Combine: Problem when replace addObserver with Notification publisher - combine

Question

i try to replace the addObserver method with Notification publisher
But i cant make it work , hope someone can help
i try to setup the publisher under viewDidLoad and receive notification from another swiftui . Since i cant make it work ,So I make it under viewWillAppear within the same swift file for debugging . In the below coding , I can only receive it from the old school method and the method from viewWillAppear not from the viewDidLoad . The setup in viewDidLoad not working and if i miss out let temp2 = under viewWillAppear , it didnt work too . Is that a bugs for combine?
Result is
BBBB
CCCC
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(forName: .dismissSwiftUI, object: nil, queue: .main) { (_) in
print("BBBB")
}
let abc = NotificationCenter.default.publisher(for: .dismissSwiftUI).sink { (_) in
print("AAAA")
}
}
override func viewWillAppear(_ animated: Bool) {
super.viewWillAppear(animated)
// self.checkIfProfitSetup()
let temp2 = NotificationCenter.default.addObserver(forName: .dismissSwiftUI, object: nil, queue: .main) { (_) in
print("CCCC")
}
NotificationCenter.default.post(name: .dismissSwiftUI ,object: nil)
}

Answer 1

The .sink operator returns an AnyCancellable. So your abc property is an AnyCancellable.
The AnyCancellable documentation says
An AnyCancellable instance automatically calls cancel() when deinitialized.
Since abc is a local property, it is deinitialized when viewDidLoad returns. So your subscription is cancelled when viewDidLoad returns.
You need to store the AnyCancellable in an instance property so that it survives. Cancellable defines a store method that helps.
I usually call them “tickets” in my code, because “cancellable” is too verbose. Thus:
private var tickets: [AnyCancellable] = []
override func viewDidLoad() {
super.viewDidLoad()
NotificationCenter.default.addObserver(forName: .dismissSwiftUI, object: nil, queue: .main) { (_) in
print("BBBB")
}
NotificationCenter.default.publisher(for: .dismissSwiftUI)
.sink { _ in print("AAAA") }
.store(in: &tickets)
}