using的几种用途

using 常用来引用命名空间

using System;
using System.Data;
using System.Data.SqlClient;
using System.Collections.Generic;
using Model;
using IDAL;
using DBUnititly;

using另一个用途是给类和命名空间指定别名

using  spacename = system.io

using system
using Introduction = system.text;
class Test
(
publ ic static int Main()
(
Introduction::NamespaceEXample NS=new Introduction::NamespaceExample()
Console.WriteLine(NS.GetNamespace());
return 0;
)

using还有一个用途是自动帮你释放资源

 public DataSet Sedd()
        {
            DataSet ds = new DataSet();
            using (SqlConnection sqlconntion = new SqlConnection(connectionstring))
            {
                sqlconntion.Open();
                using (SqlCommand sqlcomm = new SqlCommand("select * from users",sqlconntion))
                {
                    SqlDataAdapter dad = new SqlDataAdapter();
                    dad.SelectCommand = sqlcomm;
                    dad.Fill(ds);
                   
                }
            }
            return ds; 
        }