Timer

1. Create property in viewcontroller:

var timer = Timer()

2. In ViewDidLoad:

 self.timer = Timer.scheduledTimer(timeInterval: 1.0, target: self, selector: #selector(FirstViewController.tick), userInfo: nil, repeats: true)

//The top means that every 1 second, the function FirstViewController.tick will be repeated

3. Create the function tick, in it, type out what you want to be updated every second, for instance:

TheLabel.text = getCurrentTime()