SwiftUI Crash when scrolling a list

Question

Glad to post my first question here!

I've been playing around with SwiftUI for a few weeks now and during a bigger project, I found the following bug.

If you have a TabView and a list inside it, if you try to change the tab while the scroll animation takes place, the app will crash with FATAL ERROR: "Thread 1: signal SIGABRT".

Console:

BugTest[11830:362796] precondition failure: attribute failed to set an initial value: 98

Have you ever encountered this? Is there any way I can solve this issue without changing my list into a ForEach?

Thank you in advance!

Code:

import SwiftUI

struct ContentView: View {
    var body: some View {
                TabView {
                    list()
                        .tabItem {
                            Image(systemName: "doc")
                                .font(.system(size: 25))
                    }

                    Text("Testing the bug")
                        .tabItem {
                            Image(systemName: "list.dash")
                                .font(.system(size: 25))
                    }
        }
    }
}

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

struct list: View {

    var body: some View {
        List(0..<50){_ in
            Text("test")
        }
    }
}

Cannot reproduce. Xcode 11.2.1 (11B500) / iOS 13.2.2. Please try to wrap your list in `VStack` container, by my observations it is buggy to use dynamic-size views (like `List`, `ScrollView`) at top level of `body` — Asperi, Nov 29 '19 at 05:56
I embedded the list in a VStack but with no luck. I will stick to ForEach until this gets fixed. Thank you for your answer! — Catalin Olaru, Nov 29 '19 at 16:31
Which Xcode/iOS versions do you use? Just to know. With such type of system level error it is good practice to note which environment is used. Thanks. — Asperi, Nov 29 '19 at 16:34
I will attach a video below so you can see the issue I am facing — Catalin Olaru, Nov 30 '19 at 00:20
I cannot reproduce this error either. Using iPhone on iOS 13.3 and XCode Version 11.3 beta. — simibac, Nov 30 '19 at 19:02
@SimonBachmann let me download the beta and I will come back with an update — Catalin Olaru, Nov 30 '19 at 20:32
@SimonBachmann I still encounter the issue even on 13.3. Please take a moment to watch this video we.tl/t-GM5K90xJjG — Catalin Olaru, Dec 01 '19 at 01:03
Cannot reproduce any more with Xcode 11.4 beta (11N111s) in Simulator and on iPhone 8 with iOS 13.4 beta (17E5223h) — Gunter Hager, Feb 12 '20 at 12:17

score -2 · Answer 1 · answered Dec 01 '19 at 04:14

According to this post, the error occurred because the items in the list were not conforming to the Identifiable protocol.

struct ContentView: View {
    var body: some View {
        TabView {
            list()
                .tabItem {
                    Image(systemName: "doc")
                        .font(.system(size: 25))
            }

            Text("Testing the bug")
                .tabItem {
                    Image(systemName: "list.dash")
                        .font(.system(size: 25))
            }
        }
    }
}

struct list: View {
    var elements: [CustomInt] = []

    init() {
        for i in 0...1000{
            elements.append(CustomInt(text:String(i)))
        }
    }

    var body: some View {
        List(elements){element in
            Text(element.text)
        }
    }
}

struct CustomInt: Identifiable{
    var id = UUID()
    var text:String
}

Mohamed Wasiq · Accepted Answer · 2020-04-07T05:24:53.557

-3

This should work

struct ContentView: View {
var body: some View {
            TabView {
               VStack{
                list()
                    .tabItem {
                        Image(systemName: "doc")
                            .font(.system(size: 25))
                }

                Text("Testing the bug")
                    .tabItem {
                        Image(systemName: "list.dash")
                            .font(.system(size: 25))
                }
    }
}
}}

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

struct list: View {
var body: some View {
    List(0..<50){_ in
        Text("test")
    }
}}

edited Apr 07 '20 at 05:24

answered Dec 18 '19 at 15:47

Mohamed Wasiq

490
4
17

Thank you very much! I slightly modified your version and it works in my case – Catalin Olaru Dec 20 '19 at 00:18
Could you please explain the difference? Why that works? Looks like you simply removed his code to call list() – norekhov Jan 21 '20 at 14:48
1

I see - you tried to put it in VStack. For me it doesn't help. Replacing with ForEach also doesn't help. – norekhov Jan 21 '20 at 15:02
Don’t know but it weirdly works in my case. SwiftUI has lot of bugs with List. Could you try with Scroll View ? Or post the code where it doesn’t work for you. – Mohamed Wasiq Jan 21 '20 at 18:17
I edited the code a bit but looks like could you please check? Looks like putting all tabs inside VStack is not what OP wanted. In this edition TabView won't show tabs at all I think. – norekhov Jan 21 '20 at 19:40

SwiftUI Crash when scrolling a list

2 Answers2