Register the same view twice to TabControl with different behavior

Question

I search for a smart way to instantiate one View and ViewModel multiple times in a Tabcontrol with slightly different behavior. In best case by using Prism7.1

My current solution is;

in my MainView

        <TabControl
            ItemsSource="{Binding TabItemCollection}"
            SelectedItem="{Binding SelectedTabItem}"
            ItemContainerStyle="{DynamicResource ItemSize20_HeaderBinding}" 
            mah:TabControlHelper.Underlined="SelectedTabItem">
            <TabControl.Resources>
                <DataTemplate DataType="{x:Type vm:MaskingCreationViewModel}" >
                    <local:MaskingCreation/>
                </DataTemplate>
            </TabControl.Resources>
        </TabControl>

in my MainViewModel

    public class MainViewModel
    {
        public ObservableCollection<MaskingCreationViewModel> TabItemCollection { get; set; }
        public MaskingCreationViewModel SelectedTabItem { get; set; }

        public MainViewModel()
        {
            TabItemCollection = new ObservableCollection<MaskingCreationViewModel>();
            TabItemCollection.Add(new MaskingCreationViewModel(new TabBehaviorA()));
            TabItemCollection.Add(new MaskingCreationViewModel(new TabBehaviorB()));

            SelectedTabItem = TabItemCollection[0];
        }
    }

Here I want to inject the "TabBehavior" in my ViewModel provide the different behavior. I tried that already with Prism to register the "MaskingCreation" in the TabControl via Region, but with that I get two problems.

If I normal register the View with the region a don't have the chance to inject the behavior I want.

            regionManager.RegisterViewWithRegion(Regions.Masking, typeof(MaskingCreation));

if I use this I have a problem with every line of this.
- I want to get a new Instance from the ServiceLocation with exact this variation of TabBehavior, but I don't know how this should work.
- Becaus I don't get this Consturctor injection to work I have to provide a property for the TabBehavior class.
- And the last and worst thing. I have to store a reference of the View in my ViewModel. I want to avoid using of the DataContext inside my ViewModel.

            regionManager.RegisterViewWithRegion(Regions.Masking, () => 
            {
                var vm = ServiceLocator.Current.GetInstance<MaskingCreationViewModel>();
                vm.Behavior = new TabBehaviorB();
                return vm.GetView();
            });

Did anybody know a smart solution that fits in the MVVM pattern?

`I want to get a new Instance from the ServiceLocation` - you better have a very good reason to want this, can you explain a bit? — Haukinger, Feb 16 '19 at 09:47
Because I was thinking about a scenario with a more complex class with more dependencies. Then it could be very ugly to instantiate it. And is this not one of the benefits of using an IoC-Container? To remove some big Constructor calls from the program logic? — Garleck, Feb 16 '19 at 11:26
No, the IoC-Container is about managing the dependencies, that is, creating instances if required, keeping singletons around and so on. If you have classes with lots of dependencies _and_ need to create them on the fly (as opposed to have them injected into the constructor), employ a factory for them. I summarised this once here: https://stackoverflow.com/questions/39768318/how-better-to-resolve-dependencies-in-object-created-by-factory/39788267#39788267 — Haukinger, Feb 16 '19 at 11:30
Ok, I understand your explanation. Then is my current solution at the Top not so far away from yours. The only open point is there maybe a smarter way to do this with the Region concept of prism. — Garleck, Feb 16 '19 at 12:06

score 0 · Accepted Answer · answered Feb 16 '19 at 12:19

In the view model, I'd inject a factory for MaskingCreationViewModel and all the tab behaviors:

internal class MainViewModel : BindableBase
{
    public MainViewModel( IMaskingCreationViewModelFactory maskingCreationViewModelFactory, IEnumerable<ITabBehavior> tabBehaviors )
    {
        foreach (var tabBehavior in tabBehaviors)
            TabItemCollection.Add( maskingCreationViewModelFactory.Create( tabBehavior ) );

        SelectedTabItem = TabItemCollection.FirstOrDefault();
    }

    public ObservableCollection<MaskingCreationViewModel> TabItemCollection { get; } = new ObservableCollection<MaskingCreationViewModel>();
    public MaskingCreationViewModel SelectedTabItem { get => _selectedTabItem; set => SetProperty( ref _selectedTabItem, value ); }

    private MaskingCreationViewModel _selectedTabItem;
}

Register the same view twice to TabControl with different behavior

1 Answers1