Question

How do I require that all of the objects in a parameter array be passed as out? In my following code, I know that it’s failing because my original parameters never get assigned and are thus null. Even though I would think they’d be passed as reference without having to explicitly say so, they don’t seem to be. As a result, I’ve had to try and pass all of it as an out parameter.

Here’s the parts of my code that I think matter.

ChatController(some elements removed)

class ChatController : ControllerBase
{
    #region Views

    ChatAreaView viewChatArea;
    UserListView viewUserArea;
    MessageView viewMessageArea;
    LoginPromptView viewLoginPrompt;

    #endregion

    #region ViewModels

    ChatAreaViewModel viewModelChatArea;
    UserAreaViewModel viewModelUserArea;
    MessageAreaViewModel viewModelMessageArea;
    LoginPromptViewModel viewModelLoginPrompt;

    #endregion
    public override void CreateViewsAndViewModels()
    {
        //InitializeViewAndViewModel(out viewChatArea, out viewModelChatArea);
        //InitializeViewAndViewModel(out viewMessageArea, out viewModelMessageArea);
        //InitializeViewAndViewModel(out viewUserArea, out viewModelUserArea);
        //InitializeViewAndViewModel(out viewLoginPrompt, out viewModelLoginPrompt);

        InitializeViewsAndViewModels(new FrameworkElement[] { viewChatArea, viewUserArea, viewMessageArea, viewLoginPrompt },
                                     new object[] { viewModelChatArea, viewModelUserArea, viewModelMessageArea, viewModelLoginPrompt });
    }
}

ControllerBase(some elements removed)

public abstract class ControllerBase : PrismBase
{
    public void InitializeViewAndViewModel<TView, TViewModel>(out TView view, out TViewModel viewModel)
        where TView : FrameworkElement, new()
        where TViewModel : new()
    {
        view = new TView();
        viewModel = new TViewModel();

        view.DataContext = viewModel;
    }

    public void InitializeViewsAndViewModels(FrameworkElement[] views, object[] viewModels)
    {
        if (views.Length != viewModels.Length)
            throw new ArgumentOutOfRangeException("views and viewModels must have the same number of elements.");

        for (int i = 0; i < views.Length -1 ; i++)
            InitializeViewAndViewModel(out views[i], out viewModels[i]);
    }
}

The problem area is here

public void InitializeViewsAndViewModels(FrameworkElement[] views, object[] viewModels)
{
}

All these objects here that I pass in to the method remain null when the method returns.

InitializeViewsAndViewModels(new FrameworkElement[] { viewChatArea, viewUserArea, viewMessageArea, viewLoginPrompt },
                             new object[] { viewModelChatArea, viewModelUserArea, viewModelMessageArea, viewModelLoginPrompt });

I want to require passing all of the views and viewModels array objects as out, but I can only seem to require the entire array itself be passed as out.

What can I do here?

EDIT: The entire problem seems to stem from the Plural form of the method, as I described above. If I got rid of that and I simply did this…

public override void CreateViewsAndViewModels()
{
    InitializeViewAndViewModel(out viewChatArea, out viewModelChatArea);
    InitializeViewAndViewModel(out viewMessageArea, out viewModelMessageArea);
    InitializeViewAndViewModel(out viewUserArea, out viewModelUserArea);
    InitializeViewAndViewModel(out viewLoginPrompt, out viewModelLoginPrompt);

    //InitializeViewsAndViewModels(new FrameworkElement[] { viewChatArea, viewUserArea, viewMessageArea, viewLoginPrompt },
    //                             new object[] { viewModelChatArea, viewModelUserArea, viewModelMessageArea, viewModelLoginPrompt });
}

everything works just swimmingly.

Answer 1

You can’t have arrays of out values in C#.

Now what you are trying to do is very strange and even if arrays of out would be supported you will still endup with trobles – you are loosing types of variable in you arrays, so there is no reasoanble way to new them up correctly.

Your current generic methods have multiple implementations in derived classes – one per pair of types (i.e. your ChatController have what you can view as 4 distinct implementation of InitializeViewAndViewModel each for specific pair of views). Your newly proposed code would have to find that missing type information somehow…