GetEnumerator用法

GetEnumerator是返回实例的枚举数。换句话说就是返回集的中所有元素一个一个列出来。我们可以通过MoveNext()得到集合中的所有元素。

这里的名词稍微说明一下，

    枚举就：是一个一个的列举。

    枚举数：是循环访问其关联集合的对象。它提供一种方法帮助你遍历一个集合。

  

GetEnumerator用法请看下边代码中红色部分。 这里顺便作了测试。发现GetEnumerator要比Foreach稍微快一点。

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

using System.Diagnostics;
using System.Collections;

namespace GetEnumeratorTest
{
    class Program
    {
        static void Main(string[] args)
        {
            const int times =1000;
            Stopwatch watch = new Stopwatch();
            Hashtable hastable = new Hashtable();
            for (int i = 0; i < 10000; i++)
            {
                hastable.Add(i, i.ToString() + "值");
            }
            //测试GetEnumerator
            watch.Start();
            for (int i = 0; i < times; i++)
            {
                IDictionaryEnumerator enumerator = hastable.GetEnumerator();
                while (enumerator.MoveNext())
                {
                    string key = enumerator.Key.ToString();
                    string value = enumerator.Value.ToString();
                }
            }
            watch.Stop();
            Console.WriteLine("Hashtable GetEnumerator耗时" + watch.ElapsedMilliseconds);
            Console.WriteLine("---------------");

            watch.Reset();
            //测试ForEach
            watch.Start();
            for (int i = 0; i < times; i++)
            {
                foreach (object item in hastable.Keys)
                {
                    string key = item.ToString();
                    string value = hastable[item].ToString();
                }
            }
            watch.Stop();
            Console.WriteLine("Hashtable ForEach耗时" + watch.ElapsedMilliseconds);
            Console.WriteLine("---------------");

            watch.Reset();
            Dictionary<int, string> dictionary = new Dictionary<int, string>();
            for (int i = 0; i < 10000; i++)
            {
                dictionary.Add(i, i.ToString() + "值");
            }
            watch.Start();
            for (int i = 0; i < times; i++)
            {                
                Dictionary<int,string>.Enumerator enumerator = dictionary.GetEnumerator();
                while (enumerator.MoveNext())
                {
                    int key = enumerator.Current.Key;
                    string value = enumerator.Current.Value;
                }
            }
            watch.Stop();
            Console.WriteLine("Dictionary GetEnumerator耗时" + watch.ElapsedMilliseconds);
            Console.WriteLine("---------------");

            watch.Reset();
            //测试ForEach
            watch.Start();
            for (int i = 0; i < times; i++)
            {
                foreach (int item in dictionary.Keys)
                {
                    int key = item;
                    string value = dictionary[item];
                }
            }
            watch.Stop();
            Console.WriteLine("Dictionary ForEach耗时" + watch.ElapsedMilliseconds);
            Console.WriteLine("---------------");
            Console.ReadKey();
        }
    }
}

 结果：

    Hashtable GetEnumerator耗时 1584
    Hashtable ForEach耗时 1884
    Dictionary GetEnumerator耗时 365
    Dictionary ForEach耗时 375