A iOS flashlight like button in SwiftUI.

LongPressButton.swift

//
//  LongPressButton.swift
//  Pachino
//
//  Created by Frad LEE on 6/28/21.
//

import SwiftUI

// MARK: - LongPressButton

/// A iOS flashlight like button.
///
/// # References
///
/// - [Building Fluid Interfaces. How to create natural gestures and…](https://medium.com/@nathangitter/building-fluid-interfaces-ios-swift-9732bb934bf5)
/// - [Composing SwiftUI Gestures](https://developer.apple.com/documentation/swiftui/composing-swiftui-gestures)
struct LongPressButton<Label: View>: View {
  // MARK: Lifecycle

  public init(@ViewBuilder label: () -> Label, action: @escaping () -> Void) {
    self.action = action
    self.label = label()
  }

  // MARK: Internal

  @State var viewState: Bool = false

  var action: () -> Void
  var label: Label

  // var alertMessage: String
  // var alertDestructiveButton: String
  var body: some View {
    let minimumLongPressDuration = 0.3
    let longPress =
      LongPressGesture(
        minimumDuration: minimumLongPressDuration
      )
      .sequenced(
        before: DragGesture(minimumDistance: 0)
      )
      .updating($pressState) { value, state, _ in
        switch value {
        case .first:
          state = .activated
        case .second:
          state = .confirmed
        }
      }
      .onEnded { value in
        guard case .second = value else { return }
        self.viewState.toggle()
        self.showingAlert = true
        action()
      }

    Button(action: {}, label: {
      label
        .symbolRenderingMode(.hierarchical)
        .scaleEffect(pressState.isPressing ? 1.4 : 1)
        .animation(.easeOut(duration: minimumLongPressDuration),
                   value: pressState.isPressing)
        .gesture(longPress)
    })
    // .alert(alertMessage, isPresented: $showingAlert) {
    //   Button("Cancel", role: .cancel) {}
    //   Button(alertDestructiveButton, role: .destructive) {}
    // }
  }

  // MARK: Private

  @GestureState private var pressState = PressState.idle
  @State private var showingAlert = false
}

// MARK: - PressState

private enum PressState {
  /// **Default state**.
  /// The button is ready to be activiated.
  case idle
  /// The button with enough duration long pressing.
  case activated
  /// The button has recently switched on/off.
  case confirmed

  // MARK: Internal

  var isPressing: Bool {
    switch self {
    case .activated:
      return true
    case .confirmed, .idle:
      return false
    }
  }
}

// MARK: - LongPressButton_Previews

struct LongPressButton_Previews: PreviewProvider {
  static var previews: some View {
    LongPressButton(label: {
      Image(systemName: "checkmark.circle.fill")
        .font(.system(size: 64))
    }, action: {})
      .frame(width: 64, height: 64, alignment: .center)
      .foregroundColor(.red)
  }
}