从 C# 对象创建数据读取器

Question

I am having trouble with the following line:

MySqlDataReader DataReader = objDatabase.SetCommandType("GetRaceLevels").ExecuteReader();

It keeps returning the following error:

System.InvalidOperationException: 'Connection must be valid and open.'

private void RegisterForm_Load(object sender, EventArgs e)
        {

            HideMe();
            MoveMe(-180);

            MySqlConnection myConnection = objDatabase.GetConnection(); //must save the object based connection to a local variable for some reason.

            myConnection.Open();
            MySqlDataReader DataReader = objDatabase.SetCommandType("GetRaceLevels").ExecuteReader();

            try
            {
                while (DataReader.Read())
                {
                    cboRunnerTypes.Items.Add(DataReader[1]);
                }

            }
            catch (Exception ex)
            {
                MessageBox.Show("Critical error!");
            }
            myConnection.Close();
        }

I have tested the connection, it does work just fine, and it works during my login process.

The only other thing is this whole process utilises my clsDatabase class, that is where MySqlDataReader DataReader = objDatabase.SetCommandType("GetRaceLevels").ExecuteReader(); comes from.

This is the function on the clsDatabse class:

public MySqlCommand SetCommandType(string sProcedureName)
        {
            MySqlCommand myCommand = new MySqlCommand(sProcedureName, GetConnection()); //I think the problem is here, how am I fixing it though?
            myCommand.CommandType = CommandType.StoredProcedure;
            return myCommand;
        }

I hope this all makes sense and I am not being extremely thick. Any help would be much appreciated! Thank you!

EDIT: The class:

class clsDatabase
    {
        private const string conString = "server = ; database = ; user = ; password = ; charset = utf8";
        public MySqlConnection GetConnection()
        {
            MySqlConnection myConnection = new MySqlConnection(conString);
            return myConnection;
        }

        public void EmailCommandCaller(MySqlCommand myCommand, string sEmail, string sContent)
        {
            myCommand.CommandType = CommandType.StoredProcedure;
            myCommand.Parameters.AddWithValue(sEmail, sContent);
        }

        public void LoginCommandCaller(MySqlCommand myCommand, string sEmail, string sPassword, string sEmailContent, string sPasswordConetnt)
        {
            myCommand.CommandType = CommandType.StoredProcedure;
            myCommand.Parameters.AddWithValue(sEmail, sEmailContent);
            myCommand.Parameters.AddWithValue(sPassword, sPasswordConetnt);
        }
        public MySqlCommand SetCommandType(string sProcedureName)
        {
            MySqlCommand myCommand = new MySqlCommand(sProcedureName, GetConnection()); //I think the problem is here, how am I fixing it though?
            myCommand.CommandType = CommandType.StoredProcedure;
            return myCommand;
        }
    }

Answer 1

Everytime you call GetConnection() you're getting a brand new one. A new connection starts closed. Now, look at your SetCommandType method. It's instancianting a new MySqlCommand with a brand new connection, which is closed. You could open the connection in the method, but that is error prone, as you would end up with no means to close the connection afterward. Instead, instantiate the connection where you want to use it. Also, use using statements for better IDisposable handling.

private void RegisterForm_Load(object sender, EventArgs e)
{
    HideMe();
    MoveMe(-180);
    using(MySqlConnection myConnection = new MySqlConnection(conString)){
        myConnection.Open();
        MySqlCommand myCommand = new MySqlCommand("GetRaceLevels", myConnection); 
        myCommand.CommandType = CommandType.StoredProcedure;
        using(MySqlDataReader DataReader = myCommand.ExecuteReader()){
            try
            {
                while (DataReader.Read())
                {
                    cboRunnerTypes.Items.Add(DataReader[1]);
                }

            }
            catch (Exception ex)
            {
                MessageBox.Show("Critical error!");
            }
        }               
    }
}