How to update UIViewRepresentable with ObservableObject - swift

Question

I'm trying to learn Combine with SwiftUI and I'm struggling how to update my view (from UIKit) with ObservableObject (previously BindableObject). The issue is that, obviously, method updateUIView will not fire once the #Published object sends the notification it was changed.
class DataSource: ObservableObject {
#Published var locationCoordinates = [CLLocationCoordinate2D]()
var value: Int = 0
init() {
Timer.scheduledTimer(withTimeInterval: 3, repeats: true) { timer in
self.value += 1
self.locationCoordinates.append(CLLocationCoordinate2D(latitude: 52, longitude: 16+0.1*Double(self.value)))
}
}
}
struct MyView: UIViewRepresentable {
#ObservedObject var dataSource = DataSource()
func makeUIView(context: Context) -> MKMapView {
MKMapView(frame: .zero)
}
func updateUIView(_ view: MKMapView, context: Context) {
let newestCoordinate = dataSource.locationCoordinates.last ?? CLLocationCoordinate2D(latitude: 52, longitude: 16)
let annotation = MKPointAnnotation()
annotation.coordinate = newestCoordinate
annotation.title = "Test #\(dataSource.value)"
view.addAnnotation(annotation)
}
}
How to bind that locationCoordinates array to the view in such a way, that a new point is in fact added each time it refreshes?

Answer 1

To make sure your ObservedObject does not get created multiple times (you only want one copy of it), you can put it outside your UIViewRepresentable:
import SwiftUI
import MapKit
struct ContentView: View {
#ObservedObject var dataSource = DataSource()
var body: some View {
MyView(locationCoordinates: dataSource.locationCoordinates, value: dataSource.value)
}
}
class DataSource: ObservableObject {
#Published var locationCoordinates = [CLLocationCoordinate2D]()
var value: Int = 0
init() {
Timer.scheduledTimer(withTimeInterval: 3, repeats: true) { timer in
self.value += 1
self.locationCoordinates.append(CLLocationCoordinate2D(latitude: 52, longitude: 16+0.1*Double(self.value)))
}
}
}
struct MyView: UIViewRepresentable {
var locationCoordinates: [CLLocationCoordinate2D]
var value: Int
func makeUIView(context: Context) -> MKMapView {
MKMapView(frame: .zero)
}
func updateUIView(_ view: MKMapView, context: Context) {
print("I am being called!")
let newestCoordinate = locationCoordinates.last ?? CLLocationCoordinate2D(latitude: 52, longitude: 16)
let annotation = MKPointAnnotation()
annotation.coordinate = newestCoordinate
annotation.title = "Test #\(value)"
view.addAnnotation(annotation)
}
}

Answer 2

this solution worked for me but with EnvironmentObject https://gist.github.com/svanimpe/152e6539cd371a9ae0cfee42b374d7c4

Answer 3

I'm gonna provide a general solution for any UI/NS view representable using combine. There are performance benefits to my method.
Created an Observable Object and wrap the desired properties with
#Published wrapper
Inject the Observed object via the updateView method in the view
representable using a method you'll make in step 3
Subclass the desired view with the view model as a parameter.
Create an addViewModel method and use
combine operators/ subscribers and add them to cancellable.
Note - Works great with environment objects.
struct swiftUIView : View {
#EnvironmentObject var env : yourViewModel
...
...
UIViewRep(wm : env)
}
struct UIViewRep : UIViewRepresentable {
var wm : yourViewModel
func makeUIView {
let yv = yourView()
yv.addViewModel(wm)
return yv
}}
class yourView : UIView {
var viewModel : yourViewModel?
var cancellable = Set<AnyCancellable>()
...
...
func addViewModel( _ wm : yourViewModel) {
self.viewModel = wm
self.viewModel?.desiredProperty
.sink(receiveValue: { [unowned self] w in
print("Make changes with ", w)
}).store(in: &cancellable)
}
}