.NET常用设计模式——迭代器模式

迭代器模式(Iterator)

• 封装多个元素
• 使用户正确使用
• 遍历内部内容

总结Iterator

• 使用标准接口遍历列表/集合
• 封装操作
• 提供后期操功能作扩展

应用实例

using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections;

namespace CSDesingPattern
{
    public class Employee
    {
        private int EmpId = 0;
        private string EmpName = "";

        public int ID
        {
            get
            {
                return EmpId;
            }
            set
            {
                EmpId = value;
            }
        }
        public string Name
        {
            get
            {
                return EmpName;
            }
            set
            {
                EmpName = value;
            }
        }
    }

    //集合类
    public class Employees
    {
        private ArrayList arEmp = new ArrayList();
        private int EmpCount;

        public Employees()
        {

            SqlConnection cn = new SqlConnection
                ("server=localhost;database=northwind;uid=sa;pwd=windows");
            SqlCommand cmd = new SqlCommand
                ("select EmployeeID,FirstName,BirthDate from Employees", cn);
            cn.Open();
            SqlDataReader dr = cmd.ExecuteReader();

            while (dr.Read())
            {
                Employee obj = new Employee();
                obj.ID = dr.GetInt32(0);
                obj.Name = dr.GetString(1);
                arEmp.Add(obj);
            }

            EmpCount = arEmp.Count;
        }

        public Employee Item(int idx)
        {
            return (Employee)arEmp[idx];
        }

        public int Count
        {
            get
            {
                return EmpCount;
            }
        }
    }

    //迭代器实现类
    public class EmployeesIterator
    {
        private int intCurrent;
        private Employees mObj;

        public EmployeesIterator(ref Employees obj)
        {

            intCurrent = 0;
            mObj = obj;
        }

        public Employee MoveFirst()
        {
            intCurrent = 0;

            return mObj.Item(intCurrent);
        }
        public Employee MoveLast()
        {
            intCurrent = mObj.Count - 1;

            return mObj.Item(intCurrent);
        }
        public Employee MoveNext()
        {
            intCurrent = intCurrent + 1;
            if (intCurrent >= mObj.Count)
            {
                intCurrent = mObj.Count - 1;

                throw new Exception("索引超过下限");
            }
            return mObj.Item(intCurrent);
        }

        public Employee MovePrev()
        {
            //throw new Exception (intCurrent.ToString());
            intCurrent = intCurrent - 1;

            if (this.intCurrent == -1)//||this.intCurrent <=0) 
            {
                intCurrent = 1;
                throw new Exception("索引超过上限,当前为" + intCurrent.ToString());
            }
            return mObj.Item(intCurrent);
        }
    }

}