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

25. Timeout and measureInterval

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Previous episode: 24. Debounce and Throttle Next episode: 26. Challenge: Collect Values by Time

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The timeout operator is a special timing operator whose purpose is to semantically distinguish an actual timer from a timeout condition. Therefore, when a timeout operator fires, it either completes the publisher or emits an error you specify. In both cases, the publisher terminates. Let’s look at timeout in a demo.

let subject = PassthroughSubject<Void, Never>()

// 1
let timedOutSubject = subject.timeout(.seconds(5), scheduler: DispatchQueue.main)

let timeline = TimelineView(title: "Button taps")

let view = VStack(spacing: 100) {
  // 1
  Button(action: { subject.send() }) {
    Text("Press me within 5 seconds")
  }
  timeline
}

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

timedOutSubject.displayEvents(in: timeline)

enum TimeoutError: Error {
  case timedOut
}

let subject = PassthroughSubject<Void, TimeoutError>()

let timedOutSubject = subject.timeout(.seconds(5),
                                      scheduler: DispatchQueue.main,
                                      customError: { .timedOut })


let subject = PassthroughSubject<String, Never>()

// 1
let measureSubject = subject.measureInterval(using: DispatchQueue.main)


let subjectTimeline = TimelineView(title: "Emitted values")
let measureTimeline = TimelineView(title: "Measured values")

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

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

subject.displayEvents(in: subjectTimeline)
measureSubject.displayEvents(in: measureTimeline)

let subscription1 = subject.sink {
  print("+\(deltaTime)s: Subject emitted: \($0)")
}

let subscription2 = measureSubject.sink {
  print("+\(deltaTime)s: Measure emitted: \($0)")
}

subject.feed(with: typingHelloWorld)

let subscription2 = measureSubject.sink {
  print("+\(deltaTime)s: Measure emitted: \(Double($0.magnitude) / 1_000_000_000.0)")
}

let measureSubject2 = subject.measureInterval(using: RunLoop.main)

let subscription3 = measureSubject2.sink {
  print("+\(deltaTime)s: Measure2 emitted: \($0)")
}