required 引发的小小思考

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原创：转载请注明出处

首先，因为遇到问题如下：

class MainTabBar: UITabBar {

    override init(frame: CGRect) {

        super.init(frame: frame)

        self.translucent = false

        self.backgroundImage = UIImage(named: "tabbar")

    }

//    //在子类重写父类的必要构造器时，必须在子类的构造器前也添加required修饰符，表明该构造器要求也应用于继承链后面的子类。

    required init?(coder aDecoder: NSCoder) {

        super.init(coder: aDecoder)

    }

}

继承关系链：

UITabBar -> UIView -> 

public class UIView : UIResponder, NSCoding, UIAppearance, UIAppearanceContainer, UIDynamicItem, UITraitEnvironment, UICoordinateSpace, UIFocusEnvironment 

好，在UITabBar、UIView 中init方法并没有显示写出  Required

原因在此：

If you override any of a class‘s designated initializers, you don‘t inherit any other designated initializers. But UIView adopts the NSCoding protocol, which requires an init(coder:)initializer. So you must implement that one too:

required init(coder decoder: NSCoder) {
    super.init(coder: decoder)
}

By the way: Xcode 会提示自动补全代码  

参考链接：

1.http://stackoverflow.com/questions/26081287/required-initializer-initcoder-must-be-provided-by-subclass-of-uitablevi

2.https://developer.apple.com/library/ios/documentation/Swift/Conceptual/Swift_Programming_Language/Initialization.html#//apple_ref/doc/uid/TP40014097-CH18-XID_307

required 引发的小小思考

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原文地址：http://www.cnblogs.com/Jenaral/p/5531855.html