c# winform display database data from combobox selection

Question

I have a check button that will fetch the month and year in combo box:

private void cmdSend_Click(object sender, System.EventArgs e)
    {
        List<string>[] list;
        list = dbConnect.Select(month_list.SelectedItem.ToString(), year_list.SelectedItem.ToString());

        printer_info.Rows.Clear();
        for (int i = 0; i < list[0].Count; i++)
        {
            int number = printer_info.Rows.Add();
            printer_info.Rows[number].Cells[0].Value = list[0][i];
            printer_info.Rows[number].Cells[1].Value = list[1][i];
            printer_info.Rows[number].Cells[2].Value = list[2][i];
            printer_info.Rows[number].Cells[3].Value = list[3][i];
        }
    }

enter image description here

The check button then pass the month and year to the select statement function:

public List<string>[] Select(string month,string year)
    {
        string query = "SELECT * FROM page_counter WHERE month = '@month' AND year = @year;";

        //Create a list to store the result
        List<string>[] list = new List<string>[4];
        list[0] = new List<string>();
        list[1] = new List<string>();
        list[2] = new List<string>();
        list[3] = new List<string>();

        //Open connection
        if (this.OpenConnection() == true)
        {
            //Create Command
            MySqlCommand cmd = new MySqlCommand(query, connection);
            cmd.Parameters.Add("@month",MySqlDbType.VarChar);
            cmd.Parameters.Add("@year", MySqlDbType.Year);
            cmd.Parameters["@month"].Value = month;
            cmd.Parameters["@year"].Value = year;

            //Create a data reader and Execute the command
            MySqlDataReader dataReader = cmd.ExecuteReader();

            //Read the data and store them in the list
            while (dataReader.Read())
            {
                list[0].Add(dataReader["id"].ToString() + "");
                list[1].Add(dataReader["month"].ToString() + "");
                list[2].Add(dataReader["year"].ToString() + "");
                list[3].Add(dataReader["page_count"].ToString() + "");
            }

            //close Data Reader
            dataReader.Close();

            //close Connection
            this.CloseConnection();

            //return list to be displayed
            return list;
        }

the data will then display on the gridview where all column are specified by default in page designer:
enter image description here

When I run the code, it doesnt have any error, but theres no value display on the gridview. Is there any mistake I make? Im newbie in c# winform,please advise.

As far as I can see, you don't set the DataSource of dataGridView.And why you are using a List<string>[] ? use a class with 4 properties instead. — Selman Genç
– Selman Genç, Commented Mar 11, 2014 at 0:35

Selman Genç · Accepted Answer · 2014-03-11 00:46:55Z

1

I think you have two mistakes.First you should remove the single-quotes from query string:

string query = "SELECT * FROM page_counter WHERE month = @month AND year = @year;"

Because when you use single-quotes your parameter names treated as actual value.Secondly, I would highly recommend you to use a class for your item instead of a List<string>[].The class would look like this:

public class Data
{
    public int Id { get; set; }
    public string Month { get; set; }
    public string Year { get; set; }
    public int PageCount { get; set; }
}

Then create a List<Data> and populate it like this:

 var dataList = new List<Data>();
 while (dataReader.Read())
 {
    var item = new Data();
    item.Id = Convert.Toınt32(dataReader["id"]);
    item.Month = dataReader["month"].ToString();
    item.Year = dataReader["year"].ToString();
    item.PageCount = Convert.ToInt32(dataReader["page_count"]);
    dataList.Add(item);
}
return dataList;

Then ofcourse change the returning type of your method:

public List<Data> Select(string month,string year)

Then all you need to do is set the DataSource property:

var list = dbConnect.Select(month_list.SelectedItem, year_list.SelectedItem);
printer_info.DataSource = list;

answered Mar 11, 2014 at 0:46

Selman Genç

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Ren Over a year ago

Where should I create the List<Data>? Is it in the public class Data?

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