这里有几件事
首先，当你声明 counter 时，它被推断为 Int 类型
var counter = 0
您可以通过添加 .0 或指定其类型来将其声明为双精度：
var counter: NSTimeInternval = 0.0
接下来，您可以使用字符串互操作性来显示字符串中的计数变量，如下所示：
gameTimerLabel.text = "\(counter)"
这是一个使用 NSTimer 作为计数器的示例视图控制器，它以秒为单位：
class ViewController: UIViewController {
// Setup a timer and a counter for use
var timer = NSTimer()
var counter : NSTimeInterval = 0
@IBOutlet weak var label: UILabel!
// Invalidest the timer, resets the counter and udpates the label
@IBAction func resetTimer(sender: AnyObject) {
// Invalidate the timer, reset the label.
self.timer.invalidate()
self.label.text = ""
self.counter = 0
}
// A button that when pressed starts and stops the timer
// There's no pause/resume, so it's invalidated & created again
// But the counter value reamins the same
@IBAction func timerBttnTouched(sender: AnyObject) {
if self.timer.valid {
self.timer.invalidate()
} else {
self.setupTimer()
}
}
// Does the actual counting everytime the timer calls this method
func timerFired() {
self.counter += 1
self.label.text = "\(self.counter)"
}
// Setups a timer, adds it to the run loop and specifies what method should fire when the timer fires
func setupTimer() {
// Setupt the timer, this will call the timerFired method every second
self.timer = NSTimer(
timeInterval: 1,
target: self,
selector: #selector(self.timerFired),
userInfo: nil,
repeats: true)
// Add the timer to the run loop
NSRunLoop.currentRunLoop().addTimer(
self.timer,
forMode: NSDefaultRunLoopMode)
}
}
使用计时器时需要注意的重要一点是，当您需要它们时，它们可能并不总是准确地被调用，这应该根据您在使用计时器时所需的精度来考虑。
正如 cmets 中所讨论的，这里的解决方案是使用计时器来触发比较两个日期并使用 NSDateComponentsFormatter 生成字符串以供显示的方法。初始日期在 viewDidLoad 中生成，但可以在任何地方创建：
class ViewController: UIViewController {
// Setup a timer and a counter for use
var timer = NSTimer()
var counter : NSTimeInterval = 0
var startDate: NSDate?
override func viewDidLoad() {
// Set the initial date
self.startDate = NSDate()
}
@IBOutlet weak var label: UILabel!
// Invalidest the timer, resets the counter and udpates the label
@IBAction func resetTimer(sender: AnyObject) {
// Invalidate the timer, reset the label.
self.timer.invalidate()
self.label.text = ""
self.counter = 0
}
// A button that when pressed starts and stops the timer
// There's no pause/resume, so it's invalidated & created again
// But the counter value reamins the same
@IBAction func timerBttnTouched(sender: AnyObject) {
if self.timer.valid {
self.timer.invalidate()
} else {
self.setupTimer()
}
}
// Does the actual counting everytime the timer calls this method
func timerFired() {
let now = NSDate()
let difference = now.timeIntervalSinceDate(self.startDate!)
// Format the difference for display
// For example, minutes & seconds
let dateComponentsFormatter = NSDateComponentsFormatter()
dateComponentsFormatter.stringFromTimeInterval(difference)
self.label.text = dateComponentsFormatter.stringFromTimeInterval(difference)
}
// Setups a timer, adds it to the run loop and specifies what method should fire when the timer fires
func setupTimer() {
// Setupt the timer, this will call the timerFired method every second
self.timer = NSTimer(
timeInterval: 1,
target: self,
selector: #selector(self.timerFired),
userInfo: nil,
repeats: true)
// Add the timer to the run loop
NSRunLoop.currentRunLoop().addTimer(
self.timer,
forMode: NSDefaultRunLoopMode)
}
}