如何检查对象是否等于同一类的新对象？

Question

如果我有一个像这样的对象:

public class Person
{
    public int id {get;set;}
    public string name {get;set;}
}

我想要的行为:

Person a = new Person();
Person b = new Person();

a == b;

并且a == b返回true,我是否必须覆盖Object.Equals()方法？或者是否有其他方法可以不覆盖Equals方法？

编辑

我想比较数据,因为我想知道我调用的外部方法是否返回一个新对象或一个具有不同于新对象的数据的对象

Answer 1

有几种方法可以做到这一点.默认情况下,Equals()并==检查是否有参考平等,意思是:

Person a = new Person();
Person b = a:

a.Equals(b); //true
a == b; //true

因此,不会将对象与值相等进行比较,这意味着:

Person a = new Person { id = 1, name = "person1" };
Person b = new Person { id = 1, name = "person1" };

a.Equals(b); //false
a == b; //false

要比较对象的值,可以覆盖Equals()和GetHashcode()方法,如下所示:

public override bool Equals(System.Object obj)
{
    if (obj == null)
        return false;

    Person p = obj as Person;
    if ((System.Object)p == null)
        return false;

    return (id == p.id) && (name == p.name);
}

public bool Equals(Person p)
{
    if ((object)p == null)
        return false;

    return (id == p.id) && (name == p.name);
}

public override int GetHashCode()
{
    return id.GetHashCode() ^ name.GetHashCode();
}

现在,您将在比较时看到其他结果:

Person a = new Person { id = 1, name = "person1" };
Person b = new Person { id = 1, name = "person1" };
Person c = a;

a == b; //false
a == c; //true
a.Equals(b); //true
a.Equals(c); //true

该==运营商不被覆盖,因此仍然没有参考比较.这可以通过重载它以及!=运算符来解决:

public static bool operator ==(Person a, Person b)
{
    if (System.Object.ReferenceEquals(a, b))
        return true;

    if ((object)a == null || (object)b == null)
        return false;

    return a.id == b.id && a.name == b.name;
}

public static bool operator !=(Person a, Person b)
{
    return !(a == b);
}

现在运行检查结果如下:

Person a = new Person { id = 1, name = "person1" };
Person b = new Person { id = 1, name = "person1" };
Person c = a;

a == b; //true
a == c; //true
a.Equals(b); //true
a.Equals(c); //true

更多阅读:

• 实施平等和平等操作员指南(==)