Reactive Programming in iOS with Combine

Feb 4 2021 · Swift 5.3, macOS 11.0, Xcode 12.2

Part 4: Timing, Scheduling and Sequencing Operators

24. Debounce and Throttle

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Previous episode: 23. Delay and Collect Next episode: 25. Timeout and measureInterval

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When designing user interfaces you want to update some views when a user enters data in a text field. However, you don’t want to respond to every single keystroke the user makes. You want some mechanism to wait until the user stops typing. This is where debounce comes into play. Let’s look at debounce in a demo.

// 1
let subject = PassthroughSubject<String, Never>()

// 2
let debounced = subject
  .debounce(for: .seconds(1.0), scheduler: DispatchQueue.main)
  // 3
  .share()

let subjectTimeline = TimelineView(title: "Emitted values")
let debouncedTimeline = TimelineView(title: "Debounced values")

let view = VStack(spacing: 100) {
	subjectTimeline
	debouncedTimeline
}

PlaygroundPage.current.liveView = UIHostingController(rootView: view)

subject.displayEvents(in: subjectTimeline)
debounced.displayEvents(in: debouncedTimeline)

let subscription1 = subject
  .sink { string in
    print("+\(deltaTime)s: Subject emitted: \(string)")
  }

let subscription2 = debounced
  .sink { string in
    print("+\(deltaTime)s: Debounced emitted: \(string)")
  }

subject.feed(with: typingHelloWorld)


let throttleDelay = 1.0

// 1
let subject = PassthroughSubject<String, Never>()

// 2
let throttled = subject
  .throttle(for: .seconds(throttleDelay), scheduler: DispatchQueue.main, latest: false)
  // 3
  .share()

let subjectTimeline = TimelineView(title: "Emitted values")
let throttledTimeline = TimelineView(title: "Throttled values")

let view = VStack(spacing: 100) {
  subjectTimeline
  throttledTimeline
}

PlaygroundPage.current.liveView = UIHostingController(rootView: view)

subject.displayEvents(in: subjectTimeline)
throttled.displayEvents(in: throttledTimeline)

let subscription1 = subject
  .sink { string in
    print("+\(deltaTime)s: Subject emitted: \(string)")
  }

let subscription2 = throttled
  .sink { string in
    print("+\(deltaTime)s: Throttled emitted: \(string)")
  }

subject.feed(with: typingHelloWorld)

let throttled = subject
  .throttle(for: .seconds(throttleDelay), scheduler: DispatchQueue.main, latest: true)
  .share()