In RxCocoa/RxSwift, how to observe BehaviorRelay<[object]> array size changed

Question

I'd like to subscribe to a BehaviorRelay<[object]>, and I'd like to execute some functions whenever we append or remove elements.

I've used the distinctUntilChange method

BehaviorRelay<[object]>.asObservable().distinctUntilChanged{ $0.count != $1.count}.subscribe{....}

But didn't work. What should I try? Should I try using other Subjects or Relays to achieve this purpose?

var objects = BehaviorRelay<[Object]>(value: [])
let disposeBag = DisposeBag()

objects.asObservable()
.subscribe(onNext: { (objects) in
//Do something only when appending or removing elements.
}).disposed(by: disposeBag)

//For example
let tempObj = objects.value

tempObj.append(newObj)
objects.accept(tempObj)//this will be called

tempObj.removeAll()
objects.accept(tempObj)//this will be called

tempObj.property = "Change Property"
objects.accept(tempObj)//this will NOT be called

Answer 1

From documentation:

• parameter comparer: Equality comparer for computed key values.

I believe you should check the Equality with == operator. So, in your case, try this way:

BehaviorRelay<[object]>
    .asObservable()
    .distinctUntilChanged{ $0.count == $1.count}
    .subscribe{....}