ios - 如何防止索引越界崩溃？

Question

我正在构建一个原型(prototype)播放器应用程序，它允许我向前和向后跳跃。问题是当我跳到很远或点击上一个按钮多次时应用程序崩溃，因为“索引超出范围”。我尝试了很多东西，但无法解决这个问题。这是我的代码。谢谢!

let player = AVPlayer()

var urlPlayerItems = [String]()

var currentTrack: Int = 0

    @IBAction func didTapPreviousButton(_ sender: UIButton) {
    if (currentTrack - 1) < 0 {
        currentTrack = (urlPlayerItems.count - 1) < 0 ? 0 : (urlPlayerItems.count - 1)
    } else {
        currentTrack -= 1
    }

    playTrack()

}



@IBAction func didTapNextButton(_ sender: UIButton) {
    if (currentTrack + 1) > urlPlayerItems.count {
        currentTrack = 0
    } else {
        currentTrack += 1
    }

    playTrack()
}

Answer 1

let player = AVPlayer()

var urlPlayerItems = [String]()

var currentTrack: Int = 0

@IBAction func didTapPreviousButton(_ sender: UIButton) {
    if currentTrack >= 1 {
        currentTrack -= 1
    }

    playTrack()
}

@IBAction func didTapNextButton(_ sender: UIButton) {
    if currentTrack <= urlPlayerItems.count - 2 {
        currentTrack += 1
    }

    playTrack()
}