ios - 如何在 Swift 中编写通用的 apply() 函数？

Question

有什么方法可以使以下内容在 Swift 3 中正常工作？

 let button = UIButton().apply {
        $0.setImage(UIImage(named: "UserLocation"), for: .normal)
        $0.addTarget(self, action: #selector(focusUserLocation), 
                     for: .touchUpInside)
        $0.translatesAutoresizingMaskIntoConstraints = false
        $0.backgroundColor = UIColor.black.withAlphaComponent(0.5)
        $0.layer.cornerRadius = 5
     }

apply<T>函数应该采用 (T)->Void 类型的闭包, 运行它通过 self进去，然后简单地返回 self .

另一种选择是为此使用运算符，例如“=>”(借用了 Kotlin 和 Xtend 语言的想法)。

尝试扩展 NSObject像这样:

extension NSObject {   
    func apply<T>(_ block: (T)->Void) -> T
    {
        block(self as! T)
        return self as! T
    }
}

但它需要在闭包中显式声明参数类型:

let button = UIButton().apply { (it: UIButton) in
        it.setImage(UIImage(named: "UserLocation"), for: .normal)
        it.addTarget(self, action: #selector(focusUserLocation), 
                     for: .touchUpInside)
        ...

这很不方便，使整个想法不值得付出努力。类型已经在对象创建时指定，应该可以不明确重复。

谢谢!

Answer 1

HasApply 协议(protocol)

首先让我们定义HasApply协议(protocol)

protocol HasApply { }

及相关扩展

extension HasApply {
    func apply(closure:(Self) -> ()) -> Self {
        closure(self)
        return self
    }
}

接下来让 NSObject 符合 HasApply。

extension NSObject: HasApply { }

就是这样

让我们测试一下

let button = UIButton().apply {
    $0.titleLabel?.text = "Tap me"
}

print(button.titleLabel?.text) // Optional("Tap me")

注意事项

I wouldn't use NSObject (it's part of the Objective-C way of doing things and I assume it will be removed at some point in the future). I would prefer something like UIView instead.

extension UIView: HasApply { }