RefreshControl.swift

import SwiftUI

struct RefreshControl: View {
    var coordinateSpace: CoordinateSpace
    var onRefresh: ()->Void
    @State var refresh: Bool = false
    var body: some View {
        GeometryReader { geo in
            if (geo.frame(in: coordinateSpace).midY > 50) {
                Spacer()
                    .onAppear {
                        if refresh == false {
                            onRefresh() ///call refresh once if pulled more than 50px
                        }
                        refresh = true
                    }
            } else if (geo.frame(in: coordinateSpace).maxY < 1) {
                Spacer()
                    .onAppear {
                        refresh = false
                        ///reset  refresh if view shrink back
                    }
            }
            ZStack(alignment: .center) {
                if refresh { ///show loading if refresh called
                    ProgressView()
                } else { ///mimic static progress bar with filled bar to the drag percentage
                    ForEach(0..<8) { tick in
                          VStack {
                              Rectangle()
                                .fill(Color(UIColor.tertiaryLabel))
                                .opacity((Int((geo.frame(in: coordinateSpace).midY)/7) < tick) ? 0 : 1)
                                  .frame(width: 3, height: 7)
                                .cornerRadius(3)
                              Spacer()
                      }.rotationEffect(Angle.degrees(Double(tick)/(8) * 360))
                   }.frame(width: 20, height: 20, alignment: .center)
                }
            }.frame(width: geo.size.width)
        }.padding(.top, -50)
    }
}

struct PullToRefreshDemo: View {
    var body: some View {
        ScrollView {
            RefreshControl(coordinateSpace: .named("RefreshControl")) {
                //refresh view here
            }
            Text("Some view...")
        }.coordinateSpace(name: "RefreshControl")
    }
}

struct PullToRefreshDemo_Previews: PreviewProvider {
    static var previews: some View {
        PullToRefreshDemo()
    }
}

Nice! It works as advertised.

I'd like to offer a small tweak so that its only responsibility is its presentation like UIRefreshControl.

Instead of passing in the closure onRefresh, I pass in the binding isRefreshing. Now, the parent can react to isRefreshing and call its own closure.

This also gives the parent control over when to end refreshing. (needs another tweak to adjust the padding to show the spinner while isRefreshing is true)