SwiftUI - How to animate components corresponding to array elements?

Question

I have an HStack of circles in SwiftUI, and the number of circles is determined based on the length of an array, like this:

@State var myArr = [...]
...
ScrollView(.horizontal) {
  HStack {
    ForEach(myArr) { item in
      Circle()
      //.frame(...)
      //.animation(...) I tried this, it didn't work
    }
  }
}

Then I have a button that appends an element to this array, effectively adding a circle to the view:

Button {
  myArr.append(...)
} label: {
  ...
}

The button works as intended, however, the new circle that is added to the view appears very abruptly, and seems choppy. How can I animate this in any way? Perhaps it slides in from the side, or grows from a very small circle to its normal size.

swiftPunk · Accepted Answer · 2022-02-18 21:44:06Z

2

You are missing transition, here is what you looking:

 struct ContentView: View {
    
    @State private var array: [Int] = Array(0...2)
    
    var body: some View {
        
        ScrollView(.horizontal) {
            HStack {
                ForEach(array, id:\.self) { item in
                    
                    Circle()
                        .frame(width: 50, height: 50)
                        .transition(AnyTransition.scale)
                    
                }
            }
        }
        .animation(.default, value: array.count)
        
        
        Button("add new circle") {
            array.append(array.count)
        }
        
        Button("remove a circle") {
            if array.count > 0 {
                array.remove(at: array.count  - 1)
            }
        }
 
    }
}

answered Feb 18, 2022 at 21:44

swiftPunk

1

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Comments

ChrisR · Accepted Answer · 2022-02-18 22:32:18Z

0

a version with automatic scroll to the last circle:

struct myItem: Identifiable, Equatable {
    let id = UUID()
    var size: CGFloat
}

struct ContentView: View {
    
    @State private var myArr: [myItem] = [
        myItem(size: 10),
        myItem(size: 40),
        myItem(size: 30)
    ]
    
    var body: some View {
        
        ScrollViewReader { scrollProxy in
            VStack(alignment: .leading) {
                Spacer()
                
                ScrollView(.horizontal) {
                    HStack {
                        ForEach(myArr) { item in
                            Circle()
                                .id(item.id)
                                .frame(width: item.size, height: item.size)
                                .transition(.scale)
                        }
                    }
                }
                .animation(.easeInOut(duration: 1), value: myArr)
                
                Spacer()
                
                Button("Add One") {
                    let new = myItem(size: CGFloat.random(in: 10...100))
                    myArr.append(new)
                }
                
                .onChange(of: myArr) { _ in
                    withAnimation {
                        scrollProxy.scrollTo(myArr.last!.id, anchor: .trailing)
                    }
                }
                
                .frame(maxWidth: .infinity, alignment: .center)
            }
            .padding()
        }
    }
}

answered Feb 18, 2022 at 22:32

ChrisR

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6 Comments

Nicolas Gimelli Over a year ago

when i add your animation, the scroll goes to the last circle, but it cuts off part of it on the side, do you know how I could fix this?

ChrisR Over a year ago

on which side does it cut off?

Nicolas Gimelli Over a year ago

nevermind it was a padding issue, thank you for your response anyway! :)

ChrisR Over a year ago

puuh ... I'm glad ;)

Nicolas Gimelli Over a year ago

although I will say that the scroll is a little bit glitchy, almost like the scroll is being "forced" (kind of like it rubber bands). any idea on how to fix that?

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