将对象的字段用作通用字典键 [英] Using the field of an object as a generic Dictionary key

问题描述

如果我想使用对象作为 Dictionary 的关键字，我需要重写哪些方法才能以特定方式进行比较？

假设我有一个有属性的类：

$ p $ class Foo {
公共字符串名称{get;组; }
public int FooID {get;组; }

//已删除
}


我想创建一个：

  Dictionary< Foo，List< Stuff>> 
  

我想要 Foo code> FooID 被视为同一组。我需要在 Foo 类中重写哪些方法？

总结：我想将 Stuff 对象放入列表中，按 Foo 对象进行分组。 Stuff 对象将有一个 FooID 来将它们链接到它们的类别。

GetHashCode（）和 Equals（）解决方案

code>。如果两个事物相等（ Equals（）返回true），它们具有相同的散列码是非常重要的。例如，你可能会返回FooID;作为 GetHashCode（），如果你想要这个匹配。您也可以实现 IEquatable< Foo> ，但这是可选的：



  class Foo：IEquatable< Foo> {
 public string Name {get; set;} 
 public int FooID {get; set;} 
 
 public override int GetHashCode（）{
 return FooID; 
} 
 public override bool Equals（object obj）{
 return Equals（obj as Foo）; 
} 
 public bool Equals（Foo obj）{
 return obj！= null&& obj.FooID == this.FooID; 
 
 
 
 
 
 
 $ b最后，另一种方法是提供一个 IEqualityComparer< T> 做同样的事情。
 
If I want to use objects as the keys for a Dictionary, what methods will I need to override to make them compare in a specific way?

Say I have a a class which has properties:
class Foo {
    public string Name { get; set; }
    public int FooID { get; set; }

    // elided
} 
And I want to create a:
Dictionary<Foo, List<Stuff>>
I want Foo objects with the same FooID to be considered the same group.  Which methods will I need to override in the Foo class?

To summarize: I want to categorize Stuff objects into lists, grouped by Foo objects. Stuff objects will have a FooID to link them to their category.
解决方案
By default, the two important methods are GetHashCode() and Equals(). It is important that if two things are equal (Equals() returns true), that they have the same hash-code. For example, you might "return FooID;" as the GetHashCode() if you want that as the match. You can also implement IEquatable<Foo>, but that is optional:
class Foo : IEquatable<Foo> {
    public string Name { get; set;}
    public int FooID {get; set;}

    public override int GetHashCode() {
        return FooID;
    }
    public override bool Equals(object obj) {
        return Equals(obj as Foo);
    }
    public bool Equals(Foo obj) {
        return obj != null && obj.FooID == this.FooID;
    }
}
Finally, another alternative is to provide an IEqualityComparer<T> to do the same.

                        
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