如何在C＃中为每个类实例分配一个整数ID？ [英] How to assign an integer ID to each class instace in C#?

问题描述

假设我有几个班级的实例



公共班级AB

{

}



在main我创建AB类实例



AB a = new AB（）;

AB b = new AB（）;

AB c = new AB（）;

......





i想要将每个类实例映射到一个整数ID。我怎么能在c＃中做到这一点？



我尝试了什么：



我试过枚举。和字典。字典的问题是，如果我改变实例的顺序，那么即使ID也会改变。如果ID为0，我需要类似

的东西，如果ID为1，则需要使用

，如果ID为2则使用b

，c应该使用等等



但是我不想使用if / else和switch

解决方案

< blockquote>你可以使用一个数组：

  private  AB [] AllInstances =  new  AB [ 3 ]; 
 ... 
 AB a =  new  AB（）; 
 AllInstances [ 0 ] = a; 
 AB b =  new  AB（）; 
 AllInstances [ 1 ] = b; 
 AB c =  new  AB（）; 
 AllInstances [ 2 ] = c; 

然后您只需按ID访问数组作为索引：

 AB it = AllInstances [ID]; 

或者，您可以将ID值作为属性添加到AB类，并且添加静态集合：

  private   static 列表< AB> AllInstances =  new 列表< AB> 

然后在AB构造函数中将其添加到集合中：

  public  AB（ int  id）
 {
 ID = ID; 
 AllInstances.Add（ this ）; 
} 

您只需要使用Linq来获取实例：

  public  AB Get（ int  id）
 {
  return  AllInstances.Where（ab = >  ab.ID == id）.FirstOrDefault（）; 
} 

字典的问题是，如果我改变实例的顺序，那么即使是ID更改。

该声明没有意义。虽然你应该永远不要依赖在一个字典中的KeyValuePairs中，然后将它们放入（或者，任何顺序），使用字典保证......事实上它不允许重复的密钥...每个密钥都是唯一的。



我认为（猜测）你想要的是每个密钥的唯一id（int）类的实例;你能做到的一种方法是：

 使用 System.Collections.Generic; 
 
 命名空间 YourNameSpace 
 {
  public   class  AB 
 {
  private   static   int  AB_ID =  0 ; 
 
  public   static 字典< AB，int> ABInstanceToID =  new 字典< AB，int>（）; 
 
  public   int  ID {设置;  get ; } 
 
  public  AB（）
 {
  this  .ID = AB_ID; 
 ABInstanceToID.Add（ this ， this  .ID）; 
 AB_ID ++; 
} 
} 
} 

因此，给定AB的运行时实例，您可以通过在静态字典中进行查找来读取其ID：

  if （AB.ABInstanceToID.ContainsKey（someAB））
 {
  int  index = AB.ABInstanceToID [someAB]; 
 
  switch （index）
 {
  case   0 ：
  //  句柄O  
  break ; 
 
 默认：
  break ; 
} 
} 
  else  
 {
  //  抛出错误？ 
  //  使用MessageBox发出警告 ？>  
}  

注意：



1.in理论'ContainsKey测试不应该是必要的，但我认为检查和重新检查以及计划错误总是一个好主意。 br />


2.虽然有些人可能更喜欢使用Dictionary.TryGetValue进行检查，在这种情况下，我们可以假设经常尝试查找丢失的密钥是非常不可能的，我认为没有理由在这里使用它。

试试这个

 AB a =  new  AB（）; 
 AB b =  new  AB（）; 
 AB c =  new  AB（）; 
 AB d =  new  AB（）; 
 AB e =  new  AB（）; 
 
 AB [] array =  new  AB [ 5 ]; 
 array [ 0 ] = a; 
 array [ 1 ] = b; 
 array [ 2 ] = c; 
 array [ 3 ] = d; 
 array [ 4 ] = e; 
 
  int  id =  2 ; 
  var  instance = array [id];  //  获取c的实例 
 

lets say i have few instances of the class

public class AB
{
}

in main i create instances of class AB

AB a = new AB();
AB b = new AB();
AB c = new AB();
......


i want to map each class instance to an integer ID. How can i do that in c#?

What I have tried:

I tried enums. and dictionary. The problem with dictionary is that if i change the order of the instances, then even the ID changes. I want something like
if ID is 0, a should be used
if ID is 1, b should be used
if ID is 2, c should be used and so on

but i dont want to use if/else and switch

解决方案

You could use an array:

private AB[] AllInstances = new AB[3];
...
    AB a = new AB();
    AllInstances[0] = a;
    AB b = new AB();
    AllInstances[1] = b;
    AB c = new AB();
    AllInstances[2] = c;

Then you just access the array by ID as an index:

AB it = AllInstances[ID];

Alternatively, you could add the ID value to your AB class as a property, and add a static collection:

private static List<AB> AllInstances = new List<AB>

Then in the AB constructor add it to the collection:

public AB(int id)
   {
   ID = id;
   AllInstances.Add(this);
   }

All you need then is to use Linq to get the instance:

public AB Get(int id)
   {
   return AllInstances.Where(ab => ab.ID == id).FirstOrDefault();
   }

"The problem with dictionary is that if i change the order of the instances, then even the ID changes."

That statement does not make sense. While it is correct that you should never rely on the KeyValuePairs in a Dictionary being in the same "order" you put them in (or, any order), using a Dictionary guarantees ... by virtue of the fact it does not allow duplicate Keys ... that each key is unique.

I think (guess) what you want is a unique id (int) for each instance of the Class; one way you can do that is:

using System.Collections.Generic;

namespace YourNameSpace
{
    public class AB
    {
        private static int AB_ID = 0;

        public static Dictionary<AB, int> ABInstanceToID = new Dictionary<AB, int>();

        public int ID { set; get; }

        public AB()
        {
            this.ID = AB_ID;
            ABInstanceToID.Add(this, this.ID);
            AB_ID++;
        }
    }
}

So, given a run-time instance of AB, you can read its ID by doing a lookup in the static Dictionary:

if(AB.ABInstanceToID.ContainsKey(someAB))
{
       int index = AB.ABInstanceToID[someAB];

       switch(index)
       {
           case 0:
              // handle case O
              break;

           default:
              break;
       }
}
else
{
     // throw an error ?
     // put up a warning with a MessageBox ?>
}

Note:

1.in "theory" the 'ContainsKey test should not be necessary, but I think it's always a good idea to check and re-check, and plan for errors.

2. while some might favor using Dictionary.TryGetValue for the check, in this case, where we can assume frequent attempts at look-up of missing Keys is very improbable, I see no reason to use that, here.

try this

AB a = new AB();
AB b = new AB();
AB c = new AB();
AB d = new AB();
AB e = new AB();

AB[] array = new AB[5];
array[0] = a;
array[1] = b;
array[2] = c;
array[3] = d;
array[4] = e;

int id = 2;
var instance = array[id];  // gets instance for c

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