ViewData property in ViewResult is Null

[aaron-hammond]

HI,

I'm having a little trouble with returning a ViewResult from an orchestrator.

Where in previous versions of MVC we've done this:

    return new ViewResult
    {
        ViewName = "Index",
        ViewData = {Model = _formViewModelBuilder.BuildModel()}
    };

In MVC 6 this throws a null reference exception. Setting the model property of the ViewData is invalid as the value of ViewData is null? I believe this has something to do with dependency injection but i can't find a concrete explanation anywhere as to why this behavior is happening.

The simplest way i can get this to work is something like:

       return new ViewResult
        {
            ViewName = "Index",
            ViewData = new ViewDataDictionary<FormViewModel>(ViewData, model)
        };

This uses the Microsoft.AspNet.Mvc.Controller.ViewData property. I can pass this property through to the orchestrator but i'm not sure if this is just plain wrong and i'm missing a trick here?

Any help would be appreciated.

Thanks

[dougbu]

ViewResult is much simpler in MVC 6 than MVC 5. Only the methods have behaviour now. And unfortunately for this particular case, it's no longer possible to create a ViewDataDictionary instance without a IModelMetadataProvider implementation or another ViewDataDictionary instance.

What is your general scenario? Why not set ViewData.Model and create a ViewResult instance as in Controller.View()?

            // Do not override ViewData.Model unless passed a non-null value.
            if (model != null)
            {
                ViewData.Model = model;
            }

            return new ViewResult()
            {
                ViewName = viewName,
                ViewData = ViewData,
                TempData = TempData
            };

[aaron-hammond]

@dougbu Thanks for the response.

In our applications i try to keep a consistent approach with the architecture, we use an orchestrator pattern to keep the controllers as lightweight as possible:

Consider:

 public class FormController 
 {
    private readonly IFormOrchestrator _orchestrator;

    public FormController(IFormOrchestrator orchestrator)
    {
        _orchestrator = orchestrator;
    }

    public IActionResult Index()
    {
        return _orchestrator.GetIndexResult();
    }
}



 public class FormOrchestrator : IFormOrchestrator 
 {
    public IActionResult GetIndexResult()
    {            
        var model = _formViewModelBuilder.BuildModel();

        return new ViewResult
        {
            ViewName = "Index",
            ViewData = // here is where we would have created the viewdata.
        };
    }
 }

Based on the new implementation i'm assuming the best way to achieve what i want is to pass the viewdata property from the controller to the orchestrator as follows?

 public class FormController 
 {
    ...
    public IActionResult Index()
    {
        return _orchestrator.GetIndexResult(ViewData);
    }
 }



public class FormOrchestrator : IFormOrchestrator 
{
    public IActionResult GetIndexResult(ViewDataDictionary viewData)
    {            
        var model = _formViewModelBuilder.BuildModel();

        return new ViewResult
        {
            ViewName = "Index",
            ViewData = new ViewDataDictionary<ApplicantFormViewModel>(viewData, model);
        };
    }
 }

Thanks for your help in advance.

[dougbu]

Your code looks fine.

Side note: Initializing ViewResult.TempData using the FormController.TempData value may also be required for some scenarios.

[aaron-hammond]

brilliant, thanks for the help on this again, really appreciate it.