swift - slider 在 iPhone 上使程序崩溃，但在模拟器上运行

Question

我使用此代码来跟踪和更新 slider 值，然后转换为字符串并显示在标签上。问题是，此代码在模拟器上有效，但在实际手机上崩溃了。出现错误“解包可选值时意外发现 nil”。我不知道是什么原因导致这种情况，任何帮助将不胜感激。

func updateSlider () {

    sliderBar.value = Float(CMTimeGetSeconds(self.audioPlayer.currentItem!.currentTime()))
    let currentTime = Int((CMTimeGetSeconds(self.audioPlayer.currentItem!.currentTime())))
    let duration = Int((CMTimeGetSeconds(self.audioPlayer.currentItem!.asset.duration)))
    //let total = currentTime - duration

    let minutes = currentTime/60
    let seconds = currentTime - minutes * 60

    let minutes2 = duration/60
    let seconds2 = duration - minutes2 * 60

    self.lblPastTime.text = NSString(format: " %02d:%02d / %02d:%02d  ",minutes2,seconds2, minutes,seconds) as String

}

Answer 1

避免强制展开变量是避免此类错误的好方法:

func updateSlider () {

    guard let currentItem = self.audioPlayer.currentItem else { return }
    sliderBar.value = Float(CMTimeGetSeconds(currentItem.currentTime()))
    let currentTime = Int((CMTimeGetSeconds(currentItem.currentTime())))
    let duration = Int((CMTimeGetSeconds(currentItem.asset.duration)))
    //let total = currentTime - duration

    let minutes = currentTime/60
    let seconds = currentTime - minutes * 60

    let minutes2 = duration/60
    let seconds2 = duration - minutes2 * 60

    self.lblPastTime.text = NSString(format: " %02d:%02d / %02d:%02d  ",minutes2,seconds2, minutes,seconds) as? String

}

使用 guard let 我安全地解开变量，因此如果它为 nil，函数就会返回。