Question

在我的应用程序中，我正在尝试支持UIButton，我只是想要打印“这是一个测试”当我按下按钮时它会执行经典按钮动画，但是控制台中没有打印任何内容。

var tbutton: UIButton = {
    let button = UIButton(type: .system)
    button.frame = CGRect(x: 40.0, y:400.0, width: 300.0, height: 300.0)
    let image = UIImage(named: "backb")
    button.setBackgroundImage(image, for: .normal)
    button.addTarget(self, action: #selector(dothings), for: .touchUpInside)
    return button
}()

@objc func dothings(){
    print("this is a test")

}

然后我将按钮添加到视图中：

view.addSubview(tbutton)

我是否缺少一段代码，或者我编写了错误的代码？

Answer 1

你不应该以这种方式初始化你的按钮。

从Setting a Default Property Value with a Closure or Function引用Apple文档：

如果使用闭包来初始化属性，请记住在执行闭包时尚未初始化实例的其余部分。这意味着您无法从闭包中访问任何其他属性值，即使这些属性具有默认值也是如此。此外：

您也不能使用隐式自身属性，也不能调用任何实例的方法，因此问题在于：

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所以为了解决这个问题，你应该在ViewController完全初始化之后移动按钮初始化（或移动addTarget）（例如：button.addTarget(self, action: #selector(dothings), for: .touchUpInside)）。

另一种解决问题的方法，假设您仅在viewDidLoad之后使用此类按钮，则将其定义为viewDidLoad：

惰性存储属性是一个属性，其初始值在第一次使用之前不会计算

Swift4：UIButton无法正常工作

1 个答案: