在计时器上创建while循环（swift3）

Question

The code below when compiled is completed instantly. I would like the counter to add 1 every second. So the program should run for 556 seconds. Every second goes by the counter increase by 1.

      var counter = 0

    while true {

        counter += 1

        print(counter)

        if counter == 556 {
            break
        }
    }

Answer 1

Nothing in your code causes it to do one step per second.

The Timer class is perfect for this.

If you only need to support iOS 10.0 and later, the new block-based timer method scheduledTimer(withTimeInterval:repeats:block:) is a good choice.

var counter = 0
weak var timer: Timer?

timer = Timer.scheduledTimer(withTimeInterval: 1.0,
  repeats: true) {
  theTimer in
  counter += 1
  print(counter)
  if counter == 10 {
    print("Counter = 10. theTimer = \(theTimer)")
    theTimer.invalidate()
  }
}

If you need to support older versions of iOS then you'll need to use the version that uses a selector to call an instance method: scheduledTimer(timeInterval:target:selector:userInfo:repeats:)