c# - 在基类中定义后，是否需要在派生类中定义相同的接口(interface)？

Question

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Answer 1

好吧，你可能需要这样做；这是一种可能的情况:

克隆时，我们通常希望通过克隆对象类型返回非通用对象:

class Base {
  // We can't declare this method as virtual: Derived class will return Derived 
  public Base Clone() {
    ...
  }
}

...

Base test = new Base();

Base duplicate = test.Clone(); 

如果我们想要实现IClonable，我们必须显式(为了解决Clone()名称冲突):

class Base : ICloneable {
  public Base Clone() {
    ... 
  }

  // This method is efficiently private, and that's why can't be virtual
  object ICloneable.Clone() => Clone();
}

现在我们想要一个也可以被克隆的 Derived 类:

class Derived : Base {
  // Note that now we have new Clone method which returns Derived instance (not Base one)
  public new Derived Clone() {
    ...
  }
}

...

Derived test = new Derived();

Derived duplicate = test.Clone();

如果我们保持这样，那么我们将有错误的行为:

 Derived test = new Derived();

 // This will be wrong: 
 // Base.ICloneable.Clone() will be called which executes "Base Clone()" method
 // instead of expected "new Derived Clone()"
 object clone = (test as IClonable).Clone();

所以我们必须重新实现IClonable接口(interface):

class Derived : Base, ICloneable {
  // Please, note that now we have new Clone method which returns Derived instance
  public new Derived Clone() {
    ...
  }

  // This ICloneable implementation will call Derived Clone()
  object ICloneable.Clone() => Clone();
}

...

// Derived ICloneable.Clone() will be called
// which executes "new Derived Clone()" method
object clone = (test as IClonable).Clone();