SwiftUI ObjectBinding won't receive didchange update from bindable object using combine - swift

Question

I'm testing the Combine framework and using BindableObject as a notification hub for passing data among several views in a SwiftUI ContentView.
One of the views is a table. I click on a row and the value is detected in the print checkpoint, so the bindableobject receives the update.
Problem is, the new string is not broadcasted to the receiving end on the ContentView.
I'm new to this.
View controller with a table view .swift (broadcaster):
import SwiftUI
import Combine
final public class NewestString: BindableObject {
public var didChange = PassthroughSubject<NewestString, Never>()
var newstring: String {
didSet {
didChange.send(self)
print("Newstring: \(newstring)") //<-- Change detected
}
}
init(newstring: String) {
self.newstring = newstring
}
public func update() {
didChange.send(self)
print("--Newstring: \(newstring)")
}
}
final class AViewController: UIViewController {
#IBOutlet weak var someTableView: UITableView!
var returnData = NewestString(newstring:"--")
override func viewDidLoad() {
super.viewDidLoad()
}
}
/// [.....] More extensions here
extension AViewController: UITableViewDelegate {
func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
tableView.deselectRow(at: indexPath, animated: true)
let completion = someResults[indexPath.row]
//// [......] More code here
self.returnData.newstring = "Test string" //<--- change caused
}
}
}
Main content View (broadcast destination):
import SwiftUI
import Combine
struct PrimaryButton: View {
var title: String = "DefaultTitle"
var body: some View {
Button(action: { print("tapped") }) {
Text(title)
}
}
}
struct MyMiniView: View {
#State var aTitle: String = "InitialView"
var body: some View {
VStack{
PrimaryButton(title: aTitle)
}
}
}
struct ContentView: View {
#State private var selection = 0
#ObjectBinding var desiredString: NewestString = NewestString(newstring: "Elegir destino") // <-- Expected receiver
var body: some View {
TabbedView(selection: $selection){
ZStack() {
MyMiniView(aTitle: self.desiredString.newstring ?? "--")
// expected end use of the change, that never happens
[...]
}
struct AView: UIViewControllerRepresentable {
typealias UIViewControllerType = AViewController
func makeUIViewController(context: UIViewControllerRepresentableContext<AView>) -> AViewController {
return UIStoryboard(name: "MyStoryboard", bundle: nil).instantiateViewController(identifier: String(describing: AViewController.self)) as! AViewController
}
func updateUIViewController(_ uiViewController: AViewController, context: UIViewControllerRepresentableContext<AView>) {
//
}
It compiles, runs and prints the change, but no update happens to the MyMiniView's PrimaryButton.

Answer 1

I can't find where you are using your instance of AViewController, but the issue comes from the fact that you are using multiple instance of your bindable object NewestString.
The ContentView as an instance of NewestString, which every update will trigger a view reload.
struct ContentView: View {
#State private var selection = 0
// First instance is here
#ObjectBinding var desiredString: NewestString = NewestString(newstring: "Elegir destino") // <-- Expected receiver
}
The second instance of NewestString is in AViewController, which you actually modify. But, as it's not the same instance of NewestString (the one that is actually declared in the content view), modifying it doesn't trigger the view reload.
final class AViewController: UIViewController {
#IBOutlet weak var someTableView: UITableView!
// The second instance is here
var returnData = NewestString(newstring:"--")
}
To solve this, you need to find a way to "forward" the instance of NewestString created inside your your ContentView to the view controller.
Edit: Found a way to pass the instance of the ObjectBinding to the view controller:
When you add your view into the hierarchy using SwiftUI, you need to pass a Binding of the value that you want to access from the view controller:
struct ContentView: View {
#ObjectBinding var desiredString = NewestString(newstring: "Hello")
var body: some View {
VStack {
AView(binding: desiredString[\.newstring])
Text(desiredString.newstring)
}
}
}
The subscript with a key path will produce a Binding of the given property:
protocol BindableObject {
subscript<T>(keyPath: ReferenceWritableKeyPath<Self, T>) -> > Binding<T> { get }
}
In the view controller wrapper (UIViewControllerRepresentable), you need to forward the given Binding to the actual view controller instance.
struct AView: UIViewControllerRepresentable {
typealias UIViewControllerType = AViewController
var binding: Binding<String>
func makeUIViewController(context: UIViewControllerRepresentableContext<AView>) -> AViewController {
let controller = AViewController()
controller.stringBinding = binding // forward the binding object
return controller
}
func updateUIViewController(_ uiViewController: AViewController, context: UIViewControllerRepresentableContext<AView>) {
}
}
And then, in you view controller, you can use the binding to update your value (using the .value property):
final class AViewController: UIViewController {
var stringBinding: Binding<String>!
override func viewDidLoad() {
super.viewDidLoad()
stringBinding.value = "Hello world !!"
}
}
When the view controller's viewDidLoad is called, the desiredString (in ContentView) will be updated to "Hello world !!", just like the displayed text (Text(desiredString.newstring)).