SwiftUI: Why doesn't ObservedObject work in AppDelegate?

Question

I've tried the example from the ObservableObject documentation.

class Contact: ObservableObject {
    @Published var name: String = "me"
    @Published var age: Int = 7
}

When I make a Swift Playground with the code:

let c = Contact()
c.objectWillChange.sink { print("This prints") }
c.age += 1

objectWillChange triggers and the line prints.

So far so good.

I now make a View in SwiftUI:

struct ContentView: View {
    @ObservedObject var contact = Contact
    ...

I create this View in the AppDelegate, and do:

   contentView.contact.objectWillChange.sink { print("This doesn't print.") }

I've connected the contact to various controls, and changing any fields updates all the controls. Doing onReceive(contact.objectWillChange) also works fine. But not connecting to it in the AppDelegate. I've tried logging deinit() to make sure we're talking about the same object. I've tried using ImmediateScheduler. No dice. Why is this not working?

Why did you create a View in the appDelegate in the first place? — Mojtaba Hosseini, Oct 17 '19 at 09:01
On macOS, new project creates a `NSWindow` and sets the `contentView` to `NSHostingView(rootView: ContentView())` — neb, Oct 17 '19 at 10:06
Even doing it in `ContentView.swift` does not work, if I do it in the constructor or some such thing. — neb, Oct 17 '19 at 10:09

score 2 · Accepted Answer · answered Oct 17 '19 at 11:36

2

When you create a subscription with .sink you have to save the AnyCancellable object returned

let cancellable = publisher.sink { ... }

And if you assign it to a variable, make sure it is not short lived. As soon as the cancellable object gets deallocated, the subscription will get cancelled too.

answered Oct 17 '19 at 11:36

Sorin Lica

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Thank you, that's it! It even tried to warn me that I ignored the return value from `sink()`, but I was too cool for school... – neb Oct 17 '19 at 13:14

SwiftUI: Why doesn't ObservedObject work in AppDelegate?

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