SwiftUI .onTapGesture issue in TableView with Sections and Rows - swift

Question

I have two models:
struct Category: Identifiable {
var id = UUID()
var title: String
var number: Int
var items: [ChecklistItem]
}
and:
struct ChecklistItem: Identifiable {
let id = UUID()
var name: String
var isChecked = false
}
with:
class Checklist: ObservableObject {
#Published var items = [Category]()
func deleteListItem(whichElement: IndexSet) {
items.remove(atOffsets: whichElement)
}
func moveListItem(whichElement: IndexSet, destination: Int) {
items.move(fromOffsets: whichElement, toOffset: destination)
}
}
I try to implement tap on row to check and uncheck cheklist item in tableView with sections and rows, but I cannot get how this can be released. My code:
struct ChecklistView: View {
#EnvironmentObject var checklist: Checklist
#State var newChecklistItemViewIsVisible = false
var body: some View {
NavigationView {
List {
ForEach(checklist.items) { category in
Section(header: Text(category.title)) {
ForEach(category.items) { item in
HStack {
Text(item.name)
Spacer()
Text(item.isChecked ? "✅" : "🔲")
}
.background(Color.white)
.onTapGesture {
if let matchingIndex =
category.items.firstIndex(where: { $0.id == item.id }) {
category.items[matchingIndex].isChecked.toggle()
}
}
}
}
}
.onDelete(perform: checklist.deleteListItem)
.onMove(perform: checklist.moveListItem)
}
.navigationBarItems(
leading: Button(action: { self.newChecklistItemViewIsVisible = true }) {
HStack {
Image(systemName: "plus.circle.fill")
Text("Add")
}
},
trailing: EditButton()
)
.navigationBarTitle("List")
}
.sheet(isPresented: $newChecklistItemViewIsVisible) {
NewChecklistItemView(checklist: self.checklist)
}
}
}
I get error with this code on line with category.items[matchingIndex].isChecked.toggle():
Cannot use mutating member on immutable value: 'category' is a 'let' constant
How I can get to ChecklistItem and make it check and uncheck on tap.

Answer 1

import SwiftUI
//Change to class and add NSObject structs are immutable
class Category: NSObject, Identifiable {
let id = UUID()
var title: String
var number: Int
var items: [ChecklistItem]
//Now you need an init
init(title: String , number: Int, items: [ChecklistItem]) {
self.title = title
self.number = number
self.items = items
}
}
//Change to class and add NSObject structs are immutable
class ChecklistItem: Identifiable {
let id = UUID()
var name: String
var isChecked: Bool = false
//Now you need an init
init(name: String) {
self.name = name
}
}
class Checklist: ObservableObject {
#Published var items = [Category]()
}
struct ChecklistView: View {
//Can be an #EnvironmentObject if the #ObservedObject comes from a higher View
#ObservedObject var checklist: Checklist = Checklist()
#State var newChecklistItemViewIsVisible = false
var body: some View {
NavigationView {
List {
ForEach(checklist.items) { category in
Section(header: Text(category.title)) {
ForEach(category.items) { item in
Button(action: {
print(item.isChecked.description)
item.isChecked.toggle()
//Something to trigger the view to refresh will not be necessary if using something like #FetchRequest or after you somehow notify `checklist.items` that there is a change
checklist.objectWillChange.send()
}) {
HStack {
Text(item.name)
Spacer()
Text(item.isChecked ? "✅" : "🔲")
}//HStack
//White is incompatible with Text Color in Dark Mode
.background(Color.gray)
}//Button
}//ForEach
}//Section
}//ForEach
//Methods not provided
//.onDelete(perform: checklist.deleteListItem)
//.onMove(perform: checklist.moveListItem)
}
.navigationBarItems(
leading: Button(action: {
self.newChecklistItemViewIsVisible = true
//Code to Add Samples
checklist.items.append(Category(title: "Test", number: Int.random(in: 0...100), items: [ChecklistItem(name: "Test")]))
}) {
HStack {
Image(systemName: "plus.circle.fill")
Text("Add")
}
},
trailing: EditButton()
)
.navigationBarTitle("List")
}
.sheet(isPresented: $newChecklistItemViewIsVisible) {
//Pass as an #EnvironmentObject
NewChecklistItemView().environmentObject(checklist)
}
}
}
struct NewChecklistItemView: View {
#EnvironmentObject var checklist: Checklist
var body: some View {
Text(checklist.items.count.description)
}
}
struct ChecklistView_Previews: PreviewProvider {
static var previews: some View {
//When the #ObservedObject comes from a higher View remove comment below
ChecklistView()//.environmentObject(Checklist())
}
}

Answer 2

The reason you are getting that error is because structs are immutable. You should use method marked with "mutating" inside desired struct. Something like
if let matchingIndex = category.items.firstIndex(where: { $0.id == item.id }) {
category.items[matchingIndex].toggleItem()
}
and inside your struct:
mutating func toggleItem() {
self.isChecked.toggle()
}
But i would recommend you to use #State instead, because what you are trying to do is straight forward related to how you represent your view. And later, when user is willing to do something with that selection you send that data to your model