Listbox items color change

[Mekonom]

hi all..I am new on C# .My problem is I have a 1 combo box, list box and button . When I choose value on combobox it search on database nd shows on listbox. and I used OwnerDravFixed method..It works and when i change combobox value it show that some line with another colour.But I need to take this value from button click.But second time i cant call this lisbox_DrawItem method.. Any idea? here my codes

public void groupComboBox()
        {

            connection.Open();
            MySqlCommand cmd = new MySqlCommand("select Group_NO from sinif", connection);
            reader = cmd.ExecuteReader();

            if (reader.HasRows)
                while (reader.Read())
                {
                    groupcomboBox.Items.Add(reader["Group_NO"]);
                }

            connection.Close();
        }

 private void search_B_Click(object sender, EventArgs e)
        {

listbox.items.Add("car");

listbox.items.Add("plane");
}

private void groupcomboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            if (listBox1.Items.Count != 0)
                listBox1.Items.Clear();

            connection.Open();
            MySqlCommand cmd = new MySqlCommand("select Student_ID,Student_Name,Group_NO,Student_MacAdress from student INNER JOIN sinif ON student.Group_ID = sinif.Group_ID where Group_NO=(?GroupNO)", connection);

            MySqlParameter param = new MySqlParameter();

            param.ParameterName = "?GroupNO";

            param.Value = groupcomboBox.SelectedItem.ToString();

            cmd.Parameters.Add(param);

            reader = cmd.ExecuteReader();
            if (reader.HasRows)
                while (reader.Read())
                {

                    listBox1.Items.Add("" + reader["Student_Name"] + " " + reader["Group_NO"] + " " + reader["Student_MacAdress"]);

                }
            reader.Close();
            connection.Close();
        }

private void listBox1_DrawItem(object sender, System.Windows.Forms.DrawItemEventArgs e)
        {
            int delta = 5;
            Rectangle rc = new Rectangle(e.Bounds.X + delta, e.Bounds.Y + delta, e.Bounds.Width - 10, e.Bounds.Height - delta);

            //  Console.WriteLine(e.State.ToString());

            // Setup the stringformatting object
            StringFormat sf = new StringFormat();
            sf.Alignment = StringAlignment.Near;

            // Get the item text
            listBox1 = (ListBox)sender;
            string str = (string)listBox1.Items[e.Index];

         
            // Check if the item is selected

            if(listBox1.Items[e.Index].ToString().Contains("car"))
            {
                
                       
                        // Paint the item that if not selected
                        e.Graphics.FillRectangle(new SolidBrush(Color.BlueViolet), rc);
                    e.Graphics.DrawString(str, new Font("Ariel", 9), new SolidBrush(Color.Black), rc, sf);
                    e.DrawFocusRectangle();
                
            }
            else
            {
                // Paint the item accordingly if it is selected
                e.DrawFocusRectangle();
                e.Graphics.FillRectangle(new SolidBrush(Color.Pink), rc);

                e.Graphics.DrawString(str, new Font("Ariel", 9), new SolidBrush(Color.Black), rc, sf);
            }
        }

Problem It show only data from Combobox bu nto from search_B_Click action