一直想写一系列如何提高Performance和Scalability的文章，把我的相关经验和所知道的相关的技巧同大家分享。前一阵在园子里有一篇讨论for each 和 for两种循环那个具有更好的performance的blog，议论得沸沸扬扬。我觉得这是一个很好的切入点，我就已此作为引子，开始我的这个系列的文章。这篇文章的重点不是在于比较这两种循环孰优孰劣，我将讨论的重点是如何更好地定义Collection，如何在判断在什么时候该用Array，什么时候用Collection。
一、for each的本质
我们知道，所有实现了System.Collections. IEnumerable接口的类，我们都可以对它运用for each loop。为了弄清楚它的执行过程，我先给出一个Sample：
using System;
using System.Collections.Generic;
using System.Text;
using System.Collections;
namespace Artech.CustomCollection
{
struct Employee
{
Private Fields#region Private Fields
private string _employeeID;
private string _name;
private int _age;
#endregion
Constructor#region Constructor
public Employee(string employeeID, string name, int age)
{
this._employeeID = employeeID;
this._name = name;
this._age = age;
}
#endregion
Public Properties#region Public Properties
public string EmployeeID
{
get { return _employeeID; }
set { _employeeID = value; }
}
public string Name
{
get { return _name; }
set { _name = value; }
}
public int Age
{
get { return _age; }
set { _age = value; }
}
#endregion
Tostring#region Tostring
public override string ToString()
{
return string.Format("\tID: \t{0}\n\tName: \t{1}\n\tAge:\t{2}\n\t", this._employeeID, this._name, this._age);
}
#endregion
}
class EmployeeList : IEnumerable
{
private Employee[] _employees;
public Employee[] Employees
{
get { return _employees; }
set { _employees = value; }
}
IEnumerable Members#region IEnumerable Members
public virtual IEnumerator GetEnumerator()
{
Console.WriteLine("EmployeeList.GetEnumerator() is invoked");
return new GenericEmployeeEnumerator(this._employees);
}
#endregion
}
class EmployeeEnumerator : IEnumerator
{
private Employee[] _employees;
private int _index = -1;
public EmployeeEnumerator(Employee[] employees)
{
this._employees = employees;
}
IEnumerator Members#region IEnumerator Members
public object Current
{
get
{
Console.WriteLine("EmployeeEnumerator.Current is invoked");
return this._employees[this._index];
}
}
public bool MoveNext()
{
Console.WriteLine("EmployeeEnumerator.MoveNext is invoked");
if (this._index < this._employees.Length - 1)
{
this._index++;
return true;
}
return false;
}
public void Reset()
{
this._index = -1;
}
#endregion
}
class Program
{
static void Main(string[] args)
{
Employee[] employees = new Employee[] { new Employee("0001", "Zhang San", 21), new Employee("0002", "Li Si", 30) };
EmployeeList empoyeeList = new EmployeeList();
empoyeeList.Employees = employees;
Console.WriteLine("Begin foreach loop ");
foreach (Employee employee in empoyeeList)
{
Console.WriteLine(employee.ToString());
}
Console.WriteLine("\n\nBegin while loop ");
IEnumerator enumerator = empoyeeList.GetEnumerator();
while (enumerator.MoveNext())
{