DelegateEnabledScrollView with iOS 17 or lower.

README.md

DelegateEnabledScrollView

DelegateEnabledScrollView is a custom SwiftUI view that facilitates the use of UIScrollViewDelegate's event handlers within a SwiftUI context. This enables you to easily implement custom behaviors based on UIScrollView's scroll events in SwiftUI.

Usage

1. Content Provision: When initializing DelegateEnabledScrollView, you provide the content that will be displayed. This is done through a closure that takes an optional UIScrollView as an argument and returns a view.

2. Event Handlers: You can chain methods corresponding to each UIScrollViewDelegate event (like onDidScroll, onWillEndDragging, etc.) to the view. These methods take closures as arguments, allowing you to set custom actions for each event.

3. Layout Adjustments: Adjust the layout as needed using SwiftUI view modifiers like .frame.

DelegateEnabledScrollView.swift

import SwiftUI
@_spi(Advanced) import SwiftUIIntrospect

struct DelegateEnabledScrollView<Content: View>: View {
    @State private var scrollViewDelegate: DelegateEnabledScrollViewDelegate?
    @State private var scrollView: UIScrollView? = nil
    let content: (UIScrollView?) -> Content

    var onDidZoom: ((UIScrollView) -> Void)?
    var onWillBeginDragging: ((UIScrollView) -> Void)?
    var onDidScroll: ((UIScrollView) -> Void)?
    var onDidEndDecelerating: ((UIScrollView) -> Void)?
    var onWillBeginDecelerating: ((UIScrollView) -> Void)?
    var onDidScrollToTop: ((UIScrollView) -> Void)?
    var onShouldScrollToTop: ((UIScrollView) -> Bool)?
    var onDidEndScrollingAnimation: ((UIScrollView) -> Void)?
    var onWillBeginZooming: ((UIScrollView, UIView?) -> Void)?
    var onDidChangeAdjustedContentInset: ((UIScrollView) -> Void)?
    var onDidEndDragging:((UIScrollView, Bool) -> Void)?
    var onDidEndZooming:((UIScrollView, UIView?, CGFloat) -> Void)?
    var onWillEndDragging:((UIScrollView, CGPoint, UnsafeMutablePointer<CGPoint>) -> Void)?
    
    init(@ViewBuilder content: @escaping (UIScrollView?) -> Content,
         onDidZoom: ((UIScrollView) -> Void)? = nil,
         onWillBeginDragging: ((UIScrollView) -> Void)? = nil,
         onDidScroll: ((UIScrollView) -> Void)? = nil,
         onDidEndDecelerating: ((UIScrollView) -> Void)? = nil,
         onWillBeginDecelerating: ((UIScrollView) -> Void)? = nil,
         onDidScrollToTop: ((UIScrollView) -> Void)? = nil,
         onShouldScrollToTop: ((UIScrollView) -> Bool)? = nil,
         onDidEndScrollingAnimation: ((UIScrollView) -> Void)? = nil,
         onWillBeginZooming: ((UIScrollView, UIView?) -> Void)? = nil,
         onDidChangeAdjustedContentInset: ((UIScrollView) -> Void)? = nil,
         onDidEndDragging: ((UIScrollView, Bool) -> Void)? = nil,
         onDidEndZooming: ((UIScrollView, UIView?, CGFloat) -> Void)? = nil,
         onWillEndDragging: ((UIScrollView, CGPoint, UnsafeMutablePointer<CGPoint>) -> Void)? = nil
    ) {
        self.content = content
        self.onDidZoom = onDidZoom
        self.onWillBeginDragging = onWillBeginDragging
        self.onDidScroll = onDidScroll
        self.onDidEndDecelerating = onDidEndDecelerating
        self.onWillBeginDecelerating = onWillBeginDecelerating
        self.onDidScrollToTop = onDidScrollToTop
        self.onShouldScrollToTop = onShouldScrollToTop
        self.onDidEndScrollingAnimation = onDidEndScrollingAnimation
        self.onWillBeginZooming = onWillBeginZooming
        self.onDidChangeAdjustedContentInset = onDidChangeAdjustedContentInset
        self.onDidEndDragging = onDidEndDragging
        self.onDidEndZooming = onDidEndZooming
        self.onWillEndDragging = onWillEndDragging
    }

    var body: some View {
        ScrollViewReader { proxy in
            ScrollView {
                content(self.scrollView)
            }
            .onAppear {
                self.scrollViewDelegate = DelegateEnabledScrollViewDelegate(
                    onDidScroll: onDidScroll ?? { _ in },
                    onWillBeginDragging: onWillBeginDragging ?? { _ in },
                    onDidEndDecelerating: onDidEndDecelerating ?? { _ in },
                    onWillBeginDecelerating: onWillBeginDecelerating ?? { _ in },
                    onDidScrollToTop: onDidScrollToTop ?? { _ in },
                    onShouldScrollToTop: onShouldScrollToTop ?? { _ in true },
                    onDidEndScrollingAnimation: onDidEndScrollingAnimation ?? { _ in },
                    onWillBeginZooming: onWillBeginZooming ?? { _, _ in },
                    onDidChangeAdjustedContentInset: onDidChangeAdjustedContentInset ?? { _ in },
                    onDidEndDragging: onDidEndDragging ?? { _, _ in },
                    onDidEndZooming: onDidEndZooming ?? { _, _, _ in },
                    onWillEndDragging: onWillEndDragging ?? { _, _, _ in }
                )
            }
            .introspect(.scrollView, on: .iOS(.v13, .v14, .v15, .v16, .v17)) { _scrollView in
                self.scrollView = _scrollView
                self.scrollView!.delegate = self.scrollViewDelegate
            }
        }
    }
    
    func onDidScroll(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidScroll = action
        return view
    }

    func onWillBeginDragging(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onWillBeginDragging = action
        return view
    }

    func onDidEndDecelerating(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidEndDecelerating = action
        return view
    }

    func onWillBeginDecelerating(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onWillBeginDecelerating = action
        return view
    }

    func onDidScrollToTop(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidScrollToTop = action
        return view
    }

    func onShouldScrollToTop(_ action: @escaping (_ scrollView: UIScrollView) -> Bool) -> DelegateEnabledScrollView {
        var view = self
        view.onShouldScrollToTop = action
        return view
    }

    func onDidEndScrollingAnimation(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidEndScrollingAnimation = action
        return view
    }

    func onWillBeginZooming(_ action: @escaping (_ scrollView: UIScrollView, _ view: UIView?) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onWillBeginZooming = action
        return view
    }

    func onDidChangeAdjustedContentInset(_ action: @escaping (_ scrollView: UIScrollView) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidChangeAdjustedContentInset = action
        return view
    }

    func onDidEndDragging(_ action: @escaping (_ scrollView: UIScrollView, _ decelerate: Bool) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidEndDragging = action
        return view
    }

    func onDidEndZooming(_ action: @escaping (_ scrollView: UIScrollView, _ view: UIView?, _ scale: CGFloat) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onDidEndZooming = action
        return view
    }

    func onWillEndDragging(_ action: @escaping (_ scrollView: UIScrollView, _ velocity: CGPoint, _ targetContentOffset: UnsafeMutablePointer<CGPoint>) -> Void) -> DelegateEnabledScrollView {
        var view = self
        view.onWillEndDragging = action
        return view
    }

}



class DelegateEnabledScrollViewDelegate: NSObject, UIScrollViewDelegate {
    var onDidScroll: ((UIScrollView) -> Void)
    var onWillBeginDragging: ((UIScrollView) -> Void)
    var onDidEndDecelerating: ((UIScrollView) -> Void)
    var onWillBeginDecelerating: ((UIScrollView) -> Void)
    var onDidScrollToTop: ((UIScrollView) -> Void)
    var onShouldScrollToTop: ((UIScrollView) -> Bool)
    var onDidEndScrollingAnimation: ((UIScrollView) -> Void)
    var onWillBeginZooming: ((UIScrollView, UIView?) -> Void)
    var onDidChangeAdjustedContentInset: ((UIScrollView) -> Void)
    var onDidEndDragging: ((UIScrollView, Bool) -> Void)
    var onDidEndZooming: ((UIScrollView, UIView?, CGFloat) -> Void)
    var onWillEndDragging: ((UIScrollView, CGPoint, UnsafeMutablePointer<CGPoint>) -> Void)

    init(
        onDidScroll: @escaping ((UIScrollView) -> Void),
        onWillBeginDragging: @escaping ((UIScrollView) -> Void),
        onDidEndDecelerating: @escaping ((UIScrollView) -> Void),
        onWillBeginDecelerating: @escaping ((UIScrollView) -> Void),
        onDidScrollToTop: @escaping ((UIScrollView) -> Void),
        onShouldScrollToTop: @escaping ((UIScrollView) -> Bool),
        onDidEndScrollingAnimation: @escaping ((UIScrollView) -> Void),
        onWillBeginZooming: @escaping ((UIScrollView, UIView?) -> Void),
        onDidChangeAdjustedContentInset: @escaping ((UIScrollView) -> Void),
        onDidEndDragging: @escaping ((UIScrollView, Bool) -> Void),
        onDidEndZooming: @escaping ((UIScrollView, UIView?, CGFloat) -> Void),
        onWillEndDragging: @escaping ((UIScrollView, CGPoint, UnsafeMutablePointer<CGPoint>) -> Void)
    ) {
        self.onDidScroll = onDidScroll
        self.onWillBeginDragging = onWillBeginDragging
        self.onDidEndDecelerating = onDidEndDecelerating
        self.onWillBeginDecelerating = onWillBeginDecelerating
        self.onDidScrollToTop = onDidScrollToTop
        self.onShouldScrollToTop = onShouldScrollToTop
        self.onDidEndScrollingAnimation = onDidEndScrollingAnimation
        self.onWillBeginZooming = onWillBeginZooming
        self.onDidChangeAdjustedContentInset = onDidChangeAdjustedContentInset
        self.onDidEndDragging = onDidEndDragging
        self.onDidEndZooming = onDidEndZooming
        self.onWillEndDragging = onWillEndDragging
    }

    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        onDidScroll(scrollView)
    }

    func scrollViewWillBeginDragging(_ scrollView: UIScrollView) {
        onWillBeginDragging(scrollView)
    }

    func scrollViewDidEndDecelerating(_ scrollView: UIScrollView) {
        onDidEndDecelerating(scrollView)
    }

    func scrollViewWillBeginDecelerating(_ scrollView: UIScrollView) {
        onWillBeginDecelerating(scrollView)
    }

    func scrollViewDidScrollToTop(_ scrollView: UIScrollView) {
        onDidScrollToTop(scrollView)
    }

    func scrollViewShouldScrollToTop(_ scrollView: UIScrollView) -> Bool {
        return onShouldScrollToTop(scrollView)
    }

    func scrollViewDidEndScrollingAnimation(_ scrollView: UIScrollView) {
        onDidEndScrollingAnimation(scrollView)
    }

    func scrollViewWillBeginZooming(_ scrollView: UIScrollView, with view: UIView?) {
        onWillBeginZooming(scrollView, view)
    }

    func scrollViewDidChangeAdjustedContentInset(_ scrollView: UIScrollView) {
        onDidChangeAdjustedContentInset(scrollView)
    }

    func scrollViewDidEndDragging(_ scrollView: UIScrollView, willDecelerate decelerate: Bool) {
        onDidEndDragging(scrollView, decelerate)
    }

    func scrollViewDidEndZooming(_ scrollView: UIScrollView, with view: UIView?, atScale scale: CGFloat) {
        onDidEndZooming(scrollView, view, scale)
    }

    func scrollViewWillEndDragging(_ scrollView: UIScrollView, withVelocity velocity: CGPoint, targetContentOffset: UnsafeMutablePointer<CGPoint>) {
        onWillEndDragging(scrollView, velocity, targetContentOffset)
    }
}


struct _Previewer: View {
    @State private var lastEvent = ""

    var body: some View {
        GeometryReader { geometry in
            VStack {
                ScrollView {
                    Text(lastEvent)
                        .frame(maxWidth: .infinity, minHeight: geometry.size.height / 3, alignment: .leading)
                        .background(Color(.systemGray4))
                }

                DelegateEnabledScrollView { scrollView in
                    LazyVStack {
                        ForEach(0..<100, id: \.self) { index in
                            Text("Item \(index)")
                                .id(index)
                        }
                    }
                }
                .onWillEndDragging { scrollView, velocity, targetContentOffset in
                    lastEvent = "onWillEndDragging: \(velocity), \(targetContentOffset.pointee)"
                }
                .frame(height: geometry.size.height * 2 / 3)
            }
        }
    }
}

#Preview {
    _Previewer()
}