CODEWITHSUNDEEP
c#wpfmvvmmvvm-light
WSC
WSC

Reputation: 993

Using MvvmLight.Messaging.Messenger to instantiate new View + ViewModel (Window)

I have my MainView and an associated MainViewViewModel which are linked by ViewModelLocator.

Within MainViewViewModel there is a command which should trigger a new Window to open which has it's own View and ViewModel (NewView and NewViewViewModel).

In a lot of the examples I've seen it is suggested to use Mvvmlight's Messenger to do something like this:

public class MainViewViewModel
{

    private void OpenNewWindow()
    {
        Messenger.Default.Send(new NotificationMessage("NewView"));
    }

}

And then register the NewViewViewModel and handle the message like this:

public class NewViewViewModel
{
   public NewViewViewModel()
   {
       Messenger.Default.Register<NotificationMessage>(this, NotificationMessageReceived);
   }

    private void NotificationMessageReceived(NotificationMessage obj)
    {
         if (obj.Notification == "NewView")
         {
             NewView view = new NewView();
             view.Show();
         }
    }
}

However, this doesn't work because the NewViewViewModel isn't yet instantiated (so isn't registered with Messenger). Additionally, this doesn't fit with MVVM because NewViewViewModel is responsible for creating NewView.

What is the correct way to achieve a simple command which instantiates and opens a new View and ViewModel pair which are linked via ViewModelLocator and setting of DataContext="{Binding NewView, Source={StaticResource Locator}}" in NewView.xml?

Upvotes: 0

Views: 251

Answers (1)

mm8
mm8

Reputation: 169150

Use a window service:

MVVM show new window from VM when seperated projects

You may either inject the view model to with an IWindowService implementation or use a static WindowService class:

public static class WindowService
{
    public static void OpenWindow()
    {
        NewView view = new NewView();
        view.Show();
    }
}

Dependency injection is obviously preferable for being able to unit test the view model(s) and switch implementations of IWindowService at runtime.

Upvotes: 3

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