refresh.swift

import SwiftUI

struct PullToRefreshSample: View {

    let items = [
        "one", "two", "three", "four", "five"
    ]

    @State private var isRefreshing = true

    var body: some View {
        
        List(items, id: \.self) { item in
            Text(item)
        }
        .navigationBarTitle("My List")
        .pullToRefresh(isRefreshing: $isRefreshing) {

            print("refreshing...")

            DispatchQueue.main.asyncAfter(deadline: .now() + 2) {

                print("done...")
                self.isRefreshing = false
            }
        }
    }
}

struct RefreshControl: UIViewRepresentable {

    @Binding var isRefreshing: Bool
    let refreshHandler: () -> Void

    init(isRefreshing: Binding<Bool>, refreshHandler: @escaping () -> Void) {
        _isRefreshing = isRefreshing
        self.refreshHandler = refreshHandler
    }

    class Coordinator {

        let isRefreshing: Binding<Bool>
        let refreshHandler: () -> Void

        init(isRefreshing: Binding<Bool>, refreshHandler: @escaping () -> Void) {
            self.isRefreshing = isRefreshing
            self.refreshHandler = refreshHandler
        }

        @objc
        func refresh() {
            isRefreshing.wrappedValue = true
            refreshHandler()
        }
    }

    func makeCoordinator() -> Coordinator {
        Coordinator(isRefreshing: $isRefreshing, refreshHandler: refreshHandler)
    }

    func makeUIView(context: UIViewRepresentableContext<RefreshControl>) -> UIView {
        let view = UIView(frame: .zero)
        view.isHidden = true
        view.isUserInteractionEnabled = false
        return view
    }

    func updateUIView(_ uiView: UIView, context: UIViewRepresentableContext<RefreshControl>) {

        // this gets called a lot early, without the dispatch it doesn't work
        // TODO - find out why
        //
        DispatchQueue.main.asyncAfter(deadline: .now()) {

            guard let tableView = self.findTableView(from: uiView) else {
                return
            }

            if let refreshControl = tableView.refreshControl {
                if self.isRefreshing {
                    refreshControl.beginRefreshing()
                } else {
                    refreshControl.endRefreshing()
                }
                return
            }

            let refreshControl = UIRefreshControl()
            refreshControl.addTarget(context.coordinator, action: #selector(Coordinator.refresh), for: .valueChanged)
            tableView.refreshControl = refreshControl
        }
    }

    private func findTableView(from view: UIView) -> UITableView? {

        var tableView: UITableView?

        if let tv = view.findChild(ofType: UITableView.self) {
            tableView = tv
        } else if let tv = view.findChildInAncestors(ofType: UITableView.self) {
            tableView = tv
        } else if let tv = view.findChildInSiblings(ofType: UITableView.self) {
            tableView = tv
        }

        return tableView
    }
}

extension UIView {

    func findChild<T>(ofType type: T.Type) -> T? {

        for subview in subviews {
            if let t = subview as? T {
                return t
            }
        }

        for subview in subviews {
            if let foundInChild = subview.findChild(ofType: type) {
                return foundInChild
            }
        }

        return nil
    }


    func findChild<T>(ofType type: T.Type, in view: UIView) -> T? {
        return view.findChild(ofType: type)
    }

    func findChildInAncestors<T>(ofType type: T.Type) -> T? {

        var sv = superview

        while let s = sv {
            if let t = s.findChildInSiblings(ofType: type) {
                return t
            }
            sv = s.superview
        }

        return nil
    }

    func findChildInSiblings<T>(ofType type: T.Type) -> T? {
        guard let superview = superview else { return nil }

        for sibling in superview.subviews.filter( { $0 != self } ).reversed() {
            if let t = sibling.findChild(ofType: type) {
                return t
            }
        }

        return nil
    }
}

extension View {
    public func pullToRefresh(isRefreshing: Binding<Bool>, refreshHandler: @escaping () -> Void) -> some View {
        return overlay(
            RefreshControl(isRefreshing: isRefreshing, refreshHandler: refreshHandler)
                .frame(width: 0, height: 0)
        )
    }
}

struct PullToRefreshSample_Previews: PreviewProvider {
    static var previews: some View {
        PullToRefreshSample()
    }
}