Observe ObservableCollection after adding element and add to CanExecute from ReactiveCommand

[Tenjim]

Hi guys,

I want to observe an ObservableCollection when we adding Elements. This condition will be use into the CanExecute from a ReactiveCommand :

For example :

private ObservableCollection<Person> _selectedPerson;

public ObservableCollection<Person> SelectedPerson
{
    get => _selectedPerson;
    set => _selectedPerson = value;
}

public PersonPanelViewModel()
{

TestButton.Command = ReactiveCommand.Create(() =>
                {
                    //Doing something
                }, this.WhenAnyValue( y =>y.SelectedPerson,
                           selection.Where(d => d.IsSelected).Select(d => d.LastName).Distinct().Count() ==
                           selection.Where(d => d.IsSelected).Select(d => d.LastName).Count())

            );

}
        

My issue here came from my SelectedPerson collection is set null collection at first.

Can we observe this collection when the collection changes because I want to do the WhenAnyValue when I have added something into it ?

Thanks in advance.

[Tenjim]

Hi guys,

I have try to use dynamicdata from docs and this similar discussions (link discussion) with that example :

public bool canExecute { get; set; }

SelectedPerson
               .ToObservableChangeSet(x => x)
               .ToCollection()
               .Select(x =>
                   x.Any(x => x.IsSelected) && 
                   x.Where(d => d.IsSelected).Select(d => d.LastName).Distinct().Count() ==
                   x.Where(d => d.IsSelected).Select(d => d.LastName).Count()))
               .ToProperty(this, x => x.canExecute );

TestButton.Command = ReactiveCommand.Create(() =>
               {
                   //Doing something
               }, this.WhenAnyValue( y =>y.canExecute )

Not working for me. Do I have done some mistake from using it ?