Deinit / Invalidate Timer

Question

I'm trying to deinit/invalidate Timer when user press back button but not when he push to next ViewController.

var timer = Timer()
                timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(timePrinter), userInfo: nil, repeats: true)
                timer.fire()

override func viewWillDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
    if self.isMovingFromParentViewController{
        timer.invalidate()
    }
}

It is not working when user press back button.

Answer 1

When you use a scheduled timer with 'target/selector', it retains its target. More specifically, the Runloop retains scheduled timers, in turn which retain their target.

I use this version, which doesn't retain self:

Timer.scheduledTimer(withTimeInterval: 1, repeats: true, block: { [weak self] _ in
    self?.doSomethingRegularly()
})

And you'll still need to invalidate the above timer in your deinit as well, otherwise you'll leak the timer (but not your class).

Answer 2

Don't put the timer invalidate in viewWillDisappear(_:) . Create a deinit method and put it there. When you press the back button the current view controller should be released and the deinit method will fire.

deinit {
  timer.invalidate()
}

Answer 3

Fixed it by adding Timer() in viewDidAppear and on viewDidDisappear I'm doing timer.invalidate()

override func viewDidAppear(_ animated: Bool) {
    if setTimer == true{
        timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(timePrinter), userInfo: nil, repeats: true)
        timer.fire()
    }
}

override func viewDidDisappear(_ animated: Bool) {
    super.viewDidDisappear(animated)
        timer.invalidate()
}