ios - 无法使用自定义类返回类型覆盖方法

Question

有什么方法可以用来覆盖返回自定义类的方法吗？当我尝试使用自定义类作为返回类型覆盖任何方法时，Xcode 抛出错误

下面是我的代码:

class CustomClass {
  var name = "myName"
}

class Parent: UIViewController {

  override func viewDidLoad() {
    methodWithNoReturn()
    print(methodWithStringAsReturn())
    methodWithCustomClassAsReturn()
  }

}

extension Parent {

  func methodWithNoReturn() { }
  func methodWithStringAsReturn() -> String { return "Parent methodWithReturn" }
  func methodWithCustomClassAsReturn() -> CustomClass {
    return CustomClass()
  }

}


class Child: Parent {

  override func methodWithNoReturn() {
    print("Can override")
  }

  override func methodWithStringAsReturn() -> String {
    print("Cannot override")
    return "Child methodWithReturn"
  }

  override func methodWithCustomClassAsReturn() -> CustomClass {
    return CustomClass()
  }

}

错误是在重写这个方法时:

func methodWithCustomClassAsReturn() -> CustomClass

错误信息:

Declarations from extensions cannot be overridden yet

Answer 1

除了编译器不支持之外没有其他原因。要覆盖父类(super class)扩展中定义的方法，您必须声明它与 ObjC 兼容:

extension Parent {
    func methodWithNoReturn() { }
    func methodWithStringAsReturn() -> String { return "Parent methodWithReturn" }

    @objc func methodWithCustomClassAsReturn() -> CustomClass {
        return CustomClass()
    }   
}

// This means you must also expose CustomClass to ObjC by making it inherit from NSObject
class CustomClass: NSObject { ... }

在不涉及所有 ObjC 困惑的情况下，另一种方法是在 Parent 类(不在扩展内)中定义这些方法:

class Parent: UIViewController {

  override func viewDidLoad() {
    methodWithNoReturn()
    print(methodWithStringAsReturn())
    methodWithCustomClassAsReturn()
  }

  func methodWithNoReturn() { }
  func methodWithStringAsReturn() -> String { return "Parent methodWithReturn" }
  func methodWithCustomClassAsReturn() -> CustomClass {
    return CustomClass()
  }

}