Question

假设我有一个父类和子类，如下所示

父类：

class Parent
{
    public string _First;
    public string _Last;

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(obj, null))
            return false;
        else if (ReferenceEquals(obj, this))
            return true;
        else if (obj is Parent == false)
            return false;
        else
            return this.Equals(obj as Parent) & base.Equals(obj);

    }

    public override int GetHashCode()
    {
        unchecked
        {
            return this._First.GetHashCode() ^ this._Last.GetHashCode() ^ base.GetHashCode();
        }
    }

    public bool Equals(Parent that)
    {
        if (ReferenceEquals(that, null))
            return false;
        else if (ReferenceEquals(that, this))
            return true;
        else
            return this._First.Equals(that._First) & this._Last.Equals(that._Last);
    }

    public static  bool operator ==(Parent p1, Parent p2)
    {
        return p1.Equals(p2);
    }

    public static  bool operator !=(Parent p1, Parent p2)
    {
        return !p1.Equals(p2);
    }


}

儿童班：

  class Child : Parent
{
    public string Address;

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(obj, null))
            return false;
        else if (ReferenceEquals(obj, this))
            return true;
        else if (obj is Parent == false)
            return false;
        else
            return this.Equals(obj as Child);

    }

    public override int GetHashCode()
    {
        unchecked
        {
            return this._First.GetHashCode() ^ this._Last.GetHashCode() ^ base.GetHashCode();
        }
    }

    public bool Equals(Child that)
    {
        if (ReferenceEquals(that, null))
            return false;
        else if (ReferenceEquals(that, this))
            return true;
        else
            return this.Address.Equals(that.Address) & base.Equals(that);
    }

    public static  bool operator ==(Child p1,Child p2)
    {
        return p1.Equals(p2);
    }

    public static bool operator !=(Child p1, Child p2)
    {
        return !p1.Equals(p2);
    }

}

以下是比较两个孩子实例的代码。

 Parent p = new Child() { _First = "Mitul", _Last = "Patel", Address="abc1"};
        Parent p1 = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc" };

        Child c = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc1" };
        Child c1 = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc" };

        Console.WriteLine(p.Equals(p1));
        Console.WriteLine(p == p1);

        Console.WriteLine(c.Equals(c1));
        Console.WriteLine(c == c1);

        Console.Read();

输出

True True False False

我知道为什么它在第一次比较时给出了真实和真实。因为它调用父类的重载==（）运算符。我的问题是我想使用子类的==运算符，因为对象是Child类型，所以它怎么可能呢？对于静态方法，不能使用虚拟关键字。

谢谢，

Answer 1

在编译时选择运算符的实现。运算符不是虚方法 - 子类的==运算符不会覆盖父类==运算符。

因此，让编译器选择子==运算符的唯一方法是让变量本身为Child类型，例如

 Child p = new Child() { _First = "Mitul", _Last = "Patel", Address="abc1"};
 Child p1 = new Child() { _First = "Mitul", _Last = "Patel", Address = "abc" };

或让==运算符调用Equals方法，并使Equals的Child实现覆盖父实现：

在Parent.cs中

：

// No need for these to be public- they should only be called internally.
protected virtual bool Equals(Parent that)
{
    if (ReferenceEquals(that, null))
        return false;
    else if (ReferenceEquals(that, this))
        return true;
    else
        return this._First.Equals(that._First) & this._Last.Equals(that._Last);
}

在Child.cs中：

// Notice I changed your argument type here...
protected override bool Equals(Parent that)
{
    // If we are not dealing with a Child instance, delegate to the base class.
    if (!(that is typeof(Child)))
        return base.Equals(that);

    if (ReferenceEquals(that, null))
        return false;
    else if (ReferenceEquals(that, this))
        return true;
    else
        return this.Address.Equals(that.Address) & base.Equals(that);
}

Answer 2

static方法在编译时解决，而不是在运行时解决对于您的代码p和p1是Parent个对象，因此它会调用==类的Parent运算符。
如果希望调用派生类的运算符，则必须将它们声明为派生类实例。

运算符重载和继承c＃

2 个答案: