c# this关键字用法

 1 /// <summary>
 2     /// 扩展类 用于为原始类扩展方法  
 3     /// </summary>
 4    public static class AM_Extends
 5     {
 6         /// <summary>
 7         /// 为string类扩展了一个child方法，实现某功能
 8         /// </summary>
 9         /// <param name="str"></param>
10         /// <param name="new_str"></param>
11         public static void Child( this string str,string new_str)
12         {
13             object obj = str;
14             str=new_str;
15         }
16     }

1 private void Form1_Load(object sender, EventArgs e)
2         {
3             string st1 = "123";
4             string st2 = "";
5             string st3 = "";
6             st3 = st2.Child(st1);//st3的值为“123”
7         }

 1    public class Test
 2     {
 3         public Test()
 4         {
 5             Console.WriteLine("无参构造函数");
 6         }
 7         // this()对应无参构造方法Test()
 8 　　　　 // 先执行Test()，后执行Test(string text)
 9         public Test(string text) : this()
10         {
11             Console.WriteLine(text);
12             Console.WriteLine("有参构造函数");
13         }
14     }

  1 using System;
  2 using System.Collections.Generic;
  3 using System.Linq;
  4 using System.Reflection;
  5 using System.Text;
  6 
  7 namespace MyDemo.Web
  8 {
  9     /// <summary>
 10     /// EPList 支持为List创建索引
 11     /// </summary>
 12     /// <typeparam name="T">类型</typeparam>
 13     public class EPList<T>
 14     {
 15         #region 成员变量
 16 
 17         /// <summary>
 18         /// 索引
 19         /// </summary>
 20         private List<string[]> m_Index = new List<string[]>();
 21 
 22         /// <summary>
 23         /// 缓存数据
 24         /// </summary>
 25         private Dictionary<string, List<T>> m_CachedData = new Dictionary<string, List<T>>();
 26 
 27         /// <summary>
 28         /// List数据源
 29         /// </summary>
 30         private List<T> m_ListData = new List<T>();
 31 
 32         /// <summary>
 33         /// 通过索引值取数据
 34         /// </summary>
 35         /// <param name="indexFields">索引字段</param>
 36         /// <param name="fieldValues">字段值</param>
 37         /// <returns></returns>
 38         public List<T> this[string[] indexFields]
 39         {
 40             get
 41             {
 42                 string key = string.Join(",", indexFields);
 43                 if (m_CachedData.ContainsKey(key)) return m_CachedData[key];
 44                 return new List<T>();
 45             }
 46         }
 47 
 48         #endregion
 49 
 50         #region 公共方法
 51 
 52         /// <summary>
 53         /// 创建索引
 54         /// </summary>
 55         /// <param name="indexFields">索引字段</param>
 56         public void CreateIndex(string[] indexFields)
 57         {
 58             if (m_Index.Contains(indexFields)) return;
 59             m_Index.Add(indexFields);
 60         }
 61 
 62         /// <summary>
 63         /// 添加
 64         /// </summary>
 65         /// <param name="record">记录</param>
 66         public void Add(T record)
 67         {
 68             m_ListData.Add(record);
 69             m_Index.ForEach(indexFields =>
 70             {
 71                 string key = getKey(record, indexFields);
 72                 if (m_CachedData.ContainsKey(key))
 73                 {
 74                     m_CachedData[key].Add(record);
 75                 }
 76                 else
 77                 {
 78                     List<T> list = new List<T> { record };
 79                     m_CachedData.Add(key, list);
 80                 }
 81             });
 82         }
 83 
 84         #endregion
 85 
 86         #region 私有方法
 87 
 88         /// <summary>
 89         /// 获取值
 90         /// </summary>
 91         /// <param name="record">记录</param>
 92         /// <param name="fieldName">字段名</param>
 93         /// <returns></returns>
 94         private object getValue(T record, string fieldName)
 95         {
 96             Type type = typeof(T);
 97             PropertyInfo propertyInfo = type.GetProperty(fieldName);
 98             return propertyInfo.GetValue(record, null);
 99         }
100 
101         /// <summary>
102         /// 获取Key
103         /// </summary>
104         /// <param name="record">记录</param>
105         /// <param name="indexFields">索引字段</param>
106         private string getKey(T record, string[] indexFields)
107         {
108             List<string> values = new List<string>();
109             foreach (var field in indexFields)
110             {
111                 string value = Convert.ToString(getValue(record, field));
112                 values.Add(field + ":" + value);
113             }
114             return string.Join(",", values);
115         }
116 
117         /// <summary>
118         /// 获取Key
119         /// </summary>
120         /// <param name="indexFields">索引字段</param>
121         /// <param name="fieldValues">字段值</param>
122         /// <returns></returns>
123         private string getKey(string[] indexFields, object[] fieldValues)
124         {
125             if (indexFields.Length != fieldValues.Length) return string.Empty;
126             for (int i = 0; i < indexFields.Length; i++)
127             {
128                 fieldValues[i] = indexFields[i] + ":" + fieldValues[i];
129             }
130             string key = string.Join(",", fieldValues);
131             return key;
132         }
133 
134         #endregion
135     }
136 }

 1 private EPList<SysDepartInfo> GetEPListData()
 2 {
 3     EPList<SysDepartInfo> eplist = new EPList<SysDepartInfo>();
 4     eplist.CreateIndex(new string[] { "ParentId" });
 5     string sql = "select Id,ParentId,Code,Name from SysDepart";
 6     SqlHelper.ExecuteReader(sql, null, (reader) =>
 7     {
 8         SysDepartInfo record = new SysDepartInfo();
 9         record.Id = Convert.ToString(reader["Id"]);
10         record.ParentId = Convert.ToString(reader["ParentId"]);
11         record.Code = Convert.ToString(reader["Code"]);
12         record.Name = Convert.ToString(reader["Name"]);
13         eplist.Add(record);
14     });
15     return eplist;
16 }

 1 /// <summary>
 2 /// 获取子节点
 3 /// </summary>
 4 /// <param name="data"></param>
 5 /// <param name="parentId"></param>
 6 private IEnumerable<TreeInfo> CreateChildren(EPList<SysDepartInfo> data, TreeInfo node)
 7 {
 8     string id = node == null ? "0" : node.id;
 9     List<TreeInfo> childNodes = new List<TreeInfo>();
10     // 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
11     var indexValues = new string[] { "ParentId:" + id };
12     var childData = data[indexValues];
13     childData.ForEach(record =>
14     {
15         var childNode = new TreeInfo
16         {
17             id = record.Id,
18             text = record.Code + " " + record.Name
19         };
20         childNodes.Add(childNode);
21         childNode.children = CreateChildren(data, childNode);
22     });
23     return childNodes.OrderBy(record => record.text);
24 }