swift - 这个语句在 Swift 中总是计算为 nil 吗？

Question

open var buttonInit: ((_ index: Int) -> UIButton?)?
...
if let button: UIButton = self.buttonInit?(i) {
    finButton = button
}else {
        let button = UIButton(type: .custom)
        button.setTitleColor(button.tintColor, for: [])
        button.layer.borderColor = button.tintColor.cgColor
        button.layer.borderWidth = 1
        button.layer.cornerRadius = buttonHeight/2
        finButton = button
}

我在AZDialogViewController 中没有找到任何关于buttonInit 的函数描述| .这是否意味着 button: UIButton = self.buttonInit?(i) 将始终为 nil 而 finButton = button 将不会被执行？

Answer 1

你引用的后半部分代码在setUpButton方法中:

fileprivate func setupButton(index i:Int) -> UIButton{
    if buttonHeight == 0 {buttonHeight = CGFloat(Int(deviceHeight * 0.07))}

    let finButton: UIButton

    if let button: UIButton = self.buttonInit?(i) {
        finButton = button
    }else {
        let button = UIButton(type: .custom)
        button.setTitleColor(button.tintColor, for: [])
        button.layer.borderColor = button.tintColor.cgColor
        button.layer.borderWidth = 1
        button.layer.cornerRadius = buttonHeight/2
        finButton = button
    }

这个方法在这里调用:

open func addAction(_ action: AZDialogAction){
    actions.append(action)

    if buttonsStackView != nil{
        let button = setupButton(index: actions.count-1)
        self.buttonsStackView.addArrangedSubview(button)
        //button.frame = buttonsStackView.bounds
        button.center = CGPoint(x: buttonsStackView.bounds.midX,y: buttonsStackView.bounds.maxY)
        animateStackView()
    }
}

从这里我们可以看出，buttonInit 似乎是用来让库的用户指定他们想要什么样的按钮作为操作按钮。另一个证据是 buttonInit 被声明为 open，因此很可能是客户端代码应该设置它，而不是 AZDialogViewController .

此外，README文件显示了这种用法:

Use custom UIButton sub-class:

dialog.buttonInit = { index in
    //set a custom button only for the first index
    return index == 0 ? HighlightableButton() : nil
}

所以为了回答您的问题，如果您设置buttonInit，if 分支将被执行。