private void BtnLogin_Click(object sender, EventArgs e)
        {
            //登录检测
            try
            {
                string dbPath = "Data Source=" + Directory.GetCurrentDirectory() + @"\data\orders.db;Version=3;Password=07762828216;";
                using ( SQLiteConnection conn = new SQLiteConnection(dbPath)) {
                    //查询是否有相应的数据
                    string uname = TxbUsername.Text.Trim();
                    string upwd = TxbPassword.Text.Trim();
                    string sql_select = "select count(0) from users where username =@uname and password =@upwd ";
                    //连接数据库
                    if (conn.State == ConnectionState.Closed)
                    {
                        conn.Open();
                    }
                    SQLiteCommand cmd = new SQLiteCommand(sql_select, conn);
                    //cmd.Parameters.Add(new SQLiteParameter("@uname", uname));
                    //cmd.Parameters.Add(new SQLiteParameter("@upwd", upwd));
                    SQLiteParameter[] paras = new SQLiteParameter[] { new SQLiteParameter("@uname", uname), new SQLiteParameter("@upwd", upwd) };
                    cmd.Parameters.AddRange(paras);
                    SQLiteDataReader reader = cmd.ExecuteReader();
                    if (reader.Read())
                    {
                        int result = Convert.ToInt16(reader.GetValue(0));
                        if (result == 0)
                        {
                            MessageBox.Show("用户名或者密码错误，请重新输入！"); 
                        }
                        else if(result == 1)
                        {
                            MessageBox.Show("登录成功！");
                        }
                        else
                        {
                            MessageBox.Show("程序出错，请不要输入奇怪的的内容！");
                            //退出软件
                            System.Environment.Exit(0);
                        }
                    }
                    //关闭数据库连接
                    reader.Close();
                    conn.Close();
                }
            }
            catch (Exception ex)
            {
               MessageBox.Show("连接数据库失败：" + ex.Message);
            }
        }