How to disable WinForms button if SourceList is empty - dynamic-data

Question

I've been using ReactiveUI with WinForms and just did the switch to DynamicData, using a SourceList instead of a ReactiveBindingList.
As per this issue, WinForms IBindingList Collection Support was added.
I have a listbox which I bind to a list of strings. In order to make it work with WinForms, I've created a BindingList which is connected to the SourceList:
var Images = new SourceList<string>();
var ImagesBindableWinForms = new BindingList<string>();
Images.Connect().Bind(ImagesBindableWinForms).Subscribe();
The BindingList is then bound to the listbox as follows, which works swell:
d(this.Bind(ViewModel, x => x.AdInfo.ImagesBindableWinForms, x => x.listImages.DataSource));
There is a button to remove items form the list. It should be disabled if the list is empty. Before switching to SourceList, this used to work:
ViewModel.DeleteImageCmd = ReactiveCommand.Create(DeleteImage, ViewModel.CanDeleteImage());
public IObservable<bool> CanDeleteImage()
{
var canDeleteImage = this.WhenAnyValue(vm => vm.AdInfo.Images.Count)
.Select(x => x > 0);
return canDeleteImage;
}
The code would enable or disable the button depending on the list count.
The same code no longer works. I guess no event is fired when the count is updated.
How would I go about disabling the button if the SourceList is empty?

Answer 1

It is necessary to create an ObservableCollectionExtended and bind that to the SourceList as well. The CanDeleteImage should use that instead of the SourceList, or the BindingList:
var ImagesBindable = new ObservableCollectionExtended<string>();
Images.Connect().Bind(ImagesBindable).Subscribe();
public IObservable<bool> CanDeleteImage()
{
var canDeleteImage = this.WhenAnyValue(vm => vm.AdInfo.ImagesBindable.Count)
.Select(x => x > 0);
return canDeleteImage;
}
Only disadvantage is that I now have three lists, but it works.