Swift：使用 scheduleTimerWithTimeInterval 调用的额外参数

Question

我创建了一个简单的 WatchApp 节拍器。我将 NSTimer 与 .scheduledTimerWithTimeInterval 一起使用，并且出现错误Extra Argument 'selector' in call

感谢您的回答

func playBeat() {

        if(self.State == true) {
            self.State == false
            [labelPlayPause.setTitle("Pause")]
        } else {
            self.State == true
            [labelPlayPause.setTitle("Play")]
        }

        BPMValue = 10
        var BPMInt:Int = Int(BPMValue)
        let value = "\(BPMInt) BPM"
        labelBPM.setText(value)
        let aSelector: Selector = "playBeat"

        dispatch_async(dispatch_get_main_queue(), {
            NSTimer.scheduledTimerWithTimeInterval(60/self.BPMValue, target:self, selector: aSelector, userInfo:nil, repeats:false)
        })

    }

Answer 1

这是来自 Swift 的糟糕错误消息！

这真正意味着您需要确保每个函数参数的类型与传递的值的类型相匹配。

在您的情况下，BPMValue 是 Float，scheduledTimerWithTimeInterval 是预期的，NSTimeInterval 作为其第一个参数。请注意，NSTimeInterval (Double) 和 Float 不等效。在 Objective-C 中你会得到一个隐式转换，这在 Swift 中不会发生。

试试

NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(60/self.BPMValue), target:self, selector: aSelector, userInfo:nil, repeats:false)

---

附带说明一下，您可以在 Swift 中编写更简洁的代码：

func playBeat() {

    if State {          // If State is a Bool, you can lose the '== true'
        State = false   // Must use set not comparison operator. No need to refer to 'self'.
        labelPlayPause.setTitle("Pause")
    } else {
        State = true  // Must use set not comparison operator.
        labelPlayPause.setTitle("Play")
    }

    BPMValue = 10
    var BPMInt = Int(BPMValue)    // Int Type is inferred
    let value = "\(BPMInt) BPM"
    labelBPM.setText(value)
    let aSelector: Selector = "playBeat"

    dispatch_async(dispatch_get_main_queue(), {
        NSTimer.scheduledTimerWithTimeInterval(NSTimeInterval(60/self.BPMValue), target:self, selector: aSelector, userInfo:nil, repeats:false)
    })

}