最全数据结构详述: List VS IEnumerable VS IQueryable VS ICollection VS IDictionary

本文对常用的数据结构详述：Array, ArrayList，List，IList，ICollection, Stack, Queue, HashTable, Dictionary, IQueryable, IEnumerable。

Collection（集合）

Collection是数据记录集合，

编写代码过程中，常常需要合适的容器保存临时数据，方便修改和查找，如何选取合适的数据容器，关键在于将执行的数据操作以及数据记录是否大量。

Array（数组）

特征

1. 固定大小，数组的大小是初始化时决定无法修改的数值。

2. 强类型，存储数据元素类型必须在初始化时指定，因此在运行时，不需要耗费额外的时间来定义数组类型，能够大大提升运行效率。

3. 可使用Foreach关键字实现数组迭代和查找。

因为数组大小是固定的，且是强类型数据结构，因此在运行时只占用很少的内存，运行时效率很高。

//It is obvious that strArray is
      //1. string   --> Strongly Type
      //2. Sized=10 --> Fixed Size

      string[] strArray = new string[10];

      for (int i = 0; i < 10; i++)
      {
          if (strArray[i]==null)
          {
              strArray[i] = (i+1).ToString();
          }
      }

      this.ListBoxArray.DataSource = null;
      this.ListBoxArray.Items.Clear();

      this.ListBoxArray.DataSource = strArray;
      this.ListBoxArray.DataBind();

ArrayList

1. ArrayList 没有固定的长度，容量可动态增加，可应用于开发人员无法确定数组元素个数等场景，当然这种情况下，在定义结构体的时候会非常耗时。

2. ArrayList 不是强类型，ArrayList中不同元素类型可以不相同，并且需要在运行时根据实际的输入来确定元素类型。因此在运行时消耗内存较多。

3. 可使用Froeach 关键字操作ArrayList。

public class Product
    {
        public Product()
        {

        }
        public Product(string Code, string Name)
        {
            _Code = Code;
            _Name = Name;
        }

            public string _Code {get; set;}
            public string _Name { get; set; }
    }

ArrayList支持String,int,以及十进制小数类型。

//It is NOT obvious that strArrayList is 1. string? int? object? decimal?  --> NOT Strongly Type
 //                                       2. Sized=10? 20? 100?             -->NOT Fixed Size
 // Namespace: System.Collections

 System.Collections.ArrayList strArrayList = new System.Collections.ArrayList();
 //System.Linq.IQueryable  type of data is not specific runtime defered support
 strArrayList.Add("Mahsa");  //   "Mahsa": is string
 strArrayList.Add(1);        //        1 : is integer
 strArrayList.Add(0.89);     //      0.89: is decimal

 this.ListBoxArrayList.DataSource = null;
 this.ListBoxArrayList.Items.Clear();
 this.ListBoxArrayList.DataSource = strArrayList;
 this.ListBoxArrayList.DataBind();

 System.Text.StringBuilder str= new System.Text.StringBuilder();

 foreach (var item in strArrayList)
 {
     str.Append(" , "+item);
 }
 this.lblArrayList.Text = str.ToString();

 //Below is old way to fill obj from product , in Arraylist you need to create more than one instance
// Product objProduct = new Product();
// objProduct.Code = "1001";
// objProduct.Name = "Chair";

 //It is NOT obvious that strArrayList is
 //1. string? int? object? decimal? OR OBJECT??  --> NOT Strongly Type
 //2. Sized=10? 20? 100?                         -->NOT Fixed Size
 // Namespace: System.Collections

 System.Collections.ArrayList objArrayList = new System.Collections.ArrayList();

 objArrayList.Add(new Product("1001", "Chair"));
 objArrayList.Add(new Product("1002", "Sofa"));
 objArrayList.Add(new Product("1003", "Carpet"));

 this.DropDownListArrayListObject.DataSource = null;
 this.DropDownListArrayListObject.Items.Clear();
 this.DropDownListArrayListObject.DataSource = objArrayList;

 //* Finding among Object of Array List is difficult , you have to find your specific item by index
 Product objTemp = (Product)objArrayList[0];
 objArrayList.Remove(objTemp);
 //*
 this.DropDownListArrayListObject.DataTextField = "_Name";
 this.DropDownListArrayListObject.DataValueField = "_Code";
 this.DropDownListArrayListObject.DataBind();
 this.GridViewArrayListObject.DataSource = objArrayList;
 this.GridViewArrayListObject.DataBind();

HashTable（哈希表）

HashTable是一种定义关键字的数据结构体，使用哈希表查找数据非常方便，哈希表既不是强类型也不固定大小限制。

//It is NOT obvious that strArrayList is
       //1. string? int? object? decimal? OR OBJECT??  --> NOT Strongly Type
       //2. Sized=10? 20? 100?                         -->NOT Fixed Size
       // Namespace: System.Collections
       //Hashtable solve the problem in Arraylist when we are looking for specific item
       //Hashtable dedicate a key for each item, then finding item is easier and faster

        System.Collections.Hashtable objHashTable = new System.Collections.Hashtable();

        objHashTable.Add("1001","Chair");
        objHashTable.Add("1002", "Sofa");
        objHashTable.Add("1003", "Carpet");


       this.DropDownListHashTable.DataSource = null;
       this.DropDownListHashTable.Items.Clear();
       this.DropDownListHashTable.DataSource = objHashTable;
       //* finding item is easier you just need to point to it by call its key
       objHashTable.Remove("1002");
       //*
       this.DropDownListHashTable.DataTextField = "Value";
       this.DropDownListHashTable.DataValueField = "Key";
       this.DropDownListHashTable.DataBind();

Stack

栈是最典型的数据结构，栈具有优先级划分的数据结构，栈为每个内容项定义优先级，表示每个Item入栈和出栈的优先顺序。因此操作栈中的数据，需要先将数据push 到栈的顶部，需要删除元素必须变成栈顶部，即要遵守后进先出（LIFO）的原则。

栈与哈希表一样既不是强类型也不限制元素个数。

Push 操作

//Stack is LIFO: Last in First Out
       System.Collections.Stack objStackPush = new System.Collections.Stack();

       //By Push method you can insert item at the top of the stack
       objStackPush.Push("Mahsa");
       objStackPush.Push("Hassankashi");
       this.lblPop.Text = "";
       this.ListBoxStack.DataSource = objStackPush.ToArray();
       this.ListBoxStack.DataBind();

Pop操作

System.Collections.Stack objStackPop = new System.Collections.Stack();

objStackPop.Push("Mahsa");
objStackPop.Push("Hassankashi");

//By Pop method you can remove item from the top of the stack --> Last in First in
this.lblPop.Text = objStackPop.Pop().ToString();

this.ListBoxStack.DataSource = objStackPop.ToArray();
this.ListBoxStack.DataBind();

Queue

Queue同栈一样也是具有优先级定义的结构体，遵循的规则是先进先出（FIFO），既不是强类型也不具有固定的大小限制。

入队操作

   1:  //Queue is FIFO: First in First Out

   2:  System.Collections.Queue objQueue = new System.Collections.Queue();

   3:   

   4:  //By Enqueue method you can insert item at the END of the Queue

   5:  objQueue.Enqueue("Mahsa");

   6:  objQueue.Enqueue("Hassankashi");

   7:  objQueue.Enqueue("Cosmic");

   8:  objQueue.Enqueue("Verse");

   9:   

  10:  this.lblQueue.Text = "";

  11:  this.ListBoxQueue.DataSource = objQueue.ToArray();

  12:  this.ListBoxQueue.DataBind();

出队操作

System.Collections.Queue objQueue = new System.Collections.Queue();

objQueue.Enqueue("Mahsa");
objQueue.Enqueue("Hassankashi");
objQueue.Enqueue("Cosmic");
objQueue.Enqueue("Verse");

//By Dequeue method you can remove item from the BEGINING of the Queue --> First in First out FIFO
this.lblQueue.Text=objQueue.Dequeue().ToString();

this.ListBoxQueue.DataSource = objQueue.ToArray();
this.ListBoxQueue.DataBind();

入队操作

System.Collections.Queue objQueue = new System.Collections.Queue();

objQueue.Enqueue("Mahsa");
objQueue.Enqueue("Hassankashi");
objQueue.Enqueue("Cosmic");
objQueue.Enqueue("Verse");

//By Dequeue method you can remove item from the BEGINING of the Queue --> First in First out FIFO
this.lblQueue.Text=objQueue.Dequeue().ToString();

this.ListBoxQueue.DataSource = objQueue.ToArray();
this.ListBoxQueue.DataBind();

List

什么情况下需要使用List？

1. List长度可不固定

2. 当数据为通用类型，List是强类型，List中元素类型不需要等到运行时来确定，这种特性使得List 运行时效率非常高。

3. 可使用Foreach关键字。

因为List不需要设定固定的大小，List灵活度高，且效率高常用于开发过程中。

//Like Array is Strong Type
//Like ArrayList with No Dimension
System.Collections.Generic.List<string> strList = new List<string>();


strList.Add("Mahsa");
strList.Add("Hassankashi");
strList.Add("Cosmic");
strList.Add("Verse");

this.ListBoxListGeneric.DataSource = strList;
this.ListBoxListGeneric.DataBind();

System.Text.StringBuilder str = new System.Text.StringBuilder();

foreach (var item in strList)
{
    str.Append(" , " + item);
}
this.lblList.Text = str.ToString();

IList

IList 继承了List，包含多种方法的List接口。如果你无法判断代码改动的可能性，可以使用IList接口，减少模块之间的依赖性。IList是接口因此无法被实例化，所以必须使用List来初始化。

System.Collections.Generic.IList<string> strIList = new List<string>();

我们一起了解一下具体的类和接口之间的区别。

1. 具体类可继承其他类，并实现一个或多个接口。

2. 在内部类中可以定义变量并赋值，接口中不允许此操作。

3. 具体类可包含构造函数，而接口中不能定义构造函数

4. 抽象类中可包含访问修饰符如public,private等，接口中不能包含。

//Ilist can not be instantiate from Ilist , so it should be instantiate from List
System.Collections.Generic.IList<string> strIList = new List<string>();

strIList.Add("Mahsa");
strIList.Add("Hassankashi");
strIList.Add("Cosmic");
strIList.Add("Verse");


this.ListBoxListGeneric.DataSource = strIList;
this.ListBoxListGeneric.DataBind();

System.Text.StringBuilder str = new System.Text.StringBuilder();

foreach (var item in strIList)
{
    str.Append(" , " + item);
}
this.lblList.Text = str.ToString();

IEnumerable

IEnumerable常用于遍历集合元素，但是无法修改（删除或添加）数据，使用IEnumberable 会从服务器端将所有数据拷贝到客户端，并进行一定的过滤，如果服务器端有大量数据会造成内存负载超重。

//IEnumerable can not be instantiate from Enumerable , so it should be instantiate from List
       System.Collections.Generic.IEnumerable<Employee> empIEnumerable = new List<Employee>
       {   new Employee { ID = 1001, Name="Mahsa"},
           new Employee { ID = 1002, Name = "Hassankashi" },
           new Employee { ID = 1003, Name = "CosmicVerse" },
           new Employee { ID = 1004, Name = "Technical" }
       };


       this.GridViewIEnumerable.DataSource = empIEnumerable;
       this.GridViewIEnumerable.DataBind();

       System.Text.StringBuilder str = new System.Text.StringBuilder();

       foreach (Employee item in empIEnumerable)
       {
           str.Append(" , " + item.ID +"-"+item.Name);
       }

       this.lblIEnumerable.Text = str.ToString();

IQueryable

IQueryable与IEnumberable不同的是，当从服务器端加载过量的数据，IQueryable会自动减少应用负载。IQueryable可保证大数据量时应用程序的高性能。

IQueryable会先过滤数据，然后发送给客户端。

DataAccessEntities ctx = new DataAccessEntities();
        var ctx = new DataAccessEntities();

//Difference between IQueryable and IEnumerable

        //You can instantiate IEnumerable from List

        IEnumerable<employee> queryIEnumerable = new List<employee>() ;


        //Bring  ALL records from server --> to client then filter collection
       //To bring all data from server you should omit where cluse from linq to sql
        queryIEnumerable = from m in ctx.Employees select m;

        //If you use where as extension method with IEnumerable then All records will be loaded
        queryIEnumerable = queryIEnumerable.Where(x => x.ID == 1).ToList();



        //You can not instantiate IQueryable

        IQueryable<employee> queryIQueryable=null;

        //Bring just ONE record from server --> to client

        queryIQueryable = (from m in ctx.Employees
                     where m.ID == 1
                     select m);

        //Whenever you call IQueryable so ==> It will be executed
        this.GridViewIQueryable.DataSource = queryIQueryable.ToList();
        this.GridViewIQueryable.DataBind();
</employee>

SQL Profiler:

如何追踪查询语句生成TSQL，生成需要的数据结构体：

Step 1:

Start -> MS SQL Server 2008 -> Performance Tools -> SQL Server Profiler

Step 2:

SQL Server Profiler -> File -> New Trace

Step 3:

输入连接数据库的用户名和密码

Step 4:

General (Tab) -> Use the Template: Standard

Step 5:

Event Selection (Tab) -> Event : TSQL -> Select : SQL-BatchCompleted | Select Show all Columns

Press Column Filter -> Database Name: Like: "DataAccess"

运行

Step 6:

查看结果

Step 7:

生成 IEnumerable数据 :

SELECT
[Extent1].[ID] AS [ID],
[Extent1].[Name] AS [Name],
[Extent1].[Age] AS [Age]
FROM [dbo].[Employee] AS [Extent1]

生成 IQueryable :

SELECT 
[Extent1].[ID] AS [ID], 
[Extent1].[Name] AS [Name], 
[Extent1].[Age] AS [Age]
FROM [dbo].[Employee] AS [Extent1]
WHERE 1 = [Extent1].[ID]

ICollection 继承了IEnumberable，但是IEnumberable是基于索引的，ICollection不基于索引。

//IList {indexer and Modify} vs ICollection {randomly and Modify}
 //Collection can not be instantiate from ICollection , so it should be instantiate from List
 System.Collections.Generic.ICollection<string> strICollection = new List<string>();
 strICollection.Add("Mahsa");
 strICollection.Add("Hassankashi");

 //Countable***
 int ICollectionCount=strICollection.Count;

 this.ListBoxICollection.DataSource = strICollection;
 this.ListBoxICollection.DataBind();
 System.Text.StringBuilder str = new System.Text.StringBuilder();
 foreach (var item in strICollection)
 {
     str.Append(" , " + item);
 }
 this.lblICollection.Text = str.ToString();

 //IList***
 System.Collections.Generic.IList<Employee> objIList = new List<Employee>();
 objIList = (from m in ctx.Employees
             select m).ToList();

Employee obj = objIList.Where(i => i.Name == "Sara").FirstOrDefault();
int indexofSara= objIList.IndexOf(obj);
int cIList = objIList.Count;

 //ICollection***
 System.Collections.Generic.ICollection<Employee> objICollection = new List<Employee>();
 objICollection = (from m in ctx.Employees
                   select m).ToList();
 Employee objIC = objICollection.Where(i => i.Name == "Sara").FirstOrDefault();
 //You can not get index of object , if you clear comment from below code appears error
// int indexofSaraICollection = objIC.IndexOf(objIC);
 int cICollection = objICollection.Count;

Stack Generic

入栈：

//Stack is LIFO: Last in First Out
       //Here is for Push Stack in Generic
       //System.Collections.Stack objStackPush = new System.Collections.Stack();
       //Stack<T> can be instantiated from Stack<T>

       System.Collections.Generic.Stack<int> objStackPush = new System.Collections.Generic.Stack<int>();

       objStackPush.Push(1);
       objStackPush.Push(2);

       this.lblPopGeneric.Text = "";
       this.ListBoxStackGeneric.DataSource = objStackPush.ToArray();
       this.ListBoxStackGeneric.DataBind();

出栈：

//Stack is LIFO: Last in First Out
       //Here is for Pop Stack in Generic
       //System.Collections.Stack objStackPop = new System.Collections.Stack();
       //Stack<T> can be instantiated from Stack<T>

       System.Collections.Generic.Stack<int> objStackPop = new System.Collections.Generic.Stack<int>();

       objStackPop.Push(1);
       objStackPop.Push(2);

       this.lblPop.Text = objStackPop.Pop().ToString();
       this.ListBoxStack.DataSource = objStackPop.ToArray();
       this.ListBoxStack.DataBind();

Queue Generic

入队：

//Queue is FIFO: First in First Out
       //Here is for Enqueue Queue in Generic
       //System.Collections.Queue objQueue = new System.Collections.Queue();
       //Queue<T> can be instantiated from Queue<T>

       System.Collections.Generic.Queue<int> objQueue = new System.Collections.Generic.Queue<int>();
       objQueue.Enqueue(1);
       objQueue.Enqueue(2);

       this.lblQueue.Text = "";

       this.ListBoxQueue.DataSource = objQueue.ToArray();
       this.ListBoxQueue.DataBind();

出队：

//Queue is FIFO: First in First Out
       //Here is for Enqueue Queue in Generic
       //System.Collections.Queue objQueue = new System.Collections.Queue();
       //Queue<T> can be instantiated from Queue<T>

       System.Collections.Generic.Queue<int> objQueue = new System.Collections.Generic.Queue<int>();
       objQueue.Enqueue(1);
       objQueue.Enqueue(2);

       this.lblQueue.Text = "";

       this.ListBoxQueue.DataSource = objQueue.ToArray();
       this.ListBoxQueue.DataBind();

Dictionary 及 IDictionary：

Dictionary 可通用，而哈希表不是通用的。Dictionary定义 <TKey，Tvalue>。IDictionary是Dictionary的接口，如果在后期开发中需要大量修改，建议使用IDictionary。

//Dictionary can instantiate from Dictionary , Dictionary is similar to Hashtable,
//Dictionary is GENERIC but Hashtable is NON GENERIC
//Such Hashtable you can find object by its key
System.Collections.Generic.Dictionary<int, string=""> objDictionary = new Dictionary<int, string="">();

objDictionary.Add(1001, "Mahsa");
objDictionary.Add(1002, "Hassankashi");
objDictionary.Add(1003, "Cosmicverse");

string str = objDictionary[1002];

this.ListBoxDictionary.DataSource = objDictionary;
this.ListBoxDictionary.DataBind();</int,>