ios - 如何访问父类(super class)初始化期间定义的属性

Question

我正在创建一个带有 2 个 ImageView 的自定义 View ，我希望能够从一个 ImageView 到另一个 ImageView 进行动画处理，这是我的代码:

class FlashCard: UIView {

required init?(coder: NSCoder) {
    super.init(coder: coder)

    let firstImageView = UIImageView(frame: self.frame)
    firstImageView.image = UIImage(named: "Lightning")
    addSubview(firstImageView)

    let secondImageView = UIImageView(frame: frame)
    secondImageView.image = UIImage(named: "Tifa")
    addSubview(secondImageView)
    secondImageView.isHidden = true

}

func showBack() {
    UIView.transition(from: firstImageView, to: secondImageView, duration: 1.0, options: UIViewAnimationOptions.transitionCrossDissolve, completion: nil)
}
}

但是在我的 showBack 函数中，我得到了错误:使用未解析的标识符。

如何正确访问 firstImageView 和 secondImageView？

Answer 1

ImageView 不需要是变量，无论是什么类型的可选。

class FlashCard: UIView {

    let firstImageView = UIImageView()
    let secondImageView: UIImageView()

    required init?(coder: NSCoder) {
        super.init(coder: coder)

        firstImageView.frame = frame
        firstImageView.image = UIImage(named: "Lightning")
        addSubview(firstImageView)

        secondImageView.frame = frame
        secondImageView.image = UIImage(named: "Tifa")
        addSubview(secondImageView)
        secondImageView.isHidden = true
    }

    func showBack() {
        UIView.transition(from: firstImageView, to: secondImageView, duration: 1.0, options: UIViewAnimationOptions.transitionCrossDissolve, completion: nil)
    }
}

类的属性必须在 super 初始化器被调用之前初始化，这就是为什么另一个答案使用隐式展开的可选变量。