Swift开发求助：实现可恢复图片视图背景色的撤销按钮

• 现有代码逻辑顺序错误：生成新随机色后直接将新色赋值给previousColor变量，导致该变量存储的永远是当前正在显示的颜色，而非上一次生效的颜色，点击撤销无法回到上一步状态。

调整随机按钮点击事件中的赋值顺序，在生成新颜色前先存储当前正在显示的颜色即可：

var previousColor: UIColor?
@IBAction func didPressRandomButton(_ sender: Any) {
    // 先存储当前显示的颜色作为撤销备用
    previousColor = imageDisplay.backgroundColor
    let randomRed = CGFloat.random(in: 0...1)
    let randomGreen = CGFloat.random(in: 0...1)
    let randomBlue = CGFloat.random(in: 0...1)
    let color = UIColor(red: randomRed, green: randomGreen, blue: randomBlue, alpha: 1)
    imageDisplay.backgroundColor = color
}
@IBAction func didPressUndoButton(_ sender: Any) {
    guard let undoColor = previousColor else { return }
    imageDisplay.backgroundColor = undoColor
}

如果需要支持多次点击撤销、依次回溯更早的颜色，可以用数组作为历史栈存储所有过往颜色：

// 颜色历史栈，存储所有生效过的颜色
var colorHistory: [UIColor] = []

@IBAction func didPressRandomButton(_ sender: Any) {
    if let currentColor = imageDisplay.backgroundColor {
        colorHistory.append(currentColor)
    }
    let randomRed = CGFloat.random(in: 0...1)
    let randomGreen = CGFloat.random(in: 0...1)
    let randomBlue = CGFloat.random(in: 0...1)
    let color = UIColor(red: randomRed, green: randomGreen, blue: randomBlue, alpha: 1)
    imageDisplay.backgroundColor = color
}

@IBAction func didPressUndoButton(_ sender: Any) {
    guard !colorHistory.isEmpty else { return }
    let lastColor = colorHistory.removeLast()
    imageDisplay.backgroundColor = lastColor
}

内容的提问来源于stack exchange，提问作者Jon Cina