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
特点：1、静态类 2、静态方法 3、第一个参数前加this
例如：public static List<T> ToList<T>(this string Json)，就是为this对应的string类型扩展类ToList()方法，调用方式 strJson.ToList();
详细扩展
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<T>(this string Json){return Json == null ? default(T) : JsonConvert.DeserializeObject<T>(Json);}public static List<T> ToList<T>(this string Json){return Json == null ? null : JsonConvert.DeserializeObject<List<T>>(Json);}public static DataTable ToTable(this string Json){return Json == null ? null : JsonConvert.DeserializeObject<DataTable>(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<User> users = new List<User>{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Listusers = json.ToList<User>();// string转化DataTableDataTable 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
{/// <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}
}
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;
}
通过索引高效查询数据
/// <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);
}
