Display a 'string' from 'System.Data.OleDb.OleDbDataReader'. Access Database to C# Form

Question

Trying to display a value from Access Database to display onto ListBox on a form. The previous form sends this form a string which is 'prevval'- for reference to the code. Not entirely sure what the issue is? Please Help!! The QuestionID is technically a number but is it an issue if im making it a string because its being presented on the ListBox?

Error System.Data.OleDb.OleDbException (0x80040E10): No value given for one or more required parameters

Code:

       try
        {
            connection.Open();
            OleDbCommand command = new OleDbCommand();
            command.Connection = connection;
            string query = "SELECT QuestionID FROM tblQuestions WHERE (Topic='" + prevval + "')";
            command.CommandText = query;
            OleDbDataReader reader = command.ExecuteReader();
            while (reader.Read())
            {
                listQuestions.Items.Add(reader.ToString());
            }
            connection.Close();
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error " + ex);
        }

Answer 1

尝试这个

listQuestions.Items.Add(reader["QuestionID"].ToString());