“System.InvalidOperationException”类型的未经处理的异常出现在 MySql.Data.dll 中。


  //创建数据库连接的函数
        public MySqlConnection GetConn()
        {
            string connString = "server=localhost;username=root;password=111222333;database=csf";
            MySqlConnection conn = new MySqlConnection(connString);
            
            try
            {
                conn.Open();
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.ToString());
            }
            return conn;
        }
private void button1_Click(object sender, EventArgs e)
        {
            if (textBox1.Text==""||textBox2.Text=="")
            {
                MessageBox.Show("用户名或密码不能为空");
                return;
            }
            else
            {
                MySqlConnection conn = GetConn();
                MySqlCommand cmd1 = new MySqlCommand("select username,userpassword from userInfo where username='" +
                                                     textBox1.Text.Trim()+ "' and userpassword='" + textBox2.Text.Trim() + "'",conn);
                conn.Open(); //显示错误
                MySqlDataReader dr = cmd1.ExecuteReader();
                while(dr.Read())
                {
                    login _instance=new login();
                    userName = textBox1.Text;
                    string password = textBox2.Text;
                    this.Visible = false;
                    MessageBox.Show("登陆成功");
                    mainCenter mc=new mainCenter();
                    mc.Show();                    conn.Close();
                    return;
                }                if (dr.Read() == false)
                {
                    conn.Close();
                    MessageBox.Show("用户名或密码不正确");
                }
            }
        }