index out of bound from TabViewStyle of SwiftUI - ios

Question

I am trying to implement a tabView that takes a list of items into pages that I could swipe back and forth. However, it keeps bugging out with an "index out of bound" error. It's confusing to me because I never set index at all, and I don't know how to force an index either...
Below are my code. Apologize for any naive code, I am new to SwiftUI. Any helps are appreciated, thank you!
import SwiftUI
//#Published private var list = QuestionList.self
struct QuestionList: Codable {
var list:[QuestionItem]
}
class QuestionItem: Codable, Identifiable {
var id: Int
var text: String
var type: Int
var answer: String
}
struct ContentView: View {
#State private var qlist = [QuestionItem]()
#State private var isShowForm = false
#State private var q1 = true
#State private var answer = ""
#State private var isOn = [Bool]()
#State private var selectedTab = 0
func showForm() {
isShowForm = !isShowForm
let url = URL(string: "http://127.0.0.1:3000/question")!
let task = URLSession.shared.dataTask(with: url) {
data, response, error in
if let error = error {
print(error)
return
}
guard let httpResponse = response as? HTTPURLResponse,
(200...299).contains(httpResponse.statusCode) else {
print(response)
return
}
guard let data = data else {
return
}
do {
let list = try JSONDecoder().decode([QuestionItem].self, from:data)
qlist = list
print(qlist[1])
for i in 0..<qlist.count {
isOn.append(qlist[i].type == 0)
}
print(isOn)
// print(isOn)
print(type(of: qlist[1]))
} catch {
print("error: ", error)
}
}
task.resume()
}
var body: some View {
Text("Hello, world!")
.padding()
Button("Open Form") {
self.showForm()
}
if (isShowForm) {
TabView(selection: $selectedTab) {
ForEach(qlist.indices, id: \.self) { index in
if qlist[index].type == 0 {
HStack {
Text("\(self.qlist[index].text)")
// Toggle("", isOn: $isOn[index])
Toggle("", isOn: $q1)
}
} else {
VStack {
Text("\(self.qlist[index].text)")
// .lineLimit(2)
// .multilineTextAlignment(.leading)
.fixedSize(horizontal: false, vertical: true)
// .frame(width: 300)
TextField("Enter your answer here:", text: $qlist[index].answer) {
}
}
}
}
}
.tabViewStyle(.page(indexDisplayMode: .always))
.indexViewStyle(.page(backgroundDisplayMode: .always))
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}

Answer 1

It is not recommended to use indices in ForEach loops, instead use something like this updated code
that allows you to use your TextField :
ForEach($qlist) { $qItem in // <-- here $
if qItem.type == 0 {
HStack {
Text(qItem.text)
// Toggle("", isOn: $isOn[index])
Toggle("", isOn: $q1)
}
} else {
VStack {
Text(qItem.text)
// .lineLimit(2)
// .multilineTextAlignment(.leading)
.fixedSize(horizontal: false, vertical: true)
// .frame(width: 300)
TextField("Enter your answer here:", text: $qItem.answer) {
}
}
}
}
and as I mentioned in my comment, remove the print(qlist[1]) and print(type(of: qlist[1])) in showForm,
because if qlist is empty or only has one element, you will get the index out of bound error .
Remember one element is qlist[0].
EDIT-1: full test code:
this is the code I used in my test. It does not give any index errors.
import SwiftUI
#main
struct TestApp: App {
var body: some Scene {
WindowGroup {
ContentView()
}
}
}
struct ContentView: View {
#State var qlist = [QuestionItem]()
#State private var isShowForm = false
#State private var q1 = true
#State private var answer = ""
#State private var isOn = [Bool]()
#State private var selectedTab = 0
func showForm() {
let url = URL(string: "http://127.0.0.1:3000/question")!
let task = URLSession.shared.dataTask(with: url) {
data, response, error in
if let error = error {
print(error)
return
}
guard let httpResponse = response as? HTTPURLResponse,
(200...299).contains(httpResponse.statusCode) else {
// print(response)
return
}
guard let data = data else {
return
}
do {
let list = try JSONDecoder().decode([QuestionItem].self, from:data)
qlist = list
// print(qlist[1])
for i in 0..<qlist.count {
isOn.append(qlist[i].type == 0)
}
print(isOn)
// print(isOn)
// print(type(of: qlist[1]))
isShowForm.toggle() // <--- here important
} catch {
print("error: ", error)
}
}
task.resume()
}
var body: some View {
Text("Hello, world!")
.padding()
Button("Open Form") {
// self.showForm()
// simulate showForm()
qlist = [
QuestionItem(id: 0, text: "text0", type: 0, answer: "0"),
QuestionItem(id: 1, text: "text1", type: 1, answer: "1"),
QuestionItem(id: 2, text: "text2", type: 2, answer: "2"),
QuestionItem(id: 3, text: "text3", type: 3, answer: "3")
]
isShowForm.toggle() // <--- here after qlist is set
}
if (isShowForm) {
TabView(selection: $selectedTab) {
ForEach($qlist) { $qItem in
if qItem.type == 0 {
HStack {
Text(qItem.text)
// Toggle("", isOn: $isOn[index])
Toggle("", isOn: $q1)
}
} else {
VStack {
Text(qItem.text)
// .lineLimit(2)
// .multilineTextAlignment(.leading)
.fixedSize(horizontal: false, vertical: true)
// .frame(width: 300)
TextField("Enter your answer here:", text: $qItem.answer)
.border(.red)
}
}
}
}
.tabViewStyle(.page(indexDisplayMode: .always))
.indexViewStyle(.page(backgroundDisplayMode: .always))
}
}
}
struct QuestionItem: Codable, Identifiable { // <-- here note the struct
var id: Int
var text: String
var type: Int
var answer: String
}