快速计时器（以毫秒为单位）

Question

我想每毫秒更改一次计时器，但是它没有按预期工作。

NSTimer.scheduledTimerWithTimeInterval(0.001, target: self, selector: Selector("advanceTimer:"), userInfo: nil, repeats: true);

func advanceTimer(timer: NSTimer){

    self.time += 0.001;

    let milliseconds = self.time * 100;
    let remaingMilliseconds = Int((milliseconds % 1000) / 10);
    let seconds = Int((milliseconds / 1000) % 60)

    let strSeconds = String(format: "%02d", seconds)
    let strFraction = String(format: "%02d", remaingMilliseconds)

    timerText.text = "\(strSeconds):\(strFraction)";

 }

结果是

计时器以毫秒为单位更改为100（00：100），然后更改为01:00 = 40真实秒

邓肯方法：

var time: NSTimeInterval = 0;
var startTime: NSTimeInterval = 0;

//And your  timer method...
func advanceTimer(timer: NSTimer){
    //Total time since timer started, in seconds
    self.time = NSDate.timeIntervalSinceReferenceDate() - startTime
    println(self.time);
    //The rest of your code goes here
}

override func didMoveToView(view: SKView) {

    // Set anchor point
    self.anchorPoint = CGPointMake(0.5, 0.5);


    var startTime: NSTimeInterval
    //Sart the timer
    startTime = NSDate.timeIntervalSinceReferenceDate()
    NSTimer.scheduledTimerWithTimeInterval(0.02,
            target: self,
            selector: Selector("advanceTimer:"),
            userInfo: nil,
            repeats: true)
}

结果：456680125.54539第一次打印

Answer 1

正如Martin在评论中所说，计时器的分辨率为50-100毫秒（0.05至0.1秒）。尝试以短于该间隔的时间运行计时器将无法获得可靠的结果。另外，计时器不是实时的。它们取决于它们所附加的运行循环，并且如果运行循环变得繁忙，则计时器的启动会延迟。

不要在每次触发计时器时尝试增加计数器，而是在启动计时器时记录开始时间，然后做一些数学运算以弄清楚发生了多少时间：

var startTime: NSTimeInterval

//Sart the timer
startTime = NSDate.timeIntervalSinceReferenceDate()
NSTimer.scheduledTimerWithTimeInterval(0.02, 
  target: self, 
  selector: Selector("advanceTimer:"), 
  userInfo: nil,
  repeats: true)


//And your  timer method...
func advanceTimer(timer: NSTimer)
{
  //Total time since timer started, in seconds
  self.time = NSDate.timeIntervalSinceReferenceDate() - startTime
  //The rest of your code goes here
 }

编辑：

此代码的Swift 3版本如下所示：

（写为测试项目中的视图控制器）

class ViewController: UIViewController {

  weak var timer: Timer?
  var startTime: Double = 0
  var time: Double = 0

  @IBOutlet weak var timeValueLabel: UILabel!

  /* 
  When the view controller first appears, record the time and start a timer
  */
  override func viewDidAppear(_ animated: Bool) {
    startTime = Date().timeIntervalSinceReferenceDate
    timer = Timer.scheduledTimer(timeInterval: 0.05,
                                 target: self,
                                 selector: #selector(advanceTimer(timer:)),
                                 userInfo: nil,
                                 repeats: true)
  }

  //When the view controller is about to disappear, invalidate the timer
  override func viewWillDisappear(_ animated: Bool) {
    timer?.invalidate()
  }


  func advanceTimer(timer: Timer) {

    //Total time since timer started, in seconds
    time = Date().timeIntervalSinceReferenceDate - startTime

    //The rest of your code goes here

    //Convert the time to a string with 2 decimal places
    let timeString = String(format: "%.2f", time)

    //Display the time string to a label in our view controller
    timeValueLabel.text = timeString
  }
}