.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);
        }
    }

}