Question

以下代码在if-else语句中显示消息框后抛出异常。例外情况是我的读者无法阅读，因为它已关闭：

try
{
    using (MySqlConnection conn = new MySqlConnection(Config.ConnectionString()))
    {
        conn.Open();
        MySqlCommand cmd = new MySqlCommand("SELECT * from tb_useraccounts;", conn);
        MySqlDataReader dr = cmd.ExecuteReader();

        while (dr.Read())
        {
            if (UserName == (dr["username"].ToString()) && PassWord == (dr["password"].ToString()))
            {
                frmMain main = new frmMain();
                main.Show();
                login.Hide();
            }
            else if (UserName == string.Empty || PassWord == string.Empty)
            {
                MessageBox.Show("Please fill the blank spaces!");
            }
            else
            {
                MessageBox.Show("The username and password you inserted is incorrect!");
            }
            dr.Close();
            conn.Close();
        }
    }

如何让while循环正常工作？

Answer 1

你必须在while循环之后关闭阅读器和连接，如下所示

try
   {
   using (MySqlConnection conn = new MySqlConnection(Config.ConnectionString()))
        {
         conn.Open();
    MySqlCommand cmd = new MySqlCommand("SELECT * from tb_useraccounts;", conn);
    MySqlDataReader dr = cmd.ExecuteReader();

     while (dr.Read())
     {
        if (UserName == (dr["username"].ToString()) && PassWord == (dr["password"].ToString()))
                    {
                        frmMain main = new frmMain();
                        main.Show();
                        login.Hide();
                    }
                    else if (UserName == string.Empty || PassWord == string.Empty)
                    {
                        MessageBox.Show("Please fill the blank spaces!");
                    }
                    else
                    {
                        MessageBox.Show("The username and password you inserted is incorrect!");
                    }
                }
                    dr.Close();
                    conn.Close();
            }

如何使用while（datareader.Read（））

1 个答案: