当我使用词典时,有时我必须更改默认的等同含义才能比较键.我看到,如果我重写关键字类上的Equals和GetHashCode,或者我创建一个实现IEqualityComparer的新类,我有相同的结果.那么使用IEqualityComparer和Equals / GethashCode Override有什么区别？
两个例子：
两个例子：
class Customer
{
public string name;
public int age;
public Customer(string n,int a)
{
this.age = a;
this.name = n;
}
public override bool Equals(object obj)
{
Customer c = (Customer)obj;
return this.name == c.name && this.age == c.age;
}
public override int GetHashCode()
{
return (this.name + ";" + this.age).GetHashCode();
}
}
class Program
{
static void Main(string[] args)
{
Customer c1 = new Customer("MArk",21);
Customer c2 = new Customer("MArk",21);
Dictionary<Customer,string> d = new Dictionary<Customer,string>();
Console.WriteLine(c1.Equals(c2));
try
{
d.Add(c1,"Joe");
d.Add(c2,"hil");
foreach (KeyValuePair<Customer,string> k in d)
{
Console.WriteLine(k.Key.name + " ; " + k.Value);
}
}
catch (ArgumentException)
{
Console.WriteLine("Chiave già inserita in precedenza");
}
finally
{
Console.ReadLine();
}
}
}
}
第二个 ：
class Customer
{
public string name;
public int age;
public Customer(string n,int a)
{
this.age = a;
this.name = n;
}
}
class DicEqualityComparer : EqualityComparer<Customer>
{
public override bool Equals(Customer x,Customer y) // equals dell'equalitycomparer
{
return x.name == y.name && x.age == y.age;
}
public override int GetHashCode(Customer obj)
{
return (obj.name + ";" + obj.age).GetHashCode();
}
}
class Program
{
static void Main(string[] args)
{
Customer c1 = new Customer("MArk",21);
DicEqualityComparer dic = new DicEqualityComparer();
Dictionary<Customer,string>(dic);
Console.WriteLine(c1.Equals(c2));
try
{
d.Add(c1,string> k in d)
{
Console.WriteLine(k.Key.name + " ; " + k.Value);
}
}
catch (ArgumentException)
{
Console.WriteLine("Chiave già inserita in precedenza");
}
finally
{
Console.ReadLine();
}
}
}
}
两个例子都有相同的结果.
提前致谢.
解决方法
当您重写Equals和GetHashCode时,您正在改变对象将如何确定它是否等于另一个.和一个注释,如果使用==运算符比较对象,它将不会与Equals具有相同的行为,除非你也覆盖运算符.
这样做你改变了一个类的行为,如果你需要与其他类相同的逻辑怎么办？如果您需要“通用比较”.这就是为什么你有IEqualityComparer.
看这个例子(full code on Github)
interface ICustom
{
int Key { get; set; }
}
class Custom : ICustom
{
public int Key { get; set; }
public int Value { get; set; }
}
class Another : ICustom
{
public int Key { get; set; }
}
class DicEqualityComparer : IEqualityComparer<ICustom>
{
public bool Equals(ICustom x,ICustom y)
{
return x.Key == y.Key;
}
public int GetHashCode(ICustom obj)
{
return obj.Key;
}
}
我有两个不同的类,都可以使用相同的比较器.
var a = new Custom { Key = 1,Value = 2 };
var b = new Custom { Key = 1,Value = 2 };
var c = new Custom { Key = 2,Value = 2 };
var another = new Another { Key = 2 };
var d = new Dictionary<ICustom,string>(new DicEqualityComparer());
d.Add(a,"X");
// d.Add(b,"X"); // same key exception
d.Add(c,"X");
// d.Add(another,"X"); // same key exception
请注意,我没有必要在两个类中都覆盖Equals,GetHashCode.我可以在实现ICustom的任何对象中使用此比较器,而无需重写比较逻辑.我也可以为“父类”创建IEqualityComparer,并在继承的类上使用.我可以让比较者以不同的方式表现,我可以让一个比较Value而不是Key.
所以IEqualityComparer允许更多的灵活性,你可以实现通用的解决方案.
