我正在开发一个包含两个UIViews的
Swift(v1.2)项目. MyView和MyViewSubclass.
MyView有一个委托,我想在MyViewSubclass中覆盖它作为一个子协议,类似于UITableViews有一个UITableViewDelegate,它也符合超级UIScrollViewDelegate.
我的第一个想法是覆盖超类属性,但这会导致编译器错误,因为子类不能覆盖具有不同类型的超类属性.
@H_404_6@// Example throws a compiler error. Can't override property with different type class MyView : UIView { weak var delegate : MyViewDelegate? } class MyViewSubclass : MyView { override weak var delegate : MyViewSubclassDelegate? // Compiler error } protocol MyViewDelegate { func someFunc () } protocol MyViewSubclassDelegate : MyViewDelegate { //func someFunc () Edit: redefinition not necessary,thanks @Rob! func someOtherFunc () }我的第二个想法是覆盖委托属性的隐式getter和setter方法.子类可以有一个getter,它接受MyViewSubclassDelegate,并转换为MyViewDelegate协议,因此不需要重写属性本身.
此方法还会导致编译器错误.访问器实际上不能“覆盖”超类方法,因为它们具有不同的方法签名,并且不能仅因为它们的名称与超类设置器冲突而被声明.
@H_404_6@// Example throws a compiler error. Can't declare function with a conflicting name class MyViewSubclass : MyView { func setDelegate ( newValue : MyViewSubclassDelegate ) { // Compiler error super.delegate = newValue as? MyViewDelegate } func getDelegate () -> MyViewSubclassDelegate { // Compiler error return super.delegate as? MyViewSubclassDelegate } }我可以让子类重写超类的getter和setter,并将委托存储在一个单独的子类属性中,这样做有效,但是当它真正需要分配时,子类看起来应该被分配一个MyViewDelegate一个MyViewSubclassDelegate,将来可能会造成严重的混乱.
@H_404_6@// Example works,but it is unclear that MyViewSubclass's delegate should be // assigned a MyViewSubclassDelegate class MyViewSubclass : MyView { private weak var _subclassDelegate : MyViewSubclassDelegate? override weak var delegate : MyViewDelegate? { // Ambiguous type didSet { _subclassDelegate = delegate as? MyViewSubclassDelegate } } }我知道至少类似的东西是可能的,因为像UITableView和UICollectionView这样的类似乎可以做我想要的,但它们也是用Objective-C而不是Swift编写的,所以语言允许的细节可能会有所不同.
有没有办法让Swift子类用子类型覆盖超类的属性？
解决方法
它并不理想,但如果一个协议是从另一个协议继承而不是使用不同的类型,则使用相同的类型,但在didSet中实现验证：
@H_404_6@class MyView : UIView {
/// The `MyViewDelegate` delegate
weak var delegate: MyViewDelegate?
}
class MyViewSubclass: MyView {
/// The `MyViewSubclassDelegate` delegate.
///
/// **Note: This must be MyViewSubclassDelegate**
override weak var delegate: MyViewDelegate? {
didSet {
assert(delegate == nil || delegate is MyViewSubclassDelegate,"The delegate of MyViewSubclass must be of type `MyViewSubclassDelegate`")
}
}
}
它不够优雅,但至少你会立即得到运行时错误,这会将问题引起程序员的注意.通过包含///注释,它也将显示在快速帮助中.
–
或者,您可以采取更激进的更改,例如：类似于ABPeoplePickerNavigationController的delegate和peoplePickerDelegate属性,其中子类委托是通过不同的属性指定的.
