Trying to change a value inside a for in loop - ios

Question

I am trying to change a value inside a for in loop. The value Is a bool that I declared as a var and not a let but I get the error "Cannot use mutating member on immutable value: 'notat' is a 'let' constant"
So im trying to make it so that when I tap the image inside the button in my list it will change the completed (bool) value to true. And I want it so that when completed == true I get a filled checkmark
import SwiftUI
struct Notat : Identifiable
{
let id = UUID()
var cost: Int
var name: String
var completed: Bool
}
struct ContentView: View {
var modelData: [Notat] =
[Notat(cost: 50, name: "Klippe plenen", completed: false),
Notat(cost: 100, name: "Vaske speil", completed: true),
Notat(cost: 150, name: "Støvsuge huset", completed: false),
Notat(cost: 50, name: "Vaske bilen", completed: true)]
var body: some View {
List(modelData)
{
notat in HStack
{
Text("\(notat.cost)kr").frame(width: 50, height: 10, alignment: .leading)
Text(notat.name)
Button(action: /*#START_MENU_TOKEN#*/{}/*#END_MENU_TOKEN#*/)
{
Image(systemName: checkmarkSymbol(completed: notat.completed)).font(Font.system(size: 25, weight: .light))
.onTapGesture
{
test(notat: notat)
}
}.frame(maxWidth: .infinity, alignment: .trailing)
}
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
func checkmarkSymbol(completed: Bool) -> String
{
if(completed)
{
return "checkmark.square.fill"
}else
{
return "checkmark.square"
}
}
func test(notat: Notat)
{
notat.completed.toggle() //Here is the error "Cannot use mutating member on immutable value: 'notat' is a 'let' constant"
}

Answer 1

You could do something like the following:
import SwiftUI
struct Notat : Identifiable, Equatable {
let id = UUID()
var cost: Int
var name: String
var completed: Bool
}
//You should change the name to something more descriptive than ViewModel...
class ViewModel: ObservableObject {
#Published var modelData = [
Notat(cost: 50, name: "Klippe plenen", completed: false),
Notat(cost: 100, name: "Vaske speil", completed: true),
Notat(cost: 150, name: "Støvsuge huset", completed: false),
Notat(cost: 50, name: "Vaske bilen", completed: true)
]
func setCompleted(for notat: Notat) {
guard let index = modelData.firstIndex(of: notat) else { return }
modelData[index].completed.toggle()
}
}
struct ContentView: View {
#ObservedObject var viewModel = ViewModel()
var body: some View {
List(viewModel.modelData) { notat in HStack {
Text("\(notat.cost)kr").frame(width: 50, height: 10, alignment: .leading)
Text(notat.name)
Button(action: {})
{
Image(systemName: self.checkmarkSymbol(completed: notat.completed))
.font(Font.system(size: 25, weight: .light))
.onTapGesture
{
self.viewModel.setCompleted(for: notat)
}
}.frame(maxWidth: .infinity, alignment: .trailing)
}
}
}
func checkmarkSymbol(completed: Bool) -> String {
if (completed) {
return "checkmark.square.fill"
}
else {
return "checkmark.square"
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
So basically each time you are tapping on an image, the ViewModel will toggle the completed property and since modelData is marked with #Publish these changes will causing the View to reload itself.
Here it's descriped in more detail...