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@xtabbas
Created May 10, 2020 18:13
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A carousel that snap items in place build on top of SwiftUI
//
// SnapCarousel.swift
// prototype5
//
// Created by xtabbas on 5/7/20.
// Copyright © 2020 xtadevs. All rights reserved.
//
import SwiftUI
struct SnapCarousel: View {
@EnvironmentObject var UIState: UIStateModel
var body: some View {
let spacing: CGFloat = 16
let widthOfHiddenCards: CGFloat = 32 /// UIScreen.main.bounds.width - 10
let cardHeight: CGFloat = 279
let items = [
Card(id: 0, name: "Hey"),
Card(id: 1, name: "Ho"),
Card(id: 2, name: "Lets"),
Card(id: 3, name: "Go")
]
return Canvas {
/// TODO: find a way to avoid passing same arguments to Carousel and Item
Carousel(
numberOfItems: CGFloat(items.count),
spacing: spacing,
widthOfHiddenCards: widthOfHiddenCards
) {
ForEach(items, id: \.self.id) { item in
Item(
_id: Int(item.id),
spacing: spacing,
widthOfHiddenCards: widthOfHiddenCards,
cardHeight: cardHeight
) {
Text("\(item.name)")
}
.foregroundColor(Color.white)
.background(Color("surface"))
.cornerRadius(8)
.shadow(color: Color("shadow1"), radius: 4, x: 0, y: 4)
.transition(AnyTransition.slide)
.animation(.spring())
}
}
}
}
}
struct Card: Decodable, Hashable, Identifiable {
var id: Int
var name: String = ""
}
public class UIStateModel: ObservableObject {
@Published var activeCard: Int = 0
@Published var screenDrag: Float = 0.0
}
struct Carousel<Items : View> : View {
let items: Items
let numberOfItems: CGFloat //= 8
let spacing: CGFloat //= 16
let widthOfHiddenCards: CGFloat //= 32
let totalSpacing: CGFloat
let cardWidth: CGFloat
@GestureState var isDetectingLongPress = false
@EnvironmentObject var UIState: UIStateModel
@inlinable public init(
numberOfItems: CGFloat,
spacing: CGFloat,
widthOfHiddenCards: CGFloat,
@ViewBuilder _ items: () -> Items) {
self.items = items()
self.numberOfItems = numberOfItems
self.spacing = spacing
self.widthOfHiddenCards = widthOfHiddenCards
self.totalSpacing = (numberOfItems - 1) * spacing
self.cardWidth = UIScreen.main.bounds.width - (widthOfHiddenCards*2) - (spacing*2) //279
}
var body: some View {
let totalCanvasWidth: CGFloat = (cardWidth * numberOfItems) + totalSpacing
let xOffsetToShift = (totalCanvasWidth - UIScreen.main.bounds.width) / 2
let leftPadding = widthOfHiddenCards + spacing
let totalMovement = cardWidth + spacing
let activeOffset = xOffsetToShift + (leftPadding) - (totalMovement * CGFloat(UIState.activeCard))
let nextOffset = xOffsetToShift + (leftPadding) - (totalMovement * CGFloat(UIState.activeCard) + 1)
var calcOffset = Float(activeOffset)
if (calcOffset != Float(nextOffset)) {
calcOffset = Float(activeOffset) + UIState.screenDrag
}
return HStack(alignment: .center, spacing: spacing) {
items
}
.offset(x: CGFloat(calcOffset), y: 0)
.gesture(DragGesture().updating($isDetectingLongPress) { currentState, gestureState, transaction in
self.UIState.screenDrag = Float(currentState.translation.width)
}.onEnded { value in
self.UIState.screenDrag = 0
if (value.translation.width < -50) {
self.UIState.activeCard = self.UIState.activeCard + 1
let impactMed = UIImpactFeedbackGenerator(style: .medium)
impactMed.impactOccurred()
}
if (value.translation.width > 50) {
self.UIState.activeCard = self.UIState.activeCard - 1
let impactMed = UIImpactFeedbackGenerator(style: .medium)
impactMed.impactOccurred()
}
})
}
}
struct Canvas<Content : View> : View {
let content: Content
@EnvironmentObject var UIState: UIStateModel
@inlinable init(@ViewBuilder _ content: () -> Content) {
self.content = content()
}
var body: some View {
content
.frame(minWidth: 0, maxWidth: .infinity, minHeight: 0, maxHeight: .infinity, alignment: .center)
.background(Color.white.edgesIgnoringSafeArea(.all))
}
}
struct Item<Content: View>: View {
@EnvironmentObject var UIState: UIStateModel
let cardWidth: CGFloat
let cardHeight: CGFloat
var _id: Int
var content: Content
@inlinable public init(
_id: Int,
spacing: CGFloat,
widthOfHiddenCards: CGFloat,
cardHeight: CGFloat,
@ViewBuilder _ content: () -> Content
) {
self.content = content()
self.cardWidth = UIScreen.main.bounds.width - (widthOfHiddenCards*2) - (spacing*2) //279
self.cardHeight = cardHeight
self._id = _id
}
var body: some View {
content
.frame(width: cardWidth, height: _id == UIState.activeCard ? cardHeight : cardHeight - 60, alignment: .center)
}
}
struct SnapCarousel_Previews: PreviewProvider {
static var previews: some View {
SnapCarousel()
}
}
@danielaRiesgo
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In case it's useful for anyone: the id of the items must equal their index in order to correctly set their height when scrolling.
Or what I did was set the _id of Item to the index value but set the real view id to the real one that depends on the data.

@llieusedie
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Is there a way I can dynamically change the background color (slide transition) depending on a current item in a carousel?

For example, each card represents a topic, like "Nature", "Art", "Sports", etc. How do I change the background color when the user chooses one of the topics?

@GefeiSHEN
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GefeiSHEN commented Jan 10, 2023

Any one encountered this runtime warning? Is there a way to resolve this warning?

Publishing changes from within view updates is not allowed, this will cause undefined behavior.


update: this should be an Xcode 14 specific issue, please refer to https://developer.apple.com/forums/thread/711899

@MartinLBarron
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Great snippet and article. I was wondering if anyone else solved the issue GefeiShHEN noted:

Publishing changes from within view updates is not allowed, this will cause undefined behavior.

The forum post he referred to returns 404 and googling around didn't find any obvious fix.

@GefeiSHEN
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GefeiSHEN commented Mar 16, 2023

Great snippet and article. I was wondering if anyone else solved the issue GefeiShHEN noted:

Publishing changes from within view updates is not allowed, this will cause undefined behavior.

The forum post he referred to returns 404 and googling around didn't find any obvious fix.

Hi @MartinLBarron! Please try to click on that link again, it shall be fixed now. Alternatively, you could try copy and paste the url directly to your browser.

@hankyungs
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hankyungs commented Apr 13, 2023

It looks slow when dragging. so I teak little bit

.animation(.spring())
to
.animation(UIState.screenDrag == 0 ? .easeOut : .linear(duration: 0), value: UIState.screenDrag)

@alwacker
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alwacker commented Jul 3, 2023

Hi @xtabbas, thanks for amazing solution. It really help to find way out!

I would like consider a small improvement in case bouncing at start and the end:

  1. Add translation wrapper property
    @GestureState var translation: CGFloat = 0

  2. In .updating method of gesture you should update this translation property.Like here:
    .updating($translation) { value, out, _ in out = value.translation.width self.UIState.screenDrag = Float(value.translation.width) }

  3. After that, using it for calculation offset
    CGFloat(calcOffset) - (translation / 2)
    This one will create a scroll limit in the beginning of carousel, and at the end!

Cheers!

@andreaagudo3
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Hi @xtabbas, thanks for amazing solution. It really help to find way out!

I would like consider a small improvement in case bouncing at start and the end:

  1. Add translation wrapper property
    @GestureState var translation: CGFloat = 0
  2. In .updating method of gesture you should update this translation property.Like here:
    .updating($translation) { value, out, _ in out = value.translation.width self.UIState.screenDrag = Float(value.translation.width) }
  3. After that, using it for calculation offset
    CGFloat(calcOffset) - (translation / 2)
    This one will create a scroll limit in the beginning of carousel, and at the end!

Cheers!

Would you mind sharing your approach?

@noveleven
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in NavigavionView set .navigationViewStyle(StackNavigationViewStyle()), There will be a bug back.

add clipped() to Canvas view to remove offset part.

return Canvas {
    /// TODO: find a way to avoid passing same arguments to Carousel and Item
    Carousel(
        numberOfItems: CGFloat(items.count),
        spacing: spacing,
        widthOfHiddenCards: widthOfHiddenCards
    ) {
        ForEach(items, id: \.self.id) { item in
            Item(
                _id: Int(item.id),
                spacing: spacing,
                widthOfHiddenCards: widthOfHiddenCards,
                cardHeight: cardHeight
            ) {
                Text("\(item.name)")
            }
            .foregroundColor(Color.white)
            .background(.black)
            .cornerRadius(8)
            .shadow(color: .gray, radius: 4, x: 0, y: 4)
            .transition(AnyTransition.slide)
            .animation(.spring())
        }
    }
}
.clipped() <- here!

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