MVVM Navigation | Buttons inside of View

Question

Hello stack overflow community, I'm new to MVVM and have worked on a couple of tutorials to get some of the basics working (bindings, RelayCommand etc..). A single window Application works so far pretty good, but now I need to add a Login and one or two other "views". I was not expecting this to be that painful.... :D

After working on a tutorial from (Github), I could figure out, if I place a button/command from the MainWindow.xaml for example to /view/Home.xaml the command still fires, the CurrentView also updates but the MainWindow doesn't update/show? So.... I'm very confused on what is going on, hopefully someone has a logical explanation.

After looking into a couple more examples on stack overflow, I was reading about MVVM light and messaging, is this the way to make things work? If so, could someone please show a simple example. not sure if a simple example exists..

Thank you very much, Anything is helpful

Alex

PS: I have updated my Navigation Test Repository github.com that shows exactly the issue. Hope there is an easy solution to this :D

UPDATE:

I have updated my code and came to the conclusion that I need to use either MVVM-light messaging or Prism Event Aggregator.

I decided to give Prism Event Aggregator a shot and have "tried" to implement the Interface and added the aggregator inside of my constructor in both view models, but now my whole solution doesn't work anymore. What am I doing wrong here?

NavigationViewModel.cs

public class NavigationViewModel : ViewModelBase
{
    private IEventAggregator _eventAggregator;

    public NavigationViewModel(IEventAggregator eventAggregator)
    {
        LoginCommand = new RelayCommand(Login);
        PwResetCommand = new RelayCommand(PwReset);
        LogoutCommand = new RelayCommand(Logout);


        // Startup Page
        CurrentView = new LoginViewModel();

        //Prism Event Aggregator
        _eventAggregator = eventAggregator;

        eventAggregator
        .GetEvent<MyEvent>()
        .Publish(true);
    }

    public class MyEvent : PubSubEvent<bool>
    {  
    }

WorkOrderViewModel.cs

    public class WorkOrderViewModel : ViewModelBase
{
    private IEventAggregator _eventAggregator;

    public WorkOrderViewModel(IEventAggregator eventAggregator)
    {
        // Prism Event Aggregator
        _eventAggregator = eventAggregator;

        eventAggregator
        .GetEvent<NavigationViewModel.MyEvent>()
        .Subscribe(OnIsSavedEvent);
    }

    public void OnIsSavedEvent(bool isSaved)
    {
        bool IsModified = !isSaved;
    }
}

NavigationView.xaml.cs:

public partial class NavigationView : UserControl
{
    public NavigationView()
    {
        InitializeComponent(); // <-- System.NullReferenceException: 'Object reference not set to an instance of an object.'
    }
}

Answer 1

I solved this by implementing MS Toolkit Messages, it was way simpler as I thought it would be.