文件:form1.cs

using System;
using System.Collections.Generic;
using
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.SqlClient;

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

        private void label1_Click(object sender, EventArgs e)
        {

        }

        private void user_TextChanged(object sender, EventArgs e)
        {

        }

        private void button1_Click(object sender, EventArgs e)
        {
            data dataconn = new data();
            SqlDataReader dr = dataconn.read("select * from kankan where user = '" + this.user.Text + "' and password = '" + this.password.Text + "'");
            if (dr.HasRows)
            {
                dr.Read();
                user = dr["user"].ToString();
                dr.Close();
                MessageBox.Show("已经查到了，这是真的");
            }
            else
            {
                MessageBox.Show("哎，你的账号或者是密码有错误哦");
            }
            dr.Close();

        }
    }
}





##################################################

文件名：data.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.Data.SqlClient;

namespace like
{
    class data
    {
        private string connstr = "server=.;user id=sa;pwd=;database=kankan";
        public SqlDataReader read(string str)
        {
            SqlConnection conn = new SqlConnection(connstr);
            conn.Open();
            SqlCommand cmd = new SqlCommand(str, conn);
            SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
            return dr;
        }
    }
}

执行的时候，提示缺少调试目标，然后就是请生成项目并重试，或者相应的设置outputpath和Assemblyname属性，使其指向目标程序集的正确位置

类data没有构造函数，还有结束后dr.close()的方式不好，还有要关闭数据库连接.

解决方案--->右键--->属性--->配置属性--->项目like--->生成 复选框 勾上