fail_to_extend_objc_life.md

Using the following method does not hold the object.

method 1:

import UIKit

class SomeViewController: UIViewController {
    
    let value = "something"
    
    deinit {
        print("Test: deinit")
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesEnded(touches, with: event)
        
        dismiss(animated: true) {
            print("Test: dismiss ended")
            
            DispatchQueue.main.asyncAfter(deadline: .now() + 2) { [weak self] in
                guard let sself = self else { return }
                print("Test: then delayed 2s, \(sself.value)")
            }
        }
    }
}

class MainViewController: UIViewController {
    
    @objc func onAction(_ sender: Any) {
        present(SomeViewController(), animated: true, completion: nil)
    }
}

print:

Test: dismiss ended

Test: deinit

method 2:

import UIKit

class SomeViewController: UIViewController {
    
    let value = "something"
    
    deinit {
        print("Test: deinit")
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesEnded(touches, with: event)
        
        dismiss(animated: true) {
            print("Test: dismiss ended")
            
            DispatchQueue.main.asyncAfter(deadline: .now() + 2) { [weak self] in
                withExtendedLifetime(self) {
                    print("Test: then delayed 2s, \(self?.value ?? "nothing")")
                }
            }
        }
    }
}

class MainViewController: UIViewController {
    
    @objc func onAction(_ sender: Any) {
        present(SomeViewController(), animated: true, completion: nil)
    }
}

print:

Test: dismiss ended

Test: deinit

Can only make it work by removing weak keyword.

import UIKit

class SomeViewController: UIViewController {
    
    let value = "something"
    
    deinit {
        print("Test: deinit")
    }

    override func touchesEnded(_ touches: Set<UITouch>, with event: UIEvent?) {
        super.touchesEnded(touches, with: event)
        
        dismiss(animated: true) {
            print("Test: dismiss ended")
            
            DispatchQueue.main.asyncAfter(deadline: .now() + 2) {
                withExtendedLifetime(self) {
                    print("Test: then delayed 2s, \(self.value)")
                }
            }
        }
    }
}

class MainViewController: UIViewController {
    
    @objc func onAction(_ sender: Any) {
        present(SomeViewController(), animated: true, completion: nil)
    }
}

print:

Test: dismiss ended

Test: then delayed 2s, something

Test: deinit