Swift - UIButton重写setSelected

问题描述

限时删除！！

我正在Swift中创建一个UIButton子类，以便在选择时执行自定义绘图和动画

I'm making a UIButton subclass in Swift to perform custom drawing and animation on selection

在Swift中覆盖的等价物是什么？ - （void）setSelected：（BOOL）在ObjC中选择？

我试过

覆盖var选择：Bool

所以我可以实现一个观察者，但我得到了

so I could implement an observer but I get

无法覆盖存储的属性'selected'

推荐答案

与其他提到的一样，您可以使用 willSet 来检测更改。但是，在覆盖中，您不需要将值赋值给super，您只需观察现有的更改。

Like others mentioned you can use willSet to detect changes. In an override, however, you do not need assign the value to super, you are just observing the existing change.

您可以在以下操场中观察到几件事：

A couple things you can observe from the following playground:

1. 覆盖的属性willSet / didSet 仍然为<$ c $调用super C>获取/设置。您可以判断，因为状态从 .normal 更改为 .selected 。


2. 即使值未更改，也会调用willSet和didSet，因此您可能希望将 selected 的值与 newValue进行比较 in willSet 或 oldValue in didSet 确定是否要制作动画。

1. Overriding a property for willSet/didSet still calls super for get/set. You can tell because the state changes from .normal to .selected.
2. willSet and didSet are called even when the value is not changing, so you will probably want do the compare the value of selected to either newValue in willSet or oldValue in didSet to determine whether or not to animate.

import UIKit

class MyButton : UIButton {

    override var isSelected: Bool {
        willSet {
            print("changing from \(isSelected) to \(newValue)")
        }

        didSet {
            print("changed from \(oldValue) to \(isSelected)")
        }
    }
}

let button = MyButton()

button.state == .normal
button.isSelected = true // Both events fire on change.
button.state == .selected
button.isSelected = true // Both events still fire.

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