SelectedObjects from PropertyGrid should subscribe to INotifyCollectionChanged

[KokeBlacksmith]

On binding a collection to DataContext of the property grid, It only get updated on changing the property value, but not on collection changes like Clear, Add, Remove, etc..

So the ViewModel PropertyGridViewModel.cs could check if the new value is a INotifyCollectionChanged and subscribe to changes as follows:

public object SelectedObject
{
    get => _SelectedObject;
    set 
    { 
        if(_SelectedObjects is INotifyCollectionChanged oldNotifyCollection)
        {
            oldNotifyCollection.CollectionChanged -= OnSelectedObjectsCollectionChanged;
        }

        this.RaiseAndSetIfChanged(ref _SelectedObject, value);

        if(_SelectedObjects is INotifyCollectionChanged newNotifyCollection)
        {
            newNotifyCollection.CollectionChanged += OnSelectedObjectsCollectionChanged;
        }
    }
}

private void OnSelectedObjectsCollectionChanged(object sender, NotifyCollectionChangedEventArgs args)
{
    RaisePropertyChanged(new PropertyChangedEventArgs(nameof(SelectedObject)));
}

This way, changes on a collection will be shown in the property grid as well.