Swift Playground 中的 NSTimer.scheduledTimerWithTimeInterval [英] NSTimer.scheduledTimerWithTimeInterval in Swift Playground

问题描述

我看到的所有在 Swift 中使用NSTimer.scheduledTimerWithTimeInterval"的例子都使用了target: self"参数，但不幸的是，这不能直接在 Swift Playgrounds 中工作.

All the examples I've seen on using the "NSTimer.scheduledTimerWithTimeInterval" within Swift show using the "target: self" parameter, but unfortunately this doesn't work in Swift Playgrounds directly.

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

这是上面引用的导致错误的示例:

Here's an example referenced above that results in the error:

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()

推荐答案

这些天你真的不应该使用 NSTimer.它会消耗大量资源，导致不必要的电池消耗，并且 API 会导致代码丑陋.

You really should not be using NSTimer these days. It's consumes a lot of resources, causes unnecessary battery drain, and the API lends itself to ugly code.

使用 dispatch_after() 代替:

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

当然，由于计时器会在操场完成后触发，因此您需要等效于 timer.fire() 来强制代码立即执行，而不是在 0 秒延迟后执行.这是它的工作原理:

Of course, since the timer will fire after playground does it's stuff you will need an equivalent of timer.fire() to force the code to execute immediately instead of after a 0 second delay. Here's how that works:

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

dispatch_after(0, dispatch_get_main_queue(), printFrom1To1000)

printFrom1To1000()

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