c# this关键字用法代码详解
作者:inner_cosmos 时间:2022-06-07 15:22:09
用法1 为原始类型扩展方法
先说一下,this 后面跟的类型,就是要拓展方法的类型。注意要写在静态类中的静态方法,不然有些情况下访问
/// <summary>
/// 扩展类 用于为原始类扩展方法
/// </summary>
public static class AM_Extends
{
/// <summary>
/// 为string类扩展了一个child方法,实现某功能
/// </summary>
/// <param name="str"></param>
/// <param name="new_str"></param>
public static void Child( this string str,string new_str)
{
object obj = str;
str=new_str;
}
}
定义扩展方法
private void Form1_Load(object sender, EventArgs e)
{
string st1 = "123";
string st2 = "";
string st3 = "";
st3 = st2.Child(st1);//st3的值为“123”
}
调用实例
用法2 this代表当前类的实例对象
用法3 用this串联构造函数
public class Test
{
public Test()
{
Console.WriteLine("无参构造函数");
}
// this()对应无参构造方法Test()
// 先执行Test(),后执行Test(string text)
public Test(string text) : this()
{
Console.WriteLine(text);
Console.WriteLine("有参构造函数");
}
}
用法4 索引器(基于索引器封装EPList,用于优化大数据下频发的Linq查询引发的程序性能问题,通过索引从list集合中查询数据)
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
using System.Text;
namespace MyDemo.Web
{
/// <summary>
/// EPList 支持为List创建索引
/// </summary>
/// <typeparam name="T">类型</typeparam>
public class EPList<T>
{
#region 成员变量
/// <summary>
/// 索引
/// </summary>
private List<string[]> m_Index = new List<string[]>();
/// <summary>
/// 缓存数据
/// </summary>
private Dictionary<string, List<T>> m_CachedData = new Dictionary<string, List<T>>();
/// <summary>
/// List数据源
/// </summary>
private List<T> m_ListData = new List<T>();
/// <summary>
/// 通过索引值取数据
/// </summary>
/// <param name="indexFields">索引字段</param>
/// <param name="fieldValues">字段值</param>
/// <returns></returns>
public List<T> this[string[] indexFields]
{
get
{
string key = string.Join(",", indexFields);
if (m_CachedData.ContainsKey(key)) return m_CachedData[key];
return new List<T>();
}
}
#endregion
#region 公共方法
/// <summary>
/// 创建索引
/// </summary>
/// <param name="indexFields">索引字段</param>
public void CreateIndex(string[] indexFields)
{
if (m_Index.Contains(indexFields)) return;
m_Index.Add(indexFields);
}
/// <summary>
/// 添加
/// </summary>
/// <param name="record">记录</param>
public void Add(T record)
{
m_ListData.Add(record);
m_Index.ForEach(indexFields =>
{
string key = getKey(record, indexFields);
if (m_CachedData.ContainsKey(key))
{
m_CachedData[key].Add(record);
}
else
{
List<T> list = new List<T> { record };
m_CachedData.Add(key, list);
}
});
}
#endregion
#region 私有方法
/// <summary>
/// 获取值
/// </summary>
/// <param name="record">记录</param>
/// <param name="fieldName">字段名</param>
/// <returns></returns>
private object getValue(T record, string fieldName)
{
Type type = typeof(T);
PropertyInfo propertyInfo = type.GetProperty(fieldName);
return propertyInfo.GetValue(record, null);
}
/// <summary>
/// 获取Key
/// </summary>
/// <param name="record">记录</param>
/// <param name="indexFields">索引字段</param>
private string getKey(T record, string[] indexFields)
{
List<string> values = new List<string>();
foreach (var field in indexFields)
{
string value = Convert.ToString(getValue(record, field));
values.Add(field + ":" + value);
}
return string.Join(",", values);
}
/// <summary>
/// 获取Key
/// </summary>
/// <param name="indexFields">索引字段</param>
/// <param name="fieldValues">字段值</param>
/// <returns></returns>
private string getKey(string[] indexFields, object[] fieldValues)
{
if (indexFields.Length != fieldValues.Length) return string.Empty;
for (int i = 0; i < indexFields.Length; i++)
{
fieldValues[i] = indexFields[i] + ":" + fieldValues[i];
}
string key = string.Join(",", fieldValues);
return key;
}
#endregion
}
}
创建EPList
给EPList创建索引,并添加数据
private EPList<SysDepartInfo> GetEPListData()
{
EPList<SysDepartInfo> eplist = new EPList<SysDepartInfo>();
eplist.CreateIndex(new string[] { "ParentId" });
string sql = "select Id,ParentId,Code,Name from SysDepart";
SqlHelper.ExecuteReader(sql, null, (reader) =>
{
SysDepartInfo record = new SysDepartInfo();
record.Id = Convert.ToString(reader["Id"]);
record.ParentId = Convert.ToString(reader["ParentId"]);
record.Code = Convert.ToString(reader["Code"]);
record.Name = Convert.ToString(reader["Name"]);
eplist.Add(record);
});
return eplist;
}
给EPList创建索引,并添加数据
private EPList<SysDepartInfo> GetEPListData()
{
EPList<SysDepartInfo> eplist = new EPList<SysDepartInfo>();
eplist.CreateIndex(new string[] { "ParentId" });
string sql = "select Id,ParentId,Code,Name from SysDepart";
SqlHelper.ExecuteReader(sql, null, (reader) =>
{
SysDepartInfo record = new SysDepartInfo();
record.Id = Convert.ToString(reader["Id"]);
record.ParentId = Convert.ToString(reader["ParentId"]);
record.Code = Convert.ToString(reader["Code"]);
record.Name = Convert.ToString(reader["Name"]);
eplist.Add(record);
});
return eplist;
}
给EPList创建索引,并添加数据
/// <summary>
/// 获取子节点
/// </summary>
/// <param name="data"></param>
/// <param name="parentId"></param>
private IEnumerable<TreeInfo> CreateChildren(EPList<SysDepartInfo> data, TreeInfo node)
{
string id = node == null ? "0" : node.id;
List<TreeInfo> childNodes = new List<TreeInfo>();
// ParentId字段上创建了索引,所以这里就可以通过索引值直接取出下一层子节点数据,避免Linq查询引发的效率问题
var indexValues = new string[] { "ParentId:" + id };
var childData = data[indexValues];
childData.ForEach(record =>
{
var childNode = new TreeInfo
{
id = record.Id,
text = record.Code + " " + record.Name
};
childNodes.Add(childNode);
childNode.children = CreateChildren(data, childNode);
});
return childNodes.OrderBy(record => record.text);
}
通过索引高效查询数据
来源:https://www.cnblogs.com/MatureMan/p/12303347.html
标签:c#,this,关键字用法
![](/images/zang.png)
![](/images/jiucuo.png)
猜你喜欢
完美解决java读取大文件内存溢出的问题
2023-07-31 17:53:17
java代码实现MD5加密及验证过程详解
2023-09-26 02:50:45
java实现mongodb的数据库连接池
2023-11-23 14:23:09
Java聊天室之实现客户端一对一聊天功能
2022-12-28 09:23:30
![](https://img.aspxhome.com/file/2023/0/79340_0s.png)
Android Retrofit的使用详解
2022-12-11 01:28:37
java实现简单单链表
2023-10-30 09:45:46
![](https://img.aspxhome.com/file/2023/2/58722_0s.jpg)
C#任务并行Parellel.For和Parallel.ForEach
2022-04-19 22:07:58
![](https://img.aspxhome.com/file/2023/5/85685_0s.png)
Java如何实现http接口参数和返回值加密
2023-08-23 12:28:37
java模拟hibernate一级缓存示例分享
2023-06-18 08:43:55
解决Eclipse的Servers视图中无法添加Tomcat6/Tomcat7的方法
2023-03-30 22:22:27
![](https://img.aspxhome.com/file/2023/6/64806_0s.png)
解决fastjson从1.1.41升级到1.2.28后报错问题详解
2021-12-30 21:55:35
SpringBoot 内置工具类的使用
2021-08-26 11:42:21
基于C#实现的三层架构实例
2023-09-09 11:39:33
![](https://img.aspxhome.com/file/2023/2/98262_0s.png)
Java线程组与未处理异常实例分析
2021-12-01 12:21:08
SpringBoot多种自定义错误页面方式小结
2021-12-12 00:56:03
详解Idea 2019.2 安装lombok插件失效问题解决
2023-05-01 09:22:59
![](https://img.aspxhome.com/file/2023/3/64203_0s.jpg)
java JSONArray 遍历方式(2种)
2021-09-07 19:52:48
Java LinkedList实现班级信息管理系统
2021-06-27 04:00:11
![](https://img.aspxhome.com/file/2023/7/84657_0s.jpg)
Java多线程中关于join方法的使用实例解析
2023-08-22 21:47:29
逆波兰计算器(Java实现)
2021-10-18 09:45:01
![](https://img.aspxhome.com/file/2023/4/85834_0s.jpg)