比较用作词典中的键的对象 [英] Comparing object used as Key in Dictionary

问题描述

我的课程：

  public class myClass 
 {
 public int A {get;组; } 
 public int B {get;组; } 
 public int C {get;组; } 
 public int D {get;组; 
} 
  

主要示例：

 字典< myClass，List< string>> dict = new Dictionary< myClass，List< string>>（）; 
 myClass first = new myClass（）; 
 first.A = 2; 
 first.B = 3; 
 
 myClass second = new myClass（）; 
 second.A = 2; 
 second.B = 3; 
 second.C = 5; 
 second.D = 6; 
 
 dict.Add（first，new List< string>（））; 
 
 if（dict.ContainsKey（second））
 {
 // 
 //应该来这里并更新列表< string>对于第一个（仅在本例中）键
 // 
} 
 else 
 {
 // 
 //如果myFirst对象有不同的vlues A或B属性
 // 
 dict.Add（第二，新的List< string>（））; 
} 
  

如何做？

解决方案

如果您总是希望字典仅在A和B上进行比较，则有两种选择。 使用实现 IEqualityComparer< TKey> 并将您的比较逻辑放在那里，或让您的课程实施 IEquateable< T> GetHashCode和Equals ，所以默认比较器会给你所需的结果。 / p>

如果您只想在A和B中进行比较，您将需要使用.Keys比例和Linq扩展方法包含，允许您传入一个 IEqualityComparer< T>

  public class MyClassSpecialComparer：IEqualityComparer< myClass> 
 {
 public bool Equals（myClass x，myClass y）
 {
 return x.A == y.A&& x.B == y.B 
} 
 
 public int GetHashCode（myClass x）
 {
 return x.A.GetHashCode（）+ x.B.GetHashCode（）; 
} 
 
 
} 
 
 
 //特殊情况下，当您只想比较一次
 / /注意：这将比正常查找慢得多。 
 var myClassSpecialComparer = new MyClassSpecialComparer（）; 
字典< myClass，List< string>> dict = new Dictionary< myClass，List< string>>（）; 
 //（Snip）
 if（dict.Keys.Contains（second，myClassSpecialComparer））
 {
 // 
 //应该来这里并更新列表<串GT;对于第一个（仅在本例中）键
 // 
} 
 
 //如果您希望它始终比较
 Dictionary< myClass，List< string> > dict = new Dictionary< myClass，List< string>>（new MyClassSpecialComparer（））; 
  

my class:

public class myClass
{
    public int A { get; set; }
    public int B { get; set; }
    public int C { get; set; }
    public int D { get; set; }
}

and main example:

Dictionary<myClass, List<string>> dict = new Dictionary<myClass, List<string>>();
myClass first = new myClass();
first.A = 2;
first.B = 3;

myClass second = new myClass();
second.A = 2;
second.B = 3;
second.C = 5;
second.D = 6;

dict.Add(first, new List<string>());

if (dict.ContainsKey(second))
{
    //
    //should come here and update List<string> for first (and only in this example) key 
    //
}
else
{
    //
    //if myFirst object has difference vlues of A or B properties
    //
    dict.Add(second, new List<string>());
}

How to do this?

解决方案

If you always want the dictionary only to compare on A and B, you have two options. Either use the constructor that implements IEqualityComparer<TKey> and put your comparison logic there, or have your class implement IEquateable<T> GetHashCode and Equals so the default comparer will give you the results you are looking for.

If you only want to compare on A and B in your one situation you will need to use the .Keys proporty and the Linq extension method Contains that allows you to pass in a IEqualityComparer<T>

public class MyClassSpecialComparer : IEqualityComparer<myClass>
{
    public bool Equals (myClass x, myClass y)
    { 
        return x.A == y.A && x.B == y.B 
    }

    public int GetHashCode(myClass x)
    {
       return x.A.GetHashCode() + x.B.GetHashCode();
    }


}


 //Special case for when you only want it to compare this one time
 //NOTE: This will be much slower than a normal lookup.
    var myClassSpecialComparer = new MyClassSpecialComparer();
    Dictionary<myClass, List<string>> dict = new Dictionary<myClass, List<string>>();
    //(Snip)
    if (dict.Keys.Contains(second, myClassSpecialComparer ))
    {
        //
        //should come here and update List<string> for first (and only in this example) key 
        //
    }

 //If you want it to always compare
    Dictionary<myClass, List<string>> dict = new Dictionary<myClass, List<string>>(new MyClassSpecialComparer());

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