In this iteration of iOS Meetup, The experts from Seven Peaks Software will walk you through on the Swift programming language, Giving you the latest tips and tricks for you to be success on the iOS development Saravudh dived deep into RXSwift: Subjects & Operators. RxSwift is a famous library for composing asynchronous and event-based programs by using observable sequences. Subject and Operation are fundamentals of RxSwift. His topic will lead to a better understanding of the mechanism and behavior of subjects and the main combination operators in RxSwift. It is beneficial to begin by learning the fundamentals.

1. RxSwift: Subjects & Operators
Saravudh Sinsomros
30.03.22

2. What is RxSwift
Subjects
○ PublishSubjects
○ BehaviorSubjects
○ ReplaySubjects
○ AsyncSubjects
Combining Operators
○ CombineLatest
○ Merge
○ Zip
Agenda

3. What is RxSwift
RxSwift, simplifies
developing asynchronous
programs by allowing
your code to react to new
data and process it in
sequential, isolated
manner.
raywenderlich.com
Observer 1
Observer 2
Observer 3
Observable<Int>
2, 3, 5, 7, 11, 13, 17 |
2, 3, 5, 7, 11, 13, 17 |
2, 3, 5, 7, 11, 13, 17 |
Operator

4. Subjects

5. PublishSubjects
https://reactivex.io
Starts empty and only
emits new elements to
subscribers

6. Coding
subject.onNext("Green")
let subscriptionTwo = subject
.subscribe(onNext: { item in
print("subscriptionTwo: (item)")
})
subscriptionTwo.disposed(by: disposeBag)
subject.onNext("Blue")
subject.onNext("Red")
subscriptionOne: Red
subscriptionOne: Green
subscriptionOne: Blue
subscriptionTwo: Blue
PublishSubjects
let subscriptionOne = subject
.subscribe(onNext: { item in
print("subscriptionOne: (item)")
})
subscriptionOne.disposed(by: disposeBag)
let subject = PublishSubject<String>()

7. BehaviorSubjects
https://reactivex.io
Starts with an initial
value and replays it or
the latest element to new
subscribers

8. Coding
let subject = BehaviorSubject<String>(value: "Purple")
subject.onNext("Red")
subject.onNext(“Green")
subject.onNext("Blue")
let subscriptionTwo = subject
.subscribe(onNext: { item in
print("subscriptionTwo: (item)")
})
subscriptionTwo.disposed(by: disposeBag)
subscriptionOne: Purple
subscriptionOne: Red
subscriptionOne: Green
subscriptionTwo: Green
subscriptionOne: Blue
subscriptionTwo: Blue
BehaviorSubjects
let subscriptionOne = subject
.subscribe(onNext: { item in
print("subscriptionOne: (item)n")
})
subscriptionOne.disposed(by: disposeBag)

9. ReplaySubjects
https://reactivex.io
Initialized with a buffer
size and will maintain a
buffer of elements up to
that size and replay it to
new subscribers

10. Coding
let subject = ReplaySubject<String>.create(bufferSize: 3)
subject.onNext("Red")
subject.onNext("Green")
let subscriptionTwo = subject
.subscribe(onNext: { item in
print("subscriptionTwo: (item)n")
})
subscriptionTwo.disposed(by: disposeBag)
subject.onNext("Blue")
subscriptionOne: Red
subscriptionOne: Green
subscriptionTwo: Red
subscriptionTwo: Green
subscriptionOne: Blue
subscriptionTwo: Blue
ReplaySubjects
let subscriptionOne = subject
.subscribe(onNext: { item in
print("subscriptionOne: (item)n")
})
subscriptionOne.disposed(by: disposeBag)

11. AsyncSubjects
https://reactivex.io
Emits only the last value

12. Coding
let subject = AsyncSubject<String>()
subject.onNext("Red")
let subscriptionTwo = subject
.subscribe(onNext: { item in
print("subscriptionTwo: (item)n")
})
subscriptionTwo.disposed(by: disposeBag)
subject.onNext("Green")
subject.onNext("Blue")
subject.onCompleted()
subscriptionOne: Blue
subscriptionTwo: Blue
AsyncSubjects
let subscriptionOne = subject
.subscribe(onNext: { item in
print("subscriptionOne: (item)n")
})
subscriptionOne.disposed(by: disposeBag)

13. Combining Operators

14. Merge
combine multiple
Observables into one by
merging their emissions
https://reactivex.io

15. Coding
let input1 = PublishSubject<String>()
let input2 = PublishSubject<String>()
let output = Observable.of(input1.asObservable(),
input2.asObservable()).merge()
output.subscribe(onNext: { item in
print("(item)n")
}).disposed(by: disposeBag)
input1.onNext("20")
input1.onNext("40")
input1.onNext("60")
input2.onNext("1")
input1.onNext("80")
input1.onNext("100")
input2.onNext("1")
20
40
60
1
80
100
1
Merge

16. CombineLatest
combine values from
several sequences
together
https://reactivex.io

17. Coding
let input1 = PublishSubject<String>()
let input2 = PublishSubject<String>()
let output = Observable.combineLatest(input1, input2, resultSelector: {
lastTop, lastBottom in
"((lastTop)(lastBottom))"
})
output.subscribe(onNext: { item in
print("combineLatest: (item)n")
}).disposed(by: disposeBag)
input1.onNext("1")
input2.onNext("A")
input1.onNext("2")
input2.onNext("B")
input2.onNext("C")
input2.onNext("D")
input1.onNext("3")
input1.onNext("4")
(1A)
(2A)
(2B)
(2C)
(2D)
(3D)
(4D)
CombineLatest

18. Zip
combine the emissions
of multiple Observables
together via a specified
function and emit single
items for each
combination based on
the results of this
function
https://reactivex.io

19. Coding
let input1 = PublishSubject<String>()
let input2 = PublishSubject<String>()
let output = Observable.zip(input1.asObservable(), input2.asObservable())
output.subscribe(onNext: { item1, item2 in
print("(item1)(item2)n")
}).disposed(by: disposeBag)
input1.onNext("1")
input2.onNext("A")
input1.onNext("2")
input2.onNext("B")
input2.onNext("C")
input2.onNext("D")
input1.onNext("3")
input1.onNext("4")
input1.onCompleted()
input2.onNext("E")
1A
2B
3C
4D
Zip

20. Discussion

21. “First, solve the problem.
Then, write the code.”
- John Johnson

22. UPCOMING MEETUP
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