Question

我创建了一个包含2个图片视图的自定义视图，我希望能够从一个到另一个设置动画，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，我收到了错误：使用未解析的标识符。

如何正确访问firstImageView和secondImageView？

Answer 1

您必须使用两个属性：

var firstImageView: UIImageView!
var secondImageView: UIImageView!

目前你在init的本地范围内有两个UIImageView，所以你不能在另一个类方法中使用它，而只是在init范围内。

所以：

class FlashCard: UIView {

    var firstImageView: UIImageView!
    var secondImageView: UIImageView!

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

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

        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)
    }
}

Answer 2

图像视图不需要是任何变量的变量。

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)
    }
}

必须在调用超级初始化器之前初始化类的属性，这就是为什么另一个答案使用隐式解包的可选变量。

如何访问超类初始化期间定义的属性

2 个答案: