue方法拉出值或简单的属性来检索词典属性的属性值。

要解决这个问题，我创建的处理是集合（甚至包含嵌套集合模型）模型下的GetCollectionPropertyValue方法。我在这里粘贴代码，以供参考。注：我没有做出任何的优雅索赔 - 事实上所有的字符串解析是很丑陋，但它似乎是工作。下面是该方法：

// Can be used to pull out values from Models with collections and nested collections.
        // E.g. Persons[0].Phones[3].AreaCode
        private static ViewDataInfo GetCollectionPropertyValue(object indexableObject, string key)
        {
            Type enumerableType = TypeHelpers.ExtractGenericInterface(indexableObject.GetType(), typeof(IEnumerable<>));
            if (enumerableType != null)
            {
                IList listOfModelElements = (IList)indexableObject;

                int firstOpenBracketPosition = key.IndexOf('[');
                int firstCloseBracketPosition = key.IndexOf(']');

                string firstIndexString = key.Substring(firstOpenBracketPosition + 1, firstCloseBracketPosition - firstOpenBracketPosition - 1);
                int firstIndex = 0;
                bool canParse = int.TryParse(firstIndexString, out firstIndex);

                object element = null;
                // if the index was numeric we should be able to grab the element from the list
                if (canParse)
                    element = listOfModelElements[firstIndex];

                if (element != null)
                {
                    int firstDotPosition = key.IndexOf('.');
                    int nextOpenBracketPosition = key.IndexOf('[', firstCloseBracketPosition);

                    PropertyDescriptor descriptor = TypeDescriptor.GetProperties(element).Find(key.Substring(firstDotPosition + 1), true);

                    // If the Model has nested collections, we need to keep digging recursively
                    if (nextOpenBracketPosition >= 0)
                    {
                        string nextObjectName = key.Substring(firstDotPosition+1, nextOpenBracketPosition-firstDotPosition-1);
                        string nextKey = key.Substring(firstDotPosition + 1);

                        PropertyInfo property = element.GetType().GetProperty(nextObjectName);
                        object nestedCollection = property.GetValue(element,null);
                        // Recursively pull out the nested value
                        return GetCollectionPropertyValue(nestedCollection, nextKey);
                    }
                    else
                    {
                        return new ViewDataInfo(() => descriptor.GetValue(element))
                        {
                            Container = indexableObject,
                            PropertyDescriptor = descriptor
                        };
                    }
                }
            }

            return null;
        }

这里是改性GetPropertyValue方法，该方法调用新方法：

private static ViewDataInfo GetPropertyValue(object container, string propertyName) {
            // This method handles one "segment" of a complex property expression

            // First, we try to evaluate the property based on its indexer
            ViewDataInfo value = GetIndexedPropertyValue(container, propertyName);
            if (value != null) {
                return value;
            }

            // If the indexer didn't return anything useful, continue...

            // If the container is a ViewDataDictionary then treat its Model property
            // as the container instead of the ViewDataDictionary itself.
            ViewDataDictionary vdd = container as ViewDataDictionary;
            if (vdd != null) {
                container = vdd.Model;
            }

            // Second, we try to evaluate the property based on the assumption
            // that it is a collection of some sort (e.g. IList<>, IEnumerable<>)
            value = GetCollectionPropertyValue(container, propertyName);
            if (value != null)
            {
                return value;
            }

            // If the container is null, we're out of options
            if (container == null) {
                return null;
            }

            // Third, we try to use PropertyDescriptors and treat the expression as a property name
            PropertyDescriptor descriptor = TypeDescriptor.GetProperties(container).Find(propertyName, true);


            if (descriptor == null) {
                return null;
            }

            return new ViewDataInfo(() => descriptor.GetValue(container)) {
                Container = container,
                PropertyDescriptor = descriptor
            };
        }

再次，这是在ASP.NET MVC 2 RC的ViewDataDictionary.cs文件。我应该创建一个新的问题跟踪此对MVC的CodePlex网站？