How do I implement data binding in a View Controller in SwiftUI? - ios

Question

I have a UIKit ViewController that's nested inside a SwiftUI view using ViewControllerRepresentable. The SwiftUI view manages a bit of state (an Int, in this example) that I want to display in the UIKit view. When the user taps a button in the SwiftUI parent view, the state change should be reflected in the UIKit view. I've tried using the #Binding property wrapper to keep the two in sync, but clearly I'm missing something, as my view controller's initialiser throws a compile-time error.
I'm quite new to iOS development so perhaps I'm going in the complete wrong direction here. Any help would be greatly appreciated.
The code is as follows (simplified):
struct ContentView: View {
#State private var currentNumber: Int
init(currentNumber: Int) {
self.currentNumber = currentNumber
}
var body: some View {
FancyLabelViewControllerRepresentable(currentNumber: self.$currentNumber)
Button("Increment") {
self.currentNumber += 1
}
}
}
struct FancyLabelViewControllerRepresentable: UIViewControllerRepresentable {
typealias UIViewControllerType = FancyLabelViewController
#Binding var currentNumber: Int
init(currentNumber: Binding<Int>) {
self._currentNumber = currentNumber
}
func makeUIViewController(context: Context) -> FancyLabelViewController {
let fancyLabel = FancyLabelViewController(number: self.currentNumber)
fancyLabel.currentNumberInLabel = self.currentNumber
return fancyLabel
}
func updateUIViewController(_ uiViewController: FancyLabelViewController, context: Context) {
uiViewController.currentNumberInLabel = self.currentNumber
}
}
class FancyLabelViewController: UIViewController {
var label = UILabel()
#Binding var currentNumberInLabel: Int
init(number: Int) {
// Error: 'self' used in property access 'currentNumberInLabel' before 'super.init' call
self.currentNumberInLabel = number
// Error: Property 'self.currentNumberInLabel' not initialized at super.init call
super.init(nibName: nil, bundle: nil)
}
required init(coder: NSCoder) {
fatalError("Not implemented")
}
override func viewDidLoad() {
super.viewDidLoad()
label.text = "\(currentNumberInLabel)"
view = label
}
}

Answer 1

I think you don't need the
#Binding var currentNumberInLabel: Int
because the UIViewControllerRepresentable already takes care of updating the currentNumberInLabel value, but you also needs to update the
label.text = "\(currentNumberInLabel)"
So I did something like
class FancyLabelViewController: UIViewController {
var label = UILabel()
var currentNumberInLabel: Int
init(number: Int) {
self.currentNumberInLabel = number
super.init(nibName: nil, bundle: nil)
}
required init(coder: NSCoder) {
fatalError("Not implemented")
}
override func viewDidLoad() {
super.viewDidLoad()
label.text = "\(currentNumberInLabel)"
view = label
}
func updateLabel() {
label.text = "\(currentNumberInLabel)"
}
}
and call updateLabel from UIViewControllerRepresentable as
func updateUIViewController(_ uiViewController: FancyLabelViewController, context: Context) {
uiViewController.currentNumberInLabel = self.currentNumber
uiViewController.updateLabel()
}