我特别关注引用类型中的内容相等性.在任何一种情况下,我都不会压倒平等 – 所以为什么行为会有所不同.
参见2个简单的代码示例：
示例1：返回True
class Program
{
static void Main(string[] args)
{
object o1 = "ABC";
object o2 = "ABC";
Console.WriteLine("object1 and object2: {0}",o1.Equals(o2));
}
}
示例2：两个语句都返回False
class Program
{
static void Main(string[] args)
{
Person person1 = new Person("John");
Person person2 = new Person("John");
Console.WriteLine("person1 and person2: {0}",person1.Equals(person2));
Console.WriteLine("person1 and person2: {0}",((object)person1).Equals((object)person2));
Console.ReadLine();
}
}
public class Person
{
private string personName;
public Person(string name)
{
this.personName = name;
}
}
解决方法
这里有两种效果：
>字符串实习意味着即使您执行引用相等性检查,您仍然会看到True.你可以像这样修复：
object o1 = new StringBuilder("ABC").ToString();
object o2 = new StringBuilder("ABC").ToString();
> System.String overrides the Equals method比较字符串的内容：
This method performs an ordinal (case-sensitive and culture-insensitive) comparison.
你可以在这里看到不同之处：
object o1 = new StringBuilder("ABC").ToString();
object o2 = new StringBuilder("ABC").ToString();
Console.WriteLine(o1.Equals(o2)); // Prints True due to overriding
Console.WriteLine(ReferenceEquals(o1,o2)); // Prints False
你的类不会覆盖Equals,所以你得到default implementation in Object,这是比较引用：
If the current instance is a reference type,the Equals(Object) method tests for reference equality,and a call to the Equals(Object) method is equivalent to a call to the ReferenceEquals method.
你可以通过重写Equals来合理地解决这个问题：
// It's easier to implement equality correctly on sealed classes
public sealed class Person
{
private readonly string personName;
public Person(string name)
{
if (name == null)
{
throw new ArgumentNullException("name");
}
this.personName = name;
}
public override bool Equals(object other)
{
Person person = other as Person;
return person != null && person.personName.Equals(personName);
}
// Must override GetHashCode at the same time...
public override int GetHashCode()
{
// Just delegate to the name here - it's the only thing we're
// using in the equality check
return personName.GetHashCode();
}
}
请注意,在Equals实现中,我们可以使用：
return person != null && person.personName == personName;
…因为string也会重载==运算符.但那是另一回事:)
