Question

In my Shell window I have a workspace region to allow view switching via RequestNavigate. I’m using Unity with a View-First approach such that the view initialization look like:

public partial class WelcomeView : UserControl
{
    public WelcomeView(WelcomeViewModel vm)
    {
        InitializeComponent();
        this.DataContext = vm;
    }
}

When the application loads, I want to navigate to a default view so my BootStrappers InitializeShell looks as follows:

protected override void InitializeShell()
{
    Application.Current.MainWindow = (Window)Shell;
    Application.Current.MainWindow.Show();

    var regionManager = ServiceLocator.Current.GetInstance<IRegionManager>();
    regionManager.RequestNavigate("MainWorkspaceRegion", "WelcomeView");
}

Now, my default view, WelcomeView, requires a WelcomeViewModel to be injected in the constructor, and in turn, the WelcomeViewModel requires some service to be injected in its constructor:

public class WelcomeViewModel : INotifyPropertyChanged
{
    public WelcomeViewModel(ISomeService someService)
    {
         // Use some service
         someService.SomeEventOccured += new Action(someService_SomeEventOccured);
    }

    ...
}

The problem is when ISomeService is supplied by a module, since the module is not initialized at the time InitializeShell is called, WelcomeViewModel cannot be constructed and in turn neither can WelcomeView.

Whats the proper way to do this?

Answer 1

The proper way to do this is to use a module dependency

So the module that has dependencies will contain

[ModuleDependency("SomeModule")] 
[ModuleDependency("SomeOtherModule")] 
public class MyModule : IModule { } 

And the module on which it is dependent will contain:

[Module(ModuleName = "SomeModule")] 
public class MyOtherModule: IModule 

it also makes sense not to use “magic strings”, as I have here and, instead have a static class in your common/infrastructure project that contains the names of all your modules.

This will allow prism to load the modules in the correct order so that your dependencies always resolve.