ios - 无法覆盖 Swift 中的委托(delegate)属性

Question

我正在尝试制作一个类似于 ImagePickerController 的 StudentPickerController:

class StudentPickerController: UINavigationController, NSCoding {
    unowned(unsafe) var delegate: protocol<StudentPickerControllerDelegate, UINavigationControllerDelegate>?
}

@objc protocol StudentPickerControllerDelegate: NSObjectProtocol {
    optional func studentPickerControllerDidFinishPickingStudent(student: Student)
    optional func studentPickerControllerDidCancel()
}

然而，这给了我:

`Property 'delegate' with the type 'protocol<StudentPickerControllerDelegate, UINavigationControllerDelegate>?' cannot override a property with type 'UINavigationControllerDelegate?'`

当查看 UIImagePickerController 的 swift 文件时，您可以看到:

class UIImagePickerController : UINavigationController, NSCoding {    
    unowned(unsafe) var delegate: protocol<UIImagePickerControllerDelegate, UINavigationControllerDelegate>?
}

protocol UIImagePickerControllerDelegate : NSObjectProtocol {
    optional func imagePickerController(picker: UIImagePickerController, didFinishPickingMediaWithInfo info: [NSObject : AnyObject])
    optional func imagePickerControllerDidCancel(picker: UIImagePickerController)
}

UIImagePickerController 如何能够覆盖 delegate 但我的类不能？

我知道我可以简单地重命名我的属性来避免这种情况，但我想知道 UIImagePickerController 是如何实现这一点的。

Answer 1

So my question is how is ImagePickerController able to override delegate but my class is not?

UIImagePickerController 从 Objective-C 桥接而来，可以覆盖属性。因此，如果您真的非常需要它，那么您可能希望在 Objective-C 中实现 StudentPickerController 并在 Swift 代码中使用它的桥接版本。

如果留在 Swift 中，你可以做的是:

class StudentPickerController: UINavigationController {
    private var studentDelegate: StudentPickerControllerDelegate?
    override var delegate: UINavigationControllerDelegate? {
        didSet { studentDelegate = delegate as? StudentPickerControllerDelegate }
    }
}