final class ScrollDelegate: NSObject, UITableViewDelegate, UIScrollViewDelegate {
    var isScrolling: Binding<Bool>?
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        if let isScrolling = isScrolling?.wrappedValue,!isScrolling {
            self.isScrolling?.wrappedValue = true
        }
    }
    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        if let isScrolling = isScrolling?.wrappedValue, isScrolling {
            self.isScrolling?.wrappedValue = false
        }
    }
    // 手指緩慢拖動(dòng)可滾動(dòng)控件，手指離開(kāi)后，decelerate 為 false，因此并不會(huì)調(diào)用 scrollViewDidEndDecelerating 方法
    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        if !decelerate {
            if let isScrolling = isScrolling?.wrappedValue, isScrolling {
                self.isScrolling?.wrappedValue = false
            }
        }
    }
}
extension View {
    func scrollStatusByIntrospect(isScrolling: Binding<Bool>) -> some View {
        modifier(ScrollStatusByIntrospectModifier(isScrolling: isScrolling))
    }
}
struct ScrollStatusByIntrospectModifier: ViewModifier {
    @State var delegate = ScrollDelegate()
    @Binding var isScrolling: Bool
    func body(content: Content) -> some View {
        content
            .onAppear {
                self.delegate.isScrolling = $isScrolling
            }
            // 同時(shí)支持 ScrollView 和 List
            .introspectScrollView { scrollView in
                scrollView.delegate = delegate
            }
            .introspectTableView { tableView in
                tableView.delegate = delegate
            }
    }
}

struct ScrollStatusByIntrospect: View {
    @State var isScrolling = false
    var body: some View {
        VStack {
            Text("isScrolling: \(isScrolling1 ? "True" : "False")")
            List {
                ForEach(0..<100) { i in
                    Text("id:\(i)")
                }
            }
            .scrollStatusByIntrospect(isScrolling: $isScrolling)
        }
    }
}

final class ExclusionStore: ObservableObject {
    @Published var isScrolling = false
    // 當(dāng) Runloop 處于 default（ kCFRunLoopDefaultMode ）模式時(shí)，每隔 0.1 秒會(huì)發(fā)送一個(gè)時(shí)間信號(hào)
    private let idlePublisher = Timer.publish(every: 0.1, on: .main, in: .default).autoconnect()
    // 當(dāng) Runloop 處于 tracking（ UITrackingRunLoopMode ）模式時(shí)，每隔 0.1 秒會(huì)發(fā)送一個(gè)時(shí)間信號(hào)
    private let scrollingPublisher = Timer.publish(every: 0.1, on: .main, in: .tracking).autoconnect()
    private var publisher: some Publisher {
        scrollingPublisher
            .map { _ in 1 } // 滾動(dòng)時(shí)，發(fā)送 1
            .merge(with:
                idlePublisher
                    .map { _ in 0 } // 不滾動(dòng)時(shí)，發(fā)送 0
            )
    }
    var cancellable: AnyCancellable?
    init() {
        cancellable = publisher
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: { _ in }, receiveValue: { output in
                guard let value = output as? Int else { return }
                if value == 1,!self.isScrolling {
                    self.isScrolling = true
                }
                if value == 0, self.isScrolling {
                    self.isScrolling = false
                }
            })
    }
}
struct ScrollStatusMonitorExclusionModifier: ViewModifier {
    @StateObject private var store = ExclusionStore()
    @Binding var isScrolling: Bool
    func body(content: Content) -> some View {
        content
            .environment(\.isScrolling, store.isScrolling)
            .onChange(of: store.isScrolling) { value in
                isScrolling = value
            }
            .onDisappear {
                store.cancellable = nil // 防止內(nèi)存泄露
            }
    }
}

final class CommonStore: ObservableObject {
    @Published var isScrolling = false
    private var timestamp = Date()
    let preferencePublisher = PassthroughSubject<Int, Never>()
    let timeoutPublisher = PassthroughSubject<Int, Never>()
    private var publisher: some Publisher {
        preferencePublisher
            .dropFirst(2) // 改善進(jìn)入視圖時(shí)可能出現(xiàn)的狀態(tài)抖動(dòng)
            .handleEvents(
                receiveOutput: { _ in
                    self.timestamp = Date() 
                    // 如果 0.15 秒后沒(méi)有繼續(xù)收到位置變化的信號(hào)，則發(fā)送滾動(dòng)狀態(tài)停止的信號(hào)
                    DispatchQueue.main.asyncAfter(deadline: .now() + 0.15) {
                        if Date().timeIntervalSince(self.timestamp) > 0.1 {
                            self.timeoutPublisher.send(0)
                        }
                    }
                }
            )
            .merge(with: timeoutPublisher)
    }
    var cancellable: AnyCancellable?
    init() {
        cancellable = publisher
            .receive(on: DispatchQueue.main)
            .sink(receiveCompletion: { _ in }, receiveValue: { output in
                guard let value = output as? Int else { return }
                if value == 1,!self.isScrolling {
                    self.isScrolling = true
                }
                if value == 0, self.isScrolling {
                    self.isScrolling = false
                }
            })
    }
}
public struct MinValueKey: PreferenceKey {
    public static var defaultValue: CGRect = .zero
    public static func reduce(value: inout CGRect, nextValue: () -> CGRect) {
        value = nextValue()
    }
}
struct ScrollStatusMonitorCommonModifier: ViewModifier {
    @StateObject private var store = CommonStore()
    @Binding var isScrolling: Bool
    func body(content: Content) -> some View {
        content
            .environment(\.isScrolling, store.isScrolling)
            .onChange(of: store.isScrolling) { value in
                isScrolling = value
            }
        // 接收來(lái)自子視圖的位置信息
            .onPreferenceChange(MinValueKey.self) { _ in
                store.preferencePublisher.send(1) // 我們不關(guān)心具體的位置信息，只需將其標(biāo)注為滾動(dòng)中
            }
            .onDisappear {
                store.cancellable = nil
            }
    }
}
// 添加與 ScrollView、List 的子視圖之上，用于在位置發(fā)生變化時(shí)發(fā)送信息
func scrollSensor() -> some View {
    overlay(
        GeometryReader { proxy in
            Color.clear
                .preference(
                    key: MinValueKey.self,
                    value: proxy.frame(in: .global)
                )
        }
    )
}

struct VStackExclusionDemo: View {
    @State var isScrolling = false
    var body: some View {
        VStack {
            ScrollView {
                VStack {
                    ForEach(0..<100) { i in
                        CellView(index: i) // no need to add sensor in exclusion mode
                    }
                }
            }
            .scrollStatusMonitor($isScrolling, monitorMode: .exclusion) // add scrollStatusMonitor to get scroll status
        }
    }
}

struct ListCommonDemo: View {
    @State var isScrolling = false
    var body: some View {
        VStack {
            List {
                ForEach(0..<100) { i in
                    CellView(index: i)
                        .scrollSensor() // Need to add sensor for each subview
                }
            }
            .scrollStatusMonitor($isScrolling, monitorMode: .common)
        }
    }
}