I'm trying to understand how Combine works. The following is my sample code.
import UIKit
import Combine
class ViewController: UIViewController {
// MARK: - Variables
var cancellable: AnyCancellable?
// MARK: - IBAction
@IBAction func buttonTapped(_ sender: UIButton) {
currentValueSubject.send(20)
}
// MARK: - Life cycle
var currentValueSubject = CurrentValueSubject<Int, Never>(1)
override func viewDidLoad() {
super.viewDidLoad()
let cancellable = currentValueSubject
.sink { value in
print("New value: \(value)")
}
currentValueSubject.send(5)
currentValueSubject.send(10)
//currentValueSubject.send(completion: .finished)
currentValueSubject.send(15)
//cancellable.cancel()
}
}
If I run it with the iPhone simulator, I get
New value: 1
New value: 5
New value: 10
New value: 15
If I tap the button, the app won't get a new value. I suppose that's because the subscription is cancelled at the end of viewDidLoad? If so, why does it get cancelled? I don't quite see a practical side of Combine's Subject. When is it useful? Thanks.
In your viewDidLoad() you declare a local variable cancellable, which is disposed at the end of the scope. In your case, it is at the end of viewDidLoad.
Please try something like this:
override func viewDidLoad() {
super.viewDidLoad()
self.cancellable = currentValueSubject
.sink { value in
print("New value: \(value)")
}
currentValueSubject.send(5)
currentValueSubject.send(10)
//currentValueSubject.send(completion: .finished)
currentValueSubject.send(15)
//cancellable.cancel()
}
