SwiftUI List/Form bad animation when adding/removing rows

Question

I have a really simple list with text that when the user taps on it, it expands with a datepicker inside.

The problem is that the animation looks really broken, not sure what I can do about this besides doing the entire thing from scratch, that at this point I'd rather just use UIKit.

If you have an idea of how this can be fixed I'd really appreciate.

Here's the code:

struct ContentView: View {
    let items = ["123", "345", "678"]
    @State private var selectedItems = Set<String>()
    @State private var test = Date()

    var body: some View {
        Form {
            ForEach(items.indices) { index in
                Button(action: {
                    withAnimation {
                        if selectedItems.contains(items[index]) {
                            selectedItems.remove(items[index])
                        } else {
                            selectedItems.insert(items[index])
                        }
                    }
                }, label: {
                    Text(items[index])
                        .foregroundColor(.primary)
                })
                if selectedItems.contains(items[index]) {
                    DatePicker(selection: $test, in: ...Date(), displayedComponents: .date) {
                            }
                    .datePickerStyle(WheelDatePickerStyle())
                }
            }
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

Does this answer your question stackoverflow.com/a/62650979/12299030? — Asperi
– Asperi, Commented Sep 26, 2020 at 19:23

pawello2222 · Accepted Answer · 2020-09-26 18:01:40Z

3

ForEach(content:) should only be used for static collections.

If you have a dynamic collection (such as in your example - you're adding/removing entries), you need to use ForEach(id:content:):

ForEach(items.indices, id: \.self) { index in

Note that if your collection can have duplicate items, then id: \.self will not work properly and you may need to create a struct conforming to Identifiable instead.

edited Sep 26, 2020 at 18:01

answered Sep 26, 2020 at 17:54

pawello2222

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1 Comment

Wak Over a year ago

Changing to ForEach(items.indices, id: \.self) { index in made no difference on the animation glitch =/

JIE WANG · Accepted Answer · 2020-09-26 20:37:28Z

Use Section inside ForEach.

struct ContentView: View {
    let items = ["123", "345", "678"]
    @State private var selectedItems = Set<String>()
    @State private var test = Date()

    var body: some View {
        Form {
            ForEach(items.indices) { index in
                Section(header: header(index), content: {
                    if selectedItems.contains(items[index]) {
                        DatePicker(selection: $test, in: ...Date(), displayedComponents: .date) {
                                }
                        .datePickerStyle(WheelDatePickerStyle())
                    }
                })
            }
        }
    }
    
    private func header(_ index: Int) -> some View {
        Button(action: {
            withAnimation {
                if selectedItems.contains(items[index]) {
                    selectedItems.remove(items[index])
                } else {
                    selectedItems.insert(items[index])
                }
            }
        }, label: {
            Text(items[index])
                .foregroundColor(.primary)
        })
    }
}

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