Swift: Can't change class attribute from #objc function - objective-c

Question

I'm trying to capture ProximitySensor activity on SwiftUI.
So I've created a class ProximityOberver and trying to update the attribute 'state' in the notification:
import SwiftUI
import UIKit
class ProximityObserver {
#State var state = false;
#objc func didChange(notification: NSNotification) {
print("MyView::ProximityObserver.didChange")
if let device = notification.object as? UIDevice {
print(device.proximityState)
state = device.proximityState
print(state)
}
}
}
struct ContentView: View {
#State var proximityObserver = ProximityObserver()
func activateProximitySensor() {
print("MyView::activateProximitySensor")
if !UIDevice.current.isProximityMonitoringEnabled {
UIDevice.current.isProximityMonitoringEnabled = true
if UIDevice.current.isProximityMonitoringEnabled {
NotificationCenter.default.addObserver(proximityObserver, selector: #selector(proximityObserver.didChange), name: UIDevice.proximityStateDidChangeNotification, object: UIDevice.current)
}
}
}
func deactivateProximitySensor() {
print("MyView::deactivateProximitySensor")
UIDevice.current.isProximityMonitoringEnabled = false
NotificationCenter.default.removeObserver(proximityObserver, name: UIDevice.proximityStateDidChangeNotification, object: UIDevice.current)
}
var body: some View {
Text(proximityObserver.state ? "true" : "false" )
.animation(.linear(duration: 20).delay(20), value: proximityObserver.state)
.onAppear() {
self.activateProximitySensor()
}
.onDisappear() {
self.deactivateProximitySensor()
}
}
}
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
But even 'state = device.proximityState' code executed, the following print(state) shows the attribute never changed.
MyView::ProximityObserver.didChange
true
false
Can someone explain why this happens, and how to fix this?

Answer 1

Thank you for the comment.
I could fix this as suggested.
class ProximityObserver: ObservableObject {
#Published var state = false;
#objc func didChange(notification: NSNotification) {
print("MyView::ProximityObserver.didChange")
if let device = notification.object as? UIDevice {
print(device.proximityState)
self.state = device.proximityState
print(state, device.proximityState)
}
}
}
struct ContentView: View {
#ObservedObject var proximityObserver = ProximityObserver()
...