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我正在使用 ASP.NET MVC 2 Beta。我可以使用 Steven Sanderson 的技术（在他的《Pro ASP.NET MVC 框架》一书中）创建一个类似工作流的向导，除了使用 Session 而不是隐藏的表单字段来跨请求保存数据。当我的模型不是集合时，我可以在页面之间来回切换并维护 TextBox 中的值而不会出现任何问题。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; }
}

但是当我传递一个 IEnumerable 时，我无法让它工作。在我看来，我正在尝试遍历模型并为列表中的每个人生成名称和电子邮件的文本框。我可以很好地生成表单，我可以使用我的值提交表单并转到第 2 步。但是，当我在 Step2 中单击 Back 按钮时，它会将我带回 Step1，并带有一个空表单。我之前填充的字段都不存在。一定有什么我错过了。有人可以帮帮我吗？

这是我的观点：

<% 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);
    }
}
4

1 回答 1

1

据我所知，ASP.NET MVC 2 Beta 不支持此功能，ASP.NET MVC 2 RC 也不支持此功能。我挖掘了 MVC 源代码，它看起来支持字典，但不支持 IEnumerable<>（或包含嵌套 IEnumerable 对象）的模型，它是 IList<> 之类的继承者。

问题出在 ViewDataDictionary 类中。特别是，GetPropertyValue 方法仅提供一种从字典属性（通过调用 GetIndexedPropertyValue）或简单属性中检索属性值的方法，方法是使用 PropertyDescriptor.GetValue 方法提取值。

为了解决这个问题，我创建了一个 GetCollectionPropertyValue 方法来处理作为集合的模型（甚至是包含嵌套集合的模型）。我在这里粘贴代码以供参考。注意：我对优雅没有任何要求——事实上，所有的字符串解析都很丑陋，但它似乎正在工作。这是方法：

// 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;
        }

这是调用新方法的修改后的 GetPropertyValue 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
            };
        }

同样，这是在 ASP.NET MVC 2 RC 的 ViewDataDictionary.cs 文件中。我应该在 MVC codeplex 站点上创建一个新问题来跟踪这个问题吗？

于 2009-12-21T10:29:06.393 回答