Missing parameter but need parameter to be changed based on user input - ios

Question

This file is for the main structure of the application. This is where the error is coming from which is "Missing argument for parameter 'numberOfDoors' in call". This is because it wants me to add
ContentView(numberOfDoors: <#Int#>)
but im having trouble finding out how I can get what the user chooses to be the int instead of me putting a number in there statically.
import SwiftUI
#main
struct NumOfDoorsApp: App {
var body: some Scene {
WindowGroup {
ContentView()
}
}
}
This is my project file.
import SwiftUI
struct ContentView: View {
#State var numberOfDoors: Int
#State var multiOptions: Array<String>
init(numberOfDoors: Int) {
self.numberOfDoors = numberOfDoors
self.multiOptions = [String](repeating: "", count: numberOfDoors)
}
var body: some View {
NavigationView {
Form{
Section {
Picker("Number of doors", selection: $numberOfDoors) {
ForEach(1 ..< 64) {
Text("\($0) doors")
}
}
ForEach(multiOptions.indices, id: \.self) { index in
TextField("Enter your option...", text: $multiOptions[index])
.padding()
.textFieldStyle(RoundedBorderTextFieldStyle())
}
}
Section {
Text("\(numberOfDoors + 1)")
}
}
}
}
}

Answer 1

One of the most important parts of SwiftUI programming is creating an appropriate model for your views.
#State properties are OK for local, often independent properties, but they typically aren't a good solution for your main data model or where a model needs to be manipulated by the user.
In your case you want the size of the array to change based on the selected number of doors, so you need somewhere for that procedural code to live; The model is that place.
Here is a simple model object you can use
class DoorModel: ObservableObject {
#Published var numberOfDoors: Int {
didSet {
self.adjustArray(newSize: numberOfDoors)
}
}
#Published var doors:[String]
init(numberOfDoors: Int) {
self.numberOfDoors = numberOfDoors
self.doors = [String](repeating: "", count: numberOfDoors)
}
private func adjustArray(newSize: Int) {
let delta = newSize - doors.count
print("new size = \(newSize) Delta = \(delta)")
if delta > 0 {
doors.append(contentsOf:[String](repeating: "", count: delta))
} else if delta < 0 {
doors.removeLast(-delta)
}
}
}
Note that you still need to supply a starting number of doors via the initialiser for your model. Whenever that value changes, the didSet property observer calls a function to add or remove elements from the end of the array.
You can use this model in your view with an #StateObject decorator. This ensures that a single instance is created and reused as your view is redrawn
struct ContentView: View {
#StateObject var model = DoorModel(numberOfDoors: 1)
var body: some View {
NavigationView {
Form{
Section {
Picker("Number of doors", selection: $model.numberOfDoors) {
ForEach(1 ..< 64) { index in
Text("\(index) doors").tag(index)
}
}
ForEach($model.doors.indices, id: \.self) { index in
TextField("Enter your option...", text: $model.doors[index])
.padding()
.textFieldStyle(RoundedBorderTextFieldStyle())
}
}
}
}
}
}
I added the .tag modifier to ensure that the picker works correctly with your 1-based list; By default the tag will be 0 based.

Answer 2

There are, to my opinion, two issues with your code.
Don't initialize ContentView with a parameter. Especially, since you want to start with a value of 0 doors and let the user choose how many doors.
You can't initialize an #State value directly like: self.numberOfDoors = numberOfDoors.
I suggest the following code, it worked for me.
import SwiftUI
struct ContentView: View {
#State private var numberOfDoors: Int
#State private var multiOptions: Array<String>
init() {
_numberOfDoors = State(wrappedValue: 0)
_multiOptions = State(wrappedValue: [String](repeating: "", count: 1))
}
var body: some View {
NavigationView {
Form{
Section {
Picker("Number of doors", selection: $numberOfDoors) {
ForEach(1 ..< 64) {
Text("\($0) doors")
}
}
ForEach(multiOptions.indices, id: \.self) { index in
TextField("Enter your option...", text: $multiOptions[index])
.padding()
.textFieldStyle(RoundedBorderTextFieldStyle())
}
}
Section {
Text("\(numberOfDoors + 1)")
}
}
}
}
}
The issue is, that when you initialize ContentView, the #State or #StateObject variables don't yet exist. You first need to initialize the View, before you can assign an #State variable.
An #State variable is wrapped in a property wrapper, where the original variable at initialization is _variable. Therefore, you need to initialize an #State variable like this:
_myVariable = State(wrappedValue: myContent)
If you don't so it is like this, you get the error as you mentioned.