PagerView in SwiftUI

PagerView.swift

//
//  PagerView.swift
//
//  Created by Majid Jabrayilov on 12/5/19.
//  Copyright © 2019 Majid Jabrayilov. All rights reserved.
//
import SwiftUI

struct PagerView<Content: View>: View {
    let pageCount: Int
    @Binding var currentIndex: Int
    let content: Content

    @GestureState private var translation: CGFloat = 0

    init(pageCount: Int, currentIndex: Binding<Int>, @ViewBuilder content: () -> Content) {
        self.pageCount = pageCount
        self._currentIndex = currentIndex
        self.content = content()
    }

    var body: some View {
        GeometryReader { geometry in
            HStack(spacing: 0) {
                self.content.frame(width: geometry.size.width)
            }
            .frame(width: geometry.size.width, alignment: .leading)
            .offset(x: -CGFloat(self.currentIndex) * geometry.size.width)
            .offset(x: self.translation)
            .animation(.interactiveSpring())
            .gesture(
                DragGesture().updating(self.$translation) { value, state, _ in
                    state = value.translation.width
                }.onEnded { value in
                    let offset = value.translation.width / geometry.size.width
                    let newIndex = (CGFloat(self.currentIndex) - offset).rounded()
                    self.currentIndex = min(max(Int(newIndex), 0), self.pageCount - 1)
                }
            )
        }
    }
}

@mecid How would you solve animation on the pages? now when I have a animation set to a page the whole thing starts animating when I drag

@mecid How would you solve animation on the pages? now when I have a animation set to a page the whole thing starts animating when I drag

I'm not sure I understand the problem, could you please describe it?

@majid Here is a sample + relevant code https://gist.github.com/Plnda/121b5960807074cf5fd68c68f959aa54

@majid Here is a sample + relevant code https://gist.github.com/Plnda/121b5960807074cf5fd68c68f959aa54

Interesting issue, you can add animation(nil) modifier to the content inside PagerView, I think it should help.

@mecid A bug I noticed (which I've seen in some other apps) when you are switching between vertical scroll views diagonally, all objects will shift horizontally and remain that way until you scroll horizontally again to the next page. Is there a way to disable horizontal scrolling while you are scrolling vertically?
Also, what would change scroll sensitivity?
Edit: found another bug, where an image does not update until the end of the transition.

I've added a Page Control at bottom.

import SwiftUI

struct PagerView<Content: View>: View {
    let pageCount: Int
    @Binding var currentIndex: Int
    let content: Content

    @GestureState private var translation: CGFloat = 0

    init(pageCount: Int, currentIndex: Binding<Int>, @ViewBuilder content: () -> Content) {
        self.pageCount = pageCount
        self._currentIndex = currentIndex
        self.content = content()
    }

    var body: some View {
        GeometryReader { geometry in
            ZStack {
                HStack(spacing: 0) {
                    self.content.frame(width: geometry.size.width)
                }
                .frame(width: geometry.size.width, alignment: .leading)
                .offset(x: -CGFloat(self.currentIndex) * geometry.size.width)
                .offset(x: self.translation)
                .animation(.interactiveSpring())
                .gesture(
                    DragGesture().updating(self.$translation) { value, state, _ in
                        state = value.translation.width
                    }.onEnded { value in
                        let offset = value.translation.width / geometry.size.width
                        let newIndex = (CGFloat(self.currentIndex) - offset).rounded()
                        self.currentIndex = min(max(Int(newIndex), 0), self.pageCount - 1)
                    }
                )
                
                VStack {
                    Spacer()
                    
                    HStack {
                        ForEach(0..<self.pageCount, id: \.self) { index in
                            Circle()
                                .fill(index == self.currentIndex ? Color.white : Color.gray)
                                .frame(width: 10, height: 10)
                        }
                    }
                }
                .offset(y: 16)
            }
        }
    }
}

@fnazarios that is great! Thanks 🙏🏻

@majid Here is a sample + relevant code https://gist.github.com/Plnda/121b5960807074cf5fd68c68f959aa54

Interesting issue, you can add animation(nil) modifier to the content inside PagerView, I think it should help.

Did you guys found a solution for this problem? I still facing the problem. :(

@mmosimann disabling animation with .animation(nil) or applying it by withAnimation should solve the issue.

Hello! I have tried to make the animation a bit smoother and also tried to use predictedEndTranslation for faster swiping through. I had to change the currentIndex from Int to Float for it to work. Now I'm struggling to get the Binding back to Int, because an Int Index would definitely make more sense.
I would be glad, if you would tell me what you think about the changes and do you know how I can change the Binding back to an Int? Is this possible with Custom Bindings or something like that?

import SwiftUI

struct PagerView<Content: View>: View {
    let pageCount: Int
    @Binding var currentIndex: Int
    @State var currentFloatIndex: CGFloat = 0
    let content: Content

    @GestureState private var offsetX: CGFloat = 0

    init(pageCount: Int, currentIndex: Binding<Int>, @ViewBuilder content: () -> Content) {
        self.pageCount = pageCount
        self._currentIndex = currentIndex
        self.content = content()
    }

    var body: some View {
        GeometryReader { geometry in
            HStack(spacing: 0) {
                self.content.frame(width: geometry.size.width)
            }
            .frame(width: geometry.size.width, alignment: .leading)
            .offset(x: -CGFloat(self.currentFloatIndex) * geometry.size.width)
            .offset(x: self.offsetX)
            .highPriorityGesture(
                DragGesture().updating(self.$offsetX) { value, state, _ in
                    state = value.translation.width
                }
                .onEnded({ (value) in
                    let offset = value.translation.width / geometry.size.width
                    let offsetPredicted = value.predictedEndTranslation.width / geometry.size.width
                    let newIndex = CGFloat(self.currentFloatIndex) - offset
                    
                    self.currentFloatIndex = newIndex
                    
                    withAnimation(.easeOut) {
                        if(offsetPredicted < -0.5 && offset > -0.5) {
                            self.currentFloatIndex = CGFloat(min(max(Int(newIndex.rounded() + 1), 0), self.pageCount - 1))
                        } else if (offsetPredicted > 0.5 && offset < 0.5) {
                            self.currentFloatIndex = CGFloat(min(max(Int(newIndex.rounded() - 1), 0), self.pageCount - 1))
                        } else {
                            self.currentFloatIndex = CGFloat(min(max(Int(newIndex.rounded()), 0), self.pageCount - 1))
                        }
                    }
                })
            )
        }
    }
}

@d03090 The animation looks very nice. Have you found a solution for Binding?

@Degtyarserg

Thanks. I just have a VERY UGLY solution and I would be very happy, if someone can do it better.

import SwiftUI

struct PagerView<Content: View>: View {
    let pageCount: Int
    @State var ignore: Bool = false
    @Binding var currentIndex: Int {
        didSet {
            if (!ignore) {
                currentFloatIndex = CGFloat(currentIndex)
            }
        }
    }
    @State var currentFloatIndex: CGFloat = 0 {
        didSet {
            ignore = true
            currentIndex = min(max(Int(currentFloatIndex.rounded()), 0), self.pageCount - 1)
            ignore = false
        }
    }
    let content: Content

    @GestureState private var offsetX: CGFloat = 0

    init(pageCount: Int, currentIndex: Binding<Int>, @ViewBuilder content: () -> Content) {
        self.pageCount = pageCount
        self._currentIndex = currentIndex
        self.content = content()
    }

    var body: some View {
        GeometryReader { geometry in
            HStack(spacing: 0) {
                self.content.frame(width: geometry.size.width)
            }
            .frame(width: geometry.size.width, alignment: .leading)
            .offset(x: -CGFloat(self.currentFloatIndex) * geometry.size.width)
            .offset(x: self.offsetX)
            .highPriorityGesture(
                DragGesture().updating(self.$offsetX) { value, state, _ in
                    state = value.translation.width
                }
                .onEnded({ (value) in
                    let offset = value.translation.width / geometry.size.width
                    let offsetPredicted = value.predictedEndTranslation.width / geometry.size.width
                    let newIndex = CGFloat(self.currentFloatIndex) - offset
                    
                    self.currentFloatIndex = newIndex
                    
                    withAnimation(.easeOut) {
                        if(offsetPredicted < -0.5 && offset > -0.5) {
                            self.currentFloatIndex = CGFloat(min(max(Int(newIndex.rounded() + 1), 0), self.pageCount - 1))
                        } else if (offsetPredicted > 0.5 && offset < 0.5) {
                            self.currentFloatIndex = CGFloat(min(max(Int(newIndex.rounded() - 1), 0), self.pageCount - 1))
                        } else {
                            self.currentFloatIndex = CGFloat(min(max(Int(newIndex.rounded()), 0), self.pageCount - 1))
                        }
                    }
                })
            )
        }
        .onChange(of: currentIndex, perform: { value in
            print("index changed")
            
            // this is probably animated twice, if the tab change occurs because of the drag gesture
            withAnimation(.easeOut) {
                currentFloatIndex = CGFloat(value)
            }
        })
    }
}