Xcode playground showing SwiftUI custom button that repeatedly fires an action while touched

RepeatButton.playground

import SwiftUI
import PlaygroundSupport

class Model: ObservableObject {
  @Published var value: Double = 5.0
}

struct RepeatButton: View {
  private let title: String
  private let systemImage: String
  private let interval: TimeInterval
  private let action: () -> Void

  @State private var timer: Timer? = nil

  init(_ title: String, systemImage: String, interval: TimeInterval = 0.4, action: @escaping () -> Void) {
    self.title = title
    self.systemImage = systemImage
    self.interval = interval
    self.action = action
  }

  var body: some View {
    Label(title, systemImage: systemImage)
      .padding(8.0)
      .background(Color.black.brightness(timer != nil ? 0.60 : 0.50))
      .cornerRadius(8.0)
      .gesture(makeGesture())
  }

  private func makeGesture() -> some Gesture {
    DragGesture(minimumDistance: 0)
      .onChanged { _ in
        guard timer == nil else { return }
        timer = Timer.scheduledTimer(withTimeInterval: interval, repeats: true) { _ in action() }
        action()
      }
      .onEnded { _ in
        timer?.invalidate()
        timer = nil
      }
  }
}

struct ContentView: View {
  @ObservedObject var model: Model

  var body: some View {
    VStack {
      VStack(spacing: 8) {
        Text("Value")
        Text(String(format: "%.2f", model.value))
          .font(.title)
      }
      .padding()

      VStack {
        Text("Move slider to modify the model value.")
        Slider(value: $model.value, in: 0...10)
      }
      .padding()
      .border(Color.white)

      VStack {
        Text("Press buttons to step change the model value.")
        HStack {
          RepeatButton("Down", systemImage: "chevron.left", action: decrementAction)
          RepeatButton("Up", systemImage: "chevron.right", action: incrementAction)
        }
        .labelStyle(IconOnlyLabelStyle())
      }
      .padding()
      .border(Color.white)
    }
  }

  private func decrementAction() { changeValue(by: -1.0) }
  private func incrementAction() { changeValue(by:  1.0) }
  private func changeValue(by: Double) { model.value = min(max(model.value + by, 0), 10) }
}

let view = ContentView(model: Model())
PlaygroundPage.current.setLiveView(view)