Subscribe to all ReactiveProperty inside a ObservableList?

[devcube9]

Hi

I haven't been able to find a solution for this problem, but I am encountering this frequent enough that I thought it might be a good idea to ask here:

public class Element {
    public ReactiveProperty<bool> Completed = new();
}

public class List {
    public ObservableList<Element> Elements = new();
    public ReadOnlyReactiveProperty<bool> AllCompleted = ???
}

How do I complete AllCompleted here so that it listens to all Element.Completed in Elements list? The main problem is that Elements list is dynamic and can add/remove elements.

In addition, I stumbled upon this observable to convert CollectionChanged to an observable in UniRx here

Observable.FromEvent<NotifyCollectionChangedEventHandler<Element>, NotifyCollectionChangedEventArgs<Element>>(
                h => (sender, e) => h(e),
                h => source.CollectionChanged += h,
                h => source.CollectionChanged -= h);

but I couldn't get it to work in ObservableCollection because of this error:

The type 'NotifyCollectionChangedEventArgs' may not be a ref struct or a type parameter allowing ref structs in order to use it as parameter 'T' in the generic type or method 'Observable.FromEvent<TDelegate, T>(Func<Action, TDelegate>, Action, Action, CancellationToken)'CS9244