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

以上就是小编整理的全部相关知识点内容，感谢大家的学习和对的支持。