Question

I’m trying to create an application similar to Visual Studio in that we have a main content area (i.e. where documents are displayed in a TabControl, not a true MDI interface), with a menu on the side.

So far, I have everything working, except the content. My goal is that when a user double clicks on an item in the navigation menu on the side, it opens the document in the Content region. This works, but every time I double click it spawns a new instance of that same view. There’s a chance that I could have multiple views of the same type (but different “names”) in the TabControl content container.

Right now, my code looks something like this…

            IRegion contentRegion = IRegionManager.Regions[RegionNames.ContentRegion];

            object view = IUnityContainer.Resolve(viewModel.ViewType, viewModel.UniqueName);

            if (!IUnityContainer.IsRegistered(viewModel.ViewType, viewModel.UniqueName))
            {
                IUnityContainer.RegisterInstance(viewModel.UniqueName, view);
                contentRegion.Add(view);
            }

            contentRegion.Activate(view);

However, it appears that the view is never registered, even though I register it… I imagine I’m probably doing this wrong — is there another way to do this? (re: the right way)

Answer 1

So, the problem was trying to do it this entire way. The smart method (for anyone else trying to do this) is to make use of Prism the correct way.

What I ended up doing was instead Navigating by:

1. In the Navigation Menu, constructing a UriQuery (included in Prism) with the UniqueID of the view I want to display (which is guaranteed to be unique) and adding that to the View I wanted to navigate to, i.e.:

    IRegionManager.RequestNavigate(RegionNames.ContentRegion, new Uri(ViewNames.MyViewName + query.ToString(), UriKind.Relative));

where query is the UriQuery object.

2. Register the View and ViewName in the Module via:

        IUnityContainer container = ServiceLocator.Current.GetInstance<IUnityContainer>();
        container.RegisterType<object, MyView>(Infrastructure.ViewNames.MyViewName);

3. In the View, make sure the ViewModel is a parameter on the constructor. Let Prism inject this manually for us. Inside the constructor, make sure you set the DataContext to the incoming ViewModel.

4. Finally, make sure your ViewModel implements INavigationAware interface… This is a very simple implementation of it (UniqueID is a property on the ViewModel):

    public virtual bool IsNavigationTarget(NavigationContext navigationContext)
    {
        if (navigationContext.Parameters != null)
            return (navigationContext.Parameters["UniqueID"] == UniqueID);

        return false;
    }

    public virtual void OnNavigatedFrom(NavigationContext navigationContext)
    {
    }

    public virtual void OnNavigatedTo(NavigationContext navigationContext)
    {
        if (navigationContext.Parameters != null)
            UniqueID = navigationContext.Parameters["UniqueID"];
    }

From here, Prism will ensure that only one view of your “UniqueID” will exists, while allowing for others of the same view, but different ViewModel (or data for that ViewModel, i.e. viewing two users in different tabs, but both use the same templated view).