Somebody earlier sent an answer (deleted) that was inspiring (thanks) even though it didn't work out of the box, maybe due to instantiating a new instance of ViewModelLocator().
It was something like this:
private readonly MainViewModel _mainViewModel = (new ViewModelLocator().Main);
_mainViewModel.ExcuteGridView();
After tweaking, now I have this, and it works:
ViewModelLocator.Main.ExcuteGridView();
In order for this to work though, I had to declare the Main as static inside the ViewModelLocator:
public static MainViewModel Main
{
get
{
return _main;
}
}