C#中SqlDataAdapter 适配器 获取数据库中的数据

using System;
 using System.Collections.Generic;
using System.ComponentModel;
 using System.Configuration;
 using System.Data;
using System.Data.SqlClient;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using System.Windows.Forms;

namespace DataSetDome
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void btnGetData_Click(object sender, EventArgs e)
        {
            String connStr = ConfigurationManager.ConnectionStrings["sqlConn"].ConnectionString;

            using (SqlConnection connSql = new SqlConnection(connStr))//建立连接对象
            {
                string strSql = "select UserID,UserName,UserPwd from UserInfo";

                //创建一个适配器类
                //方式二：SqlDataAdapter adapter1 = new SqlDataAdapter(strSql, connStr);
                using (SqlDataAdapter adapter = new SqlDataAdapter(strSql,connSql))
                {
                    //DataSet dt = new DataSet();
                    DataTable dt = new DataTable();//填充DataTable
                    //填充之前，不需要打开数据库连接，Adapter会自动打开连接，并执行sql

                    //Fill方法内部：
                        //1、先判断SqlConnection 是否初始化 ，如果没有就先打开连接
                        //2、初始化一个Select   SqlCommand对象
                        //3、通过cmd对象执行一下，返回SqlDataReader对象
                        //4、读取数据库中的数据，填充到内存表中去
                    adapter.Fill(dt);//读取数据库中的数据 填充到内存表中
                    adapter.Fill(new DataSet(), "s");//DataSet一次可以读取多张表的数据
                    List<UseInfo> userList = new List<UseInfo>();
                    foreach (DataRow item in dt.Rows)
                    {
                        userList.Add(new UseInfo() { UserId = item["UserID"].ToString(), UserName = item["UserName"].ToString(), UserPwd = item["UserPwd"].ToString()});
                    }
                    this.dataGridView1.DataSource = userList;
                }
            }
        }
    }
}


private void button2_Click(object sender, EventArgs e)
        {
            string connStr = ConfigurationManager.ConnectionStrings["sqlConn"].ConnectionString;
            string strSql = "select UserID,UserName,UserPwd from UserInfo2";

            //创建一个适配器类
            //方式二：SqlDataAdapter adapter1 = new SqlDataAdapter(strSql, connStr);
            using (SqlDataAdapter adapter1 = new SqlDataAdapter(strSql, connStr))
            {
                // List<UseInfo> dt_list = this.dataGridView1.DataSource as List<UseInfo>;
                DataTable dt = this.dataGridView1.DataSource as DataTable;
                // UserID,UserName,UserPwd
                //DataColumn dcId = new DataColumn("UserID", typeof(string));
                //DataColumn dcName = new DataColumn("UserName", typeof(string));
                //DataColumn dcPwd = new DataColumn("UserPwd", typeof(string));
                //dt.Columns.AddRange(new DataColumn[] { dcId, dcName, dcPwd });

                //foreach (UseInfo item in dt_list)
                //{
                //    dt.Rows.Add(item.UserId, item.UserName, item.UserPwd);
                //}
                //SqlCommandBuilder 帮助我们的Adapter生成相关的CRUD SqlCommand
                using (SqlCommandBuilder scb = new SqlCommandBuilder(adapter1))
                {
                    adapter1.Update(dt);
                }
            }
        }