在List范型集合中实现自定义条件复杂查询

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

namespace ListDemo
{
/// <summary>
/// 首发地址：http://blog.csdn.net/zhoufoxcn
/// 大类别
/// </summary>
public class CatalogInfo
{
private int catalogId;
private string catalogName;

public string CatalogName
{
get { return catalogName; }
set { catalogName = value; }
}

public int CatalogId
{
get { return catalogId; }
set { catalogId = value; }
}

public CatalogInfo(int catalogId, string catalogName)
{
this.catalogId = catalogId;
this.catalogName = catalogName;
}

}
}

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

namespace ListDemo
{
/// <summary>
/// 首发地址：http://blog.csdn.net/zhoufoxcn
/// 查找符合特定条件的CatalogInfo类
/// </summary>
public class CatalogFinder
{
private int catalogId;

public int CatalogId
{
get { return catalogId; }
set { catalogId = value; }
}

public CatalogFinder()
{
}

public CatalogFinder(int catalogId)
{
this.catalogId = catalogId;
}
/// <summary>
/// 符合Predicate>T< match的方法
/// </summary>
/// <param name="info"></param>
/// <returns></returns>
public bool FindByCatalogId(CatalogInfo info)
{
return info.CatalogId == catalogId;
}
}
}

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

namespace ListDemo
{
/// <summary>
/// 首发地址：http://blog.csdn.net/zhoufoxcn
/// 小类别
/// </summary>
public class BoardInfo
{
private int boardId;
private string boardName;
private int catalogId;
/// <summary>
/// 所在大类别编号
/// </summary>
public int CatalogId
{
get { return catalogId; }
set { catalogId = value; }
}

public string BoardName
{
get { return boardName; }
set { boardName = value; }
}

public int BoardId
{
get { return boardId; }
set { boardId = value; }
}

public BoardInfo(int boardId, string boardName, int catalogId)
{
this.boardId = boardId;
this.boardName = boardName;
this.catalogId = catalogId;
}

}
}
上面分别是两个范型集合中用到的实体，以及将来要用于查找这些实体的辅助类，下面距离说明用法：

using System;
using System.Collections.Generic;
using System.Drawing.Imaging;
using ListDemo;

/// <summary>
/// 说明：在List<T>范型集合中提供了一类委托，以确定要寻找集合中的哪些符合条件的单个元素或者集合
/// msdn里描述如下：Predicate 委托，用于定义要搜索的元素应满足的条件。
/// 这一点msdn帮助里面说得很简单，只以List<string>范型集合为例说了一些简单应用，这些完全不能满足
/// 一些复杂的应用，比如查找集合中符合某些特性的单个元素或者元素集合，因为Predicate 委托只能使用
/// 一个参数，写本文的目的就是说明如何满足复杂的要求在范型集合中查找元素
/// 作者：周公
/// 日期：2007-12-28
/// 首发地址：http://blog.csdn.net/zhoufoxcn
/// </summary>
public class Example
{
public static void Main()
{
//初始化大类别集合
List<CatalogInfo> catalogList = new List<CatalogInfo>(10);
for (int i = 0; i <10; i++)
{
catalogList.Add(new CatalogInfo(i, "大类别" + i));
}

//初始化小类别集合，随机指定它们的大类别编号
List<BoardInfo> boardList = new List<BoardInfo>(50);
Random random=new Random(100);
for (int i = 0; i < 100; i++)
{
boardList.Add(new BoardInfo(i, "小类别" + i, random.Next() % 10));
}
Console.WriteLine("=======在大类别中查找========");
CatalogFinder catalogFinder = new CatalogFinder(5);
CatalogInfo catalogInfo = catalogList.Find(catalogFinder.FindByCatalogId);
Console.WriteLine("该大类别的名称：" + catalogInfo.CatalogName);

Console.WriteLine("=======在小类别中查找========");
BoardFinder boardFinder = new BoardFinder();
boardFinder.BoardId = 25;
BoardInfo boardInfo = boardList.Find(boardFinder.FindByBoardId);
Console.WriteLine("该小类别信息：小类别名称{0},所属大类别编号{1}", boardInfo.BoardName, boardInfo.CatalogId);

Console.WriteLine("=======在小类别中按大类别编号查找========");
boardFinder.CatalogId = 9;
List<BoardInfo> boardInfoList = boardList.FindAll(boardFinder.FindByCatalogId);
foreach (BoardInfo info in boardInfoList)
{
Console.WriteLine("该小类别信息：小类别名称{0},所属大类别编号{1}", info.BoardName, info.CatalogId);
}

Console.ReadLine();
}
}以下是输出结果：