RxSwift how to append to BehaviorSubject<[]>

Question

Since Variable is deprecated in RxSwift 4, what is the equivalent way for BehaviorSubject to do the following?

let observable = Variable<[Int]>([])
observable.value.append(1)

Answer 1

BehaviorRelay is a replacement for Variable in newer versions RxSwift, which seem to work similarly. Variable has a property value which emits event when changed. Similar to that with BehaviorRelay, you can use underlying accept(:), method to change the value.

let array = BehaviorRelay(value: [1, 2, 3])

array.subscribe(onNext: { value in
    print(value)
}).disposed(by: disposeBag)


// for changing the value, simply get current value and append new value to it
array.accept(array.value + [4])

Nevertheless, this can be worked on with BeviourSubject as well if you wish to,

let subject = BehaviorSubject(value: [10, 20])
subject.asObserver().subscribe(onNext: { value in
    print(value)
}).disposed(by: disposeBag)

You can get latest value from BehaviorSubject with a throwing function value(), and so appending the value with look like this,

do {
    try subject.onNext(subject.value() + [40]) // concatenating older value with new 
} catch {
    print(error)
}

Notice that you would need to call onNext to pass new value to BehaviorSubject which is not as simple as it is with Variable or BahaviorRelay

Answer 2

We can also use BehaviorRelay extension to append objects easily:

extension BehaviorRelay where Element: RangeReplaceableCollection {

    func add(element: Element.Element) {
        var array = self.value
        array.append(element)
        self.accept(array)
    }
}

Usage:

self.wishList.add(element: item.element)

wishList is object of BehaviorRelay