using的几种用途

using 常用来引用命名空间

1 using System;
2 using System.Data;
3 using System.Data.SqlClient;
4 using System.Collections.Generic;
5 using Model;
6 using IDAL;
7 using DBUnititly;

using另一个用途是给类和命名空间指定别名

 1 using  spacename = system.io
 2
 3 using system
 4 using Introduction = system.text;
 5 class Test
 6 (
 7 publ ic static int Main()
 8 (
 9 Introduction::NamespaceEXample NS=new Introduction::NamespaceExample()
10 Console.WriteLine(NS.GetNamespace());
11 return 0;
12 )

using还有一个用途是自动帮你释放资源

 1  public DataSet Sedd()
 2         {
 3             DataSet ds = new DataSet();
 4             using (SqlConnection sqlconntion = new SqlConnection(connectionstring))
 5             {
 6                 sqlconntion.Open();
 7                 using (SqlCommand sqlcomm = new SqlCommand("select * from users",sqlconntion))
 8                 {
 9                     SqlDataAdapter dad = new SqlDataAdapter();
10                     dad.SelectCommand = sqlcomm;
11                     dad.Fill(ds);
12
13                 }
14             }
15             return ds;
16         }