Swift Playground中的NSTimer.scheduledTimerWithTimeInterval

Question

我在Swift中使用"NSTimer.scheduledTimerWithTimeInterval"时看到的所有示例都使用"target:self"参数显示,但不幸的是,这在Swift Playgrounds中不起作用.

Playground execution failed: <EXPR>:42:13: error: use of unresolved
identifier 'self'
  target: self,

以上引用的示例导致错误:

func printFrom1To1000() {
    for counter in 0...1000 {
        var a = counter        
    }
}

var timer = NSTimer.scheduledTimerWithTimeInterval(0,
    target: self,
    selector: Selector("printFrom1To1000"),
    userInfo: nil,
    repeats: false
    )
timer.fire()

Answer 1

NSTimer这些天你真的不应该使用.它消耗了大量资源,导致不必要的电池消耗,而且API会导致丑陋的代码.

dispatch_after()改为使用:

dispatch_after(0, dispatch_get_main_queue()) { () -> Void in
  for counter in 0...1000 {
    var b = counter
  }
}

当然,由于计时器会在游乐场运行后触发,你需要等效的timer.fire()强制代码立即执行,而不是在0秒延迟之后执行.这是如何工作的:

let printFrom1To1000 = { () -> Void in
  for counter in 0...1000 {
    var b = counter
  }
}

dispatch_after(0, dispatch_get_main_queue(), printFrom1To1000)

printFrom1To1000()