Question

My understanding is that ASP.NET MVC only allows you to POST objects to Actions in the Controller, where the Action’s arguments accept the posted object as a Concrete class.

Is there any way around this, or a good alternative?

In my case, I have an action which accepts an interface as an argument:

public ActionResult SaveAdjustment(IModel model)
{
    switch (model.SubsetType)
    {
        // factory like usage
    }
}

And for this action, I have numerous views, all strongly typed to objects that implement IModel, all which I want to be able to post to this one method.

Of course, running this give me the error:

Cannot create an instance of an interface

Is there a nice work around to this? Or do I need to create an Action method for each and send them over to a method like this?

Answer 1

Although I mentioned this as a possible solution in my original question, its the solution I have gone with in the end and I actually quite like it now. This way I didn’t need to touch the model default binding implementation and I think this approach is a more readable/understandable approach than what I was originally asking for.

In case its not clear why I wanted to go for this approach, I have added an example of how I can use this for its OO benifits.

    [HttpPost]
    public ActionResult SaveModelA(ModelA model)
    {
        return SaveModel(model);
    }

    [HttpPost]
    public ActionResult SaveModelB(ModelB model)
    {
        return SaveModel(model);
    }

    private ActionResult SaveModel(IModel model)
    {
        IExampleService exampleService;
        IRequirements requirements;

        switch (model.SubsetType)
        {
            case SubsetType.ModelA:
                myService = new ModelAService();
                requirements = new ModelARequirements
                {
                    ModelASpecificProperty = "example"
                };
                break;
            case SubsetType.ModelB:
                myService = new ModelBService();
                requirements = new ModelBRequirements
                {
                    ModelBSpecificProperty1 = "example",
                    ModelBSpecificProperty2 = "example2",
                    ModelBSpecificProperty3 = "example3"
                };
                break;                
            default:
                throw new InvalidEnumArgumentException();
        }

        var serviceResonse = exampleService.ExecuteExample(model, requirements);

        return RedirectToAction("Index", new
        {
            ExampleData = serviceResponse.ExampleDate
        });
    }

In case it isn’t clear in the code:

ModelA : IModel
ModelB : IModel
ModelARequirements : IModelRequirements
ModelBRequirements : IModelRequirements
ModelAService : IExampleService
ModelBService : IExampleService

// and IModel defines a property SubsetType SubsetType { get; }