dynamic list with sections producing strange behaviour / crashes - swiftui

Question

OK, I nailed down the problem to the dynamic list with sections, so I changed the title and I'm going to shorten my post...
In my project, there is a complex view that contains a dynamic list with sections that depend on many state variables.
Problem: after a few user interactions and subsequent changes to the list, I see strange behaviour:
sometimes a section doesn't show up although the condition of the if-clause in which it is embedded is definitely met
sometimes, the section header label is replaced with the label of a list item
sometimes, it crashes
when the view is broken and I enforce a refresh of the view without changing any of the state variables, everything looks good again
The code below is taken from my project, however, greatly simplified by removing parts that are not necessary to produce the error. The state variable altered by user interaction is pIdStatus. From pIdStatus, the function data.analyze() calculates the arrays pastriesWithStatus1, pastriesWithStatus2 and pastriesWithStatus3.
Interestingly, when I remove the tab-view in which everything is embedded, everything works fine.
Any help is greatly appreciated.
import SwiftUI
struct ContentView: View {
#StateObject var data = Data()
var body: some View {
TabView { // needed in my project and needed for crash.
List {
// for debugging purpose: create a button that triggers a refresh
Button {
data.counter += 1
} label: {
HStack() {
Text("Refresh")
.font(.system(size: 16, weight: .regular))
}
}
// Section with status3-items
if data.pastriesWithStatus3.count > 0 {
Section(header:
HStack() {
Text("STATUS 3")
}
){
ForEach(data.pastriesWithStatus3, id: \.self) { i in
subview21(data: data, label: data.pastries.first(where: { $0.id == i })!.name, id: i, status: 3)
}
}
}
// section with other items
Section(header:
HStack() {
Text("OTHER ITEMS")
}
){
ForEach(data.pastriesWithStatus2, id: \.self) { i in
subview21(data: data, label: data.pastries.first(where: { $0.id == i })!.name, id: i, status: 2)
}
ForEach(data.pastriesWithStatus1, id: \.self) { i in
subview21(data: data, label: data.pastries.first(where: { $0.id == i })!.name, id: i, status: 1)
}
}
}
.listStyle(InsetGroupedListStyle())
.tabItem {
Image(systemName: "cart")
Text("shopping")
}.onAppear {
data.analyze()
}
}
}
}
struct subview21: View {
#ObservedObject var data : Data
let hspacing: CGFloat = 20
let tab1: CGFloat = 150
var label: String
var id: Int
var status: Int // 1=red, 2=unchecked, 3=green
var body: some View {
if data.testcondition { // this line is required for crash. Although it is always true.
HStack (spacing: hspacing) {
Text(data.pastries.first(where: { $0.id == id })!.name)
.frame(width: tab1, alignment: .leading)
Button {
data.pIdStatus[id] = 1
data.analyze()
} label: {
Image(systemName: (status == 1 ? "checkmark.square.fill" : "square"))
.foregroundColor(.red)
}
.buttonStyle(BorderlessButtonStyle())
Button {
data.pIdStatus[id] = 3
data.analyze()
} label: {
Image(systemName: (status == 3 ? "checkmark.square.fill" : "square"))
.foregroundColor(.green)
}
.buttonStyle(BorderlessButtonStyle())
}
}
}
}
let maxPId = 99
struct Person: Identifiable, Hashable {
let id: Int
let name: String
var orders: [Order]
}
struct Pastry: Identifiable, Hashable {
let id: Int
let name: String
}
struct Order: Hashable {
var pastryId: Int
var n: Int
var otherwise: OrderL2?
}
struct OrderL2: Hashable {
let level: Int = 2
var pastryId: Int
var n: Int
}
class Data : ObservableObject {
#Published var persons: [Person] = [
Person(id: 1, name: "John", orders: [Order(pastryId: 0, n:1, otherwise:OrderL2(pastryId: 1, n:2))]),
]
#Published var pastries: [Pastry] = [Pastry(id: 0, name: "Donut"),
Pastry(id: 1, name: "prezel")]
#Published var counter: Int = 0 // for debugging
#Published var pIdStatus: [Int] = Array(repeating: 2, count: maxPId)
#Published var testcondition: Bool = true // needed in my project, for simplicity, here, always true
#Published var pastriesWithStatus1: [Int] = []
#Published var pastriesWithStatus2: [Int] = []
#Published var pastriesWithStatus3: [Int] = []
func analyze() {
var localPastriesWithStatus1: [Int] = []
var localPastriesWithStatus2: [Int] = []
var localPastriesWithStatus3: [Int] = []
for p in pastries { // there may be more elegant ways to code, however, in real life, there's a lot more functionality here
if p.id < maxPId {
if pIdStatus[p.id] == 1 {
localPastriesWithStatus1.append(p.id)
}
if pIdStatus[p.id] == 2 {
localPastriesWithStatus2.append(p.id)
}
if pIdStatus[p.id] == 3 {
localPastriesWithStatus3.append(p.id)
}
}
}
pastriesWithStatus1 = localPastriesWithStatus1
pastriesWithStatus2 = localPastriesWithStatus2
pastriesWithStatus3 = localPastriesWithStatus3
}
}

Answer 1

Apparently, swiftui List is not made for Lists that are built from scratch each time the view is refreshed. Instead, Lists must be linked to arrays to/from which items are added/removed one by one.
I solved the problem by avoiding List altogether, instead using Stack, Text etc.