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

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)
            }
        })
    }
}

@d03090 might be ugly, but it works

@d03090 I tried using your solution and it works well and is smooth, however when I embed it in a scrollview the scroll disabled or broken. Any idea how to enable scrolling?

Have made my own adjustment to the original to get drag gestures working just like the original PageTabViewStyle. Also uses the predicted swipe end that @d03090 implements and also limits the scroll to one page at a time. FYI @gesabo - This implementation works with a nested ScrollView. Tested on Xcode 12.4, iOS 14.4. Thank you @mecid for the original code!
https://gist.github.com/wtpalexander/565ccf7bb092734dbf2c584dd639fb46

@wtpalexander thanks for that, unfortunately it still doesn't solve my UI. My view hierarchy is like this: Master View that has the PagerView as a Child, and the PagerView has 3 subviews that need to be able to be scrolled vertically. Ideally I would like the Master View to have a ScrollView so that when the subviews content is scrolled, the Large Title in the Navigation Bar become small. The problem is when I add a ScrollView to Master View, it seems as though PagerView prevents the vertical scrolling and won't let me fully scroll.

@gesabo Apologies - I miss understood your requirements! So you'd like a scroll view that snaps to each page, but when scrolled to the second or third nested view, the NavBar changes from LargeTitle to Inline?

@wtpalexander yes it seems that if the PagerView is embedded in a ScrollView then the sub views of the PagerView are not scrollable. Again my view hierarchy is Master View -> PagerView -> Subviews. For now I have the subviews having ScrollViews, which works to scroll vertically to see their content, however the large title the nav bar doesn't change to inline. Ideally I would like to remove the ScrollView from the subviews and place it in the MasterView so I can get this functionality where the large title changes to inline.

@mecid / @d03090 / @gesabo
Just my two cents, as often as possible I prefer to use the real-thing given Apple usually does a far more complete implementation for other things like accessibility. In addition, the animations and gesture implementations are more consistent across iOS versions. In that vein, I've created an implementation that just wraps TabView and provides auto-sizing based on the content (height).

Since it wraps TabView the API is identical and it behaves exactly as expected. Feel free to grab it here if it works for your needs:
https://gist.github.com/shaps80/65d9d58480469bfe8eff6542f1dd16c4

@wtpalexander I tried your solution but I found the gestures to be very 'sticky' and difficult to work with, maybe this works for you too? 👍

My team recently delivered PagerTabStripView, a new Open Source for Pager Tab views. This is the GitHub repo. You can read an introduction in this post.
Here is an example gif!

We'll appreciate it if you can take a look! If you like the library, want to contribute to the project, or need some help using it, please reach out to us, open an issue or a pull request.

This will more smoothly

import Foundation
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)
            .animation(.linear, value: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)
            }
        })
    }
}

Is there any way to load the views lazily?

@samilao101 did you try to use LazyHStack instead of HStack?

@mecid I did, but the issue is that in order for a lazyhstack to become lazy it needs to be imbedded in a scrollview, and if you do that, you essentially lose the pagination feature.

@samilao101 oh, you're right. Maybe TabView with Page style will work for you better?

So isn't the lazy this approach....Load all contents and onAppear

@pjcau sorry I am not sure I understand what you mean

@pjcau sorry I am not sure I understand what you mean

IN this way, if you want load a array of DetalView for example, so load in one step all init and onAppear(). So it's not good. But fix it with TabView with Page style.

@pjcau did you manage to integrate ScrollView in order to achieve lazy loading?