Aim

Understand retain cycle when working with closures in swift

Pre-setup

Follow the steps to setup a alert when a ViewController is deallocated:

• In Xcode, go to the Breakpoint navigator (Cmd+8)
• At the bottom-left on the screen, tap '+', then select "Symbolic Breakpoint..." from the menu
• Fill the form:
  • Name: UIViewController dealloc
  • Symbol: -[UIViewController dealloc]
  • Module: UIKitCore (or leave empty)
  • Condition: !(BOOL)([[$arg1 description] containsString:@"Input"]) to exclude UIInputViewController, UICompatibilityInputViewController, etc.
  • Ignore: leave at zero
  • Action: Select "Log Message"
  • Enter: --- dealloc @(id)[$arg1 description]@ @(id)[$arg1 title]@ (or customize as needed)
  • Select "Log message to console"
  • Next to "Action: Log Message", tap on '+' to add a new Action
  • Select: "Sound" and choose any sound from the list (Submarine, Pop...)
  • Check "Automatically continue after evaluating actions" so Xcode does not stop at the breakpoint

Run the app

• Move onto the second screen, and wait for the callback to be received (check the logs)
• Press the back button. Nothing really happened.
• Now uncomment the code inside lazy var delayViewModel = DelayViewModel and re-run the app.
• Go to the second screen, wait for the callback, and then press back.
• If your Pre-setup was successful, you should hear a sound with the text in the logs:

--- dealloc @"<MemoryManagementTest.CallbackViewController: 0x1032133f0>" 0x0

This means the CallbackViewController was deallocated successfully.