用法一 this代表当前类的实例对象
namespace Demo{ public class Test { private string scope = "全局变量"; public string getResult() { string scope = "局部变量"; // this代表Test的实例对象 // 所以this.scope对应的是全局变量 // scope对应的是getResult方法内的局部变量 return this.scope + "-" + scope; } } class Program { static void Main(string[] args) { try { Test test = new Test(); Console.WriteLine(test.getResult()); } catch (Exception ex) { Console.WriteLine(ex); } finally { Console.ReadLine(); } } }} 用法二 用this串联构造函数
namespace Demo{ 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"); } } class Program { static void Main(string[] args) { try { Test test = new Test("张三"); } catch (Exception ex) { Console.WriteLine(ex); } finally { Console.ReadLine(); } } }} 用法三 为原始类型扩展方法
namespace Demo{ public static class Extends { // string类型扩展ToJson方法 public static object ToJson(this string Json) { return Json == null ? null : JsonConvert.DeserializeObject(Json); } // object类型扩展ToJson方法 public static string ToJson(this object obj) { var timeConverter = new IsoDateTimeConverter { DateTimeFormat = "yyyy-MM-dd HH:mm:ss" }; return JsonConvert.SerializeObject(obj, timeConverter); } public static string ToJson(this object obj, string datetimeformats) { var timeConverter = new IsoDateTimeConverter { DateTimeFormat = datetimeformats }; return JsonConvert.SerializeObject(obj, timeConverter); } public static T ToObject (this string Json) { return Json == null ? default(T) : JsonConvert.DeserializeObject (Json); } public static List ToList (this string Json) { return Json == null ? null : JsonConvert.DeserializeObject >(Json); } public static DataTable ToTable(this string Json) { return Json == null ? null : JsonConvert.DeserializeObject (Json); } public static JObject ToJObject(this string Json) { return Json == null ? JObject.Parse("{}") : JObject.Parse(Json.Replace(" ", "")); } } class Program { static void Main(string[] args) { try { List users = new List { new User{ID="1",Code="zs",Name="张三"}, new User{ID="2",Code="ls",Name="李四"} }; // list转化json字符串 string json = users.ToJson(); // string转化List users = json.ToList (); // string转化DataTable DataTable dt = json.ToTable(); } catch (Exception ex) { Console.WriteLine(ex); } finally { Console.ReadLine(); } } } public class User { public string ID { get; set; } public string Code { get; set; } public string Name { get; set; } }}
用法四 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{ /// /// EPList 支持为List创建索引 /// /// 类型 public class EPList { #region 成员变量 /// /// 索引 /// private List m_Index = new List (); /// /// 缓存数据 /// private Dictionary > m_CachedData = new Dictionary >(); /// /// List数据源 /// private List m_ListData = new List (); /// /// 通过索引值取数据 /// /// 索引字段 /// 字段值 /// this[string[] indexFields] { get { string key = string.Join(",", indexFields); if (m_CachedData.ContainsKey(key)) return m_CachedData[key]; return new List (); } } #endregion #region 公共方法 /// /// 创建索引 /// /// 索引字段 public void CreateIndex(string[] indexFields) { if (m_Index.Contains(indexFields)) return; m_Index.Add(indexFields); } /// /// 添加 /// /// 记录 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 list = new List { record }; m_CachedData.Add(key, list); } }); } #endregion #region 私有方法 /// /// 获取值 /// /// 记录 /// 字段名 /// /// 获取Key /// /// 记录 /// 索引字段 private string getKey(T record, string[] indexFields) { List values = new List (); foreach (var field in indexFields) { string value = Convert.ToString(getValue(record, field)); values.Add(field + ":" + value); } return string.Join(",", values); } /// /// 获取Key /// /// 索引字段 /// 字段值 /// 给EPList创建索引，并添加数据
private EPListGetEPListData(){ EPList eplist = new EPList (); 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;}
通过索引高效查询数据
////// 获取子节点/// /// /// private IEnumerableCreateChildren(EPList data, TreeInfo node){ string id = node == null ? "0" : node.id; List childNodes = new List (); // 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);}