SwiftUI .onAppear, only running once - ios

Question

In a SwiftUI app I have code like this:
var body: some View {
VStack {
Spacer()
........
}
.onAppear {
.... I want to have some code here ....
.... to run when the view appears ....
}
}
My problem is that I would like to run some code inside the .onAppear block, so that it gets run when the app appears on screen, after launching or after being in the background for a while. But it seems like this code is only run once at app launch, and never after. Am I missing something? Or should I use a different strategy to get the result I want?

Answer 1

If you're linking against iOS14 then you can take advantage of the new scenePhase concept:
#Environment(\.scenePhase) var scenePhase
Where ever you are the Environment if injecting this property that you can test against three conditions:
switch newPhase {
case .inactive:
print("inactive")
case .active:
print("active")
case .background:
print("background")
}
So, all together:
struct ContentView: View {
#Environment(\.scenePhase) var scenePhase
var body: some View {
Text("Hello, World!")
.onChange(of: scenePhase) { newPhase in
switch newPhase {
case .inactive:
print("inactive")
case .active:
print("active")
case .background:
print("background")
}
}
}
}

Answer 2

You would have to observe the event when the app is entering foreground and publish it using #Published to the ContentView. Here's how:
struct ContentView: View {
#ObservedObject var observer = Observer()
var body: some View {
VStack {
Spacer()
//...
}
.onReceive(self.observer.$enteredForeground) { _ in
print("App entered foreground!") // do stuff here
}
}
}
class Observer: ObservableObject {
#Published var enteredForeground = true
init() {
if #available(iOS 13.0, *) {
NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIScene.willEnterForegroundNotification, object: nil)
} else {
NotificationCenter.default.addObserver(self, selector: #selector(willEnterForeground), name: UIApplication.willEnterForegroundNotification, object: nil)
}
}
#objc func willEnterForeground() {
enteredForeground.toggle()
}
deinit {
NotificationCenter.default.removeObserver(self)
}
}