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Last active February 7, 2024 00:46
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// Authoer: The SwiftUI Lab
// Full article: https://swiftui-lab.com/scrollview-pull-to-refresh/
import SwiftUI
struct RefreshableScrollView<Content: View>: View {
@State private var previousScrollOffset: CGFloat = 0
@State private var scrollOffset: CGFloat = 0
@State private var frozen: Bool = false
@State private var rotation: Angle = .degrees(0)
var threshold: CGFloat = 80
@Binding var refreshing: Bool
let content: Content
init(height: CGFloat = 80, refreshing: Binding<Bool>, @ViewBuilder content: () -> Content) {
self.threshold = height
self._refreshing = refreshing
self.content = content()
}
var body: some View {
return VStack {
ScrollView {
ZStack(alignment: .top) {
MovingView()
VStack { self.content }.alignmentGuide(.top, computeValue: { d in (self.refreshing && self.frozen) ? -self.threshold : 0.0 })
SymbolView(height: self.threshold, loading: self.refreshing, frozen: self.frozen, rotation: self.rotation)
}
}
.background(FixedView())
.onPreferenceChange(RefreshableKeyTypes.PrefKey.self) { values in
self.refreshLogic(values: values)
}
}
}
func refreshLogic(values: [RefreshableKeyTypes.PrefData]) {
DispatchQueue.main.async {
// Calculate scroll offset
let movingBounds = values.first { $0.vType == .movingView }?.bounds ?? .zero
let fixedBounds = values.first { $0.vType == .fixedView }?.bounds ?? .zero
self.scrollOffset = movingBounds.minY - fixedBounds.minY
self.rotation = self.symbolRotation(self.scrollOffset)
// Crossing the threshold on the way down, we start the refresh process
if !self.refreshing && (self.scrollOffset > self.threshold && self.previousScrollOffset <= self.threshold) {
self.refreshing = true
}
if self.refreshing {
// Crossing the threshold on the way up, we add a space at the top of the scrollview
if self.previousScrollOffset > self.threshold && self.scrollOffset <= self.threshold {
self.frozen = true
}
} else {
// remove the sapce at the top of the scroll view
self.frozen = false
}
// Update last scroll offset
self.previousScrollOffset = self.scrollOffset
}
}
func symbolRotation(_ scrollOffset: CGFloat) -> Angle {
// We will begin rotation, only after we have passed
// 60% of the way of reaching the threshold.
if scrollOffset < self.threshold * 0.60 {
return .degrees(0)
} else {
// Calculate rotation, based on the amount of scroll offset
let h = Double(self.threshold)
let d = Double(scrollOffset)
let v = max(min(d - (h * 0.6), h * 0.4), 0)
return .degrees(180 * v / (h * 0.4))
}
}
struct SymbolView: View {
var height: CGFloat
var loading: Bool
var frozen: Bool
var rotation: Angle
var body: some View {
Group {
if self.loading { // If loading, show the activity control
VStack {
Spacer()
ActivityRep()
Spacer()
}.frame(height: height).fixedSize()
.offset(y: -height + (self.loading && self.frozen ? height : 0.0))
} else {
Image(systemName: "arrow.down") // If not loading, show the arrow
.resizable()
.aspectRatio(contentMode: .fit)
.frame(width: height * 0.25, height: height * 0.25).fixedSize()
.padding(height * 0.375)
.rotationEffect(rotation)
.offset(y: -height + (loading && frozen ? +height : 0.0))
}
}
}
}
struct MovingView: View {
var body: some View {
GeometryReader { proxy in
Color.clear.preference(key: RefreshableKeyTypes.PrefKey.self, value: [RefreshableKeyTypes.PrefData(vType: .movingView, bounds: proxy.frame(in: .global))])
}.frame(height: 0)
}
}
struct FixedView: View {
var body: some View {
GeometryReader { proxy in
Color.clear.preference(key: RefreshableKeyTypes.PrefKey.self, value: [RefreshableKeyTypes.PrefData(vType: .fixedView, bounds: proxy.frame(in: .global))])
}
}
}
}
struct RefreshableKeyTypes {
enum ViewType: Int {
case movingView
case fixedView
}
struct PrefData: Equatable {
let vType: ViewType
let bounds: CGRect
}
struct PrefKey: PreferenceKey {
static var defaultValue: [PrefData] = []
static func reduce(value: inout [PrefData], nextValue: () -> [PrefData]) {
value.append(contentsOf: nextValue())
}
typealias Value = [PrefData]
}
}
struct ActivityRep: UIViewRepresentable {
func makeUIView(context: UIViewRepresentableContext<ActivityRep>) -> UIActivityIndicatorView {
return UIActivityIndicatorView()
}
func updateUIView(_ uiView: UIActivityIndicatorView, context: UIViewRepresentableContext<ActivityRep>) {
uiView.startAnimating()
}
}
@DmitryBespalov
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Hi there, what license is this code available with?

@swiftui-lab
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Author

Hi there, what license is this code available with?

MIT License ;-)

@cjhodge
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cjhodge commented Jul 21, 2020

Does not work on iOS 14 (beta 2).

@cjhodge
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cjhodge commented Aug 6, 2020

Working on iOS 14 beta 4!

@Pyroscout
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My view resizes to be way too big sometimes when I am refreshing. Any idea on how to prevent that?

@DmitryBespalov
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Just FYI, we are using this solution in most of the screens that use "List" but it brought crashes when we released to production. Currently, the only option I found to fix those crashes is to implement refreshing without pull to refresh - just using a "reload" button.

@syasann
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syasann commented Oct 16, 2020

fantastic work friend!it seems to be the result of your countless attempts.

@alexxcheung
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It totally works!

@kutakmir
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kutakmir commented Feb 6, 2021

Hey, please don't use this code. If you keep on refreshing the view hierarchy like this it will cause you performance issues.

Use Swift introspect instead + the underlying UIScrollView. Much better performance.

These are the limitations of SwiftUI we have to live with at the moment. Peace.

@ouabbas
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ouabbas commented Feb 27, 2021

Hey, please don't use this code. If you keep on refreshing the view hierarchy like this it will cause you performance issues.

Use Swift introspect instead + the underlying UIScrollView. Much better performance.

These are the limitations of SwiftUI we have to live with at the moment. Peace.

Hey, you're right ! My app lag very much... Do you have a github repo where i can see how you do for "the pull to refresh" feature please please thanks !

@plaps153
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plaps153 commented Apr 1, 2021

Hey, please don't use this code. If you keep on refreshing the view hierarchy like this it will cause you performance issues.

Use Swift introspect instead + the underlying UIScrollView. Much better performance.

These are the limitations of SwiftUI we have to live with at the moment. Peace.

But you can't use LayVStack, LazyHStack with UIScrollView. That's why I can't go back to UIScrollView.

@MrEldin
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MrEldin commented Jun 24, 2021

Hi, I have an issue, when I push scroll and left it before data are completely loaded, I have the small bounce of the scroll view content and the loader is showing under the content, all the time when data are coming from the ajax call?

I got it to work just fine when I commented out these lines of code:

if self.previousScrollOffset > self.threshold && self.scrollOffset <= self.threshold {
    self.frozen = true
}

So I am not adding extra space because data are coming faster than space is created and I have a small bounce when the loader is shown.

Do you have any suggestions?

Thank you.

@jevonmao
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Does not work well with NavigationView's large navigation title

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