POST上的MVC4通用集合模型问题

Question

I'm trying to implement a basic Questionnaire engine that utilizes the Questionnaire model as below:

public class Questionnaire
{
    public ICollection<Step> Steps { get; set; }
}

public class Step
{
    ICollection<IQuestion> Questions { get; set; }
}

public class TextBoxQuestion : IQuestion
{
    public QuestionTypeEnum QuestionType { get; set; }
    public string QuestionText { get; set; }
}

public class DropDownQuestion : IQuestion
{
    public QuestionTypeEnum QuestionType { get; set; }
    public string QuestionText { get; set; }
    public IList<string> Options { get; set; }
}

QuestionEditor Template:

@model IList<Models.IQuestion>

@for (int i = 0; i < @Model.Count(); i++)
{
    @Html.EditorFor(x => x[i], @Model[i].QuestionType.ToString());

}

TextBoxQuestion Editor:

public class TextBoxQuestion : IQuestion
    {
        public QuestionTypeEnum QuestionType { get; set; }
        public string QuestionText { get; set; }
    }

DropDownQuestion Editor:

public class DropDownQuestion : IQuestion
    {
        public QuestionTypeEnum QuestionType { get; set; }
        public string QuestionText { get; set; }
    }

Roughly following Jon Egerton's example here I'm implementing a generic ICollection of IQuestion interface. MVC interprets each IQuestion by it's type and renders either the TextBoxQuestion or DropDownQuestion editor template accordingly. Great.

However when the Questionnaire model is post back to the Controller the IQuestion collections are all null.

Can anyone help me with advice on whether there is a better approach or whether I can hook up a DependencyResolver or something else so that MVC can interpret my IQuestion objects back as TextBoxQuestion and DropDownQuestion types?

Hope this explanation is clear, feel free to ask any questions.

thanks all in advance

Mark

Answer 1

Found a resolution for this if anyone is trying to achieve the same.

This article on MSDN Magazine was extremely useful.

It explains some key concepts I didn't understand such as Model Binding is recursive so the processing traverses the entire object graph and applies a Model Binder for each Type.

The work through on the General Purpose Abstract Model Binder was the solution I used along with the custom AbstractModelBinderProvider.

Hope this helps someone

Mark