Detect if the user scrolls in SwiftUI

ScrollViewDelegate.swift

struct ScrollViewDelegate<Content: View>: View {

  @State private var verticalScrollTimer: Timer?
  @State private var horizontalScrollTimer: Timer?
  @ViewBuilder private let content: Content
  private let axes: Axis.Set
  private let showsIndicators: Bool
  private let onVerticalScroll: ((_ isScrolling: Bool) -> Void)?
  private let onHorizontalScroll: ((_ isScrolling: Bool) -> Void)?
  private let coordinateSpace = "scrollView"
  private let scrollDetectorInterval = 0.25

  init(_ axes: Axis.Set = .vertical,
       showsIndicators: Bool = true,
       @ViewBuilder content: () -> Content,
       onVerticalScroll: ((_ isScrolling: Bool) -> Void)? = nil,
       onHorizontalScroll: ((_ isScrolling: Bool) -> Void)? = nil) {
    self.axes = axes
    self.showsIndicators = showsIndicators
    self.content = content()
    self.onVerticalScroll = axes.contains(.vertical) ? onVerticalScroll : nil
    self.onHorizontalScroll = axes.contains(.horizontal) ? onHorizontalScroll : nil
  }

  var body: some View {
    ScrollView(axes, showsIndicators: showsIndicators) {
      content
        .background {
          GeometryReader { proxy in
            Color.clear.preference(key: YOffsetKey.self, value: -proxy.frame(in: .named(coordinateSpace)).minY)
            Color.clear.preference(key: XOffsetKey.self, value: -proxy.frame(in: .named(coordinateSpace)).minX)
          }
        }
    }
    .coordinateSpace(name: coordinateSpace)
    .onPreferenceChange(YOffsetKey.self) { value in
      guard axes.contains(.vertical) else { return }
      verticalScrollTimer?.invalidate()
      verticalScrollTimer = Timer.scheduledTimer(withTimeInterval: scrollDetectorInterval, repeats: false) { _ in
        onVerticalScroll?(false)
      }
      onVerticalScroll?(value > 0)
    }
    .onPreferenceChange(XOffsetKey.self) { value in
      guard axes.contains(.horizontal) else { return }
      horizontalScrollTimer?.invalidate()
      horizontalScrollTimer = Timer.scheduledTimer(withTimeInterval: scrollDetectorInterval, repeats: false) { _ in
        onHorizontalScroll?(false)
      }
      onHorizontalScroll?(value > 0)
    }
  }
}

private struct YOffsetKey: PreferenceKey {

  static var defaultValue: CGFloat = .zero

  static func reduce(value: inout Value, nextValue: () -> Value) {
    value += nextValue()
  }
}

private struct XOffsetKey: PreferenceKey {

  static var defaultValue: CGFloat = .zero

  static func reduce(value: inout Value, nextValue: () -> Value) {
    value += nextValue()
  }
}