我正在编写一个音乐应用程序,通过按下屏幕上的所需按钮,用户可以“平滑地”在不同的鼓模式之间切换。 (“平滑地”是指模式将在用户按下按钮之后立即切换到小节)。
我的问题是,我为下一个模式的延迟启动计算的时间延迟略大于预期。我可以通过将时间延迟减少0.1秒来解决,但如果使用与我目前用于测试的速度不同的速度,这可能无法解决。
计算延迟的代码是:
func startClock() {
let aSelector : Selector = "updateClock"
clock = NSTimer.scheduledTimerWithTimeInterval(0.001, target: self, selector: aSelector, userInfo: nil, repeats: true)
startTime = CFAbsoluteTimeGetCurrent()
}
func stopClock() {
clock.invalidate()
}
func updateClock() {
currentTime = CFAbsoluteTimeGetCurrent()
elapsedTime = currentTime - startTime
elapsedBeats = UInt(elapsedTime / audioMeterUpdateInterval)
elapsedMeasures = UInt( Double(elapsedBeats) / Double(beatUnit[patternSelectIdx]) )
requiredMeasures = elapsedMeasures + 1
requiredBeats = requiredMeasures * UInt(beatUnit[patternSelectIdx])
requiredTime = Double(requiredBeats) * audioMeterUpdateInterval
delayTime = requiredTime - elapsedTime - 0.1 // 0.1 sec is chosen ad hoc
}
用于结束鼓模式的其中一个按钮的代码是:
@IBAction func endShort(sender: UIButton) {
fileName = patternSelect + "End1"
if startPlay == true {
play(fileName, numberOfLoops: 0, delaySec: delayTime)
} else {
play(fileName, numberOfLoops: 0, delaySec: 0)
}
playPauseButton.setImage(playImage, forState: UIControlState.Normal)
startPlay = false
}
最后,上面代码调用的函数play
是
func play(fileName: String, numberOfLoops: Int, delaySec: Double){
if delaySec > 0 {
let delayNSec = Double(NSEC_PER_SEC)*delaySec
let dispatchTime = dispatch_time(DISPATCH_TIME_NOW, Int64(delayNSec))
self.ButtonAudioPlayer.numberOfLoops = numberOfLoops
self.ButtonAudioPlayer.volume = 1.0
self.ButtonAudioURL = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource(fileName, ofType: "wav")!)
dispatch_after(dispatchTime, dispatch_get_main_queue(),{
self.ButtonAudioPlayer = try! AVAudioPlayer(contentsOfURL: self.ButtonAudioURL)
self.ButtonAudioPlayer.play()
})
} else {
ButtonAudioPlayer.numberOfLoops = numberOfLoops
ButtonAudioPlayer.volume = 1.0
ButtonAudioURL = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource(fileName, ofType: "wav")!)
ButtonAudioPlayer = try! AVAudioPlayer(contentsOfURL: ButtonAudioURL)
ButtonAudioPlayer.play()
}
}
有替代方法吗?此外,0.1秒是否可以是与按钮动画时间相关的固定延迟,因此始终保持固定并可以修改?谢谢!