C# - How can I keep an event from being skipped?

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C#

ADO.NET

forms

event

Hi everyone!

I have several combo-boxes that are supposed to contain information about different aspects of vehicles. Sometimes the combo-boxes may only have 1 element in them. I've been asked to set the default value of the combo-box to that element if there is only 1 in there. My question is how can I prevent an event from being skipped to set a value of a combo-box to that one element.

I have one vehicle that has 3 combo-boxes that all have 1 element in them. This code fires the 1st and the 3rd one, but skips the 2nd one. Can someone shed some light as to what I'm missing? I'm not getting any errors, it's just not filling in the engine-combobox in when there is one element in that combobox. It fills in the year and the transmissionCode ones just fine.

private void modelComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Sets year combobox to true and all others to false when
            // selected index changed event changes the existing value.
            yearComboBox.Enabled = true;
            engineCodeComboBox.Enabled = false;
            transmissionCodeComboBox.Enabled = false;
            okButton.Enabled = false;

            // Sets currently disabled comboboxes to have null values
            // and waits for further action from end-user.
            yearComboBox.Text = "";
            engineCodeComboBox.Text = "";
            transmissionCodeComboBox.Text = "";

            // Clears out items in comboboxes and waits for a new filtered
            // query with results.
            yearComboBox.Items.Clear();
            engineCodeComboBox.Items.Clear();
            transmissionCodeComboBox.Items.Clear();

            if (modelComboBox.SelectedIndex == -1)
            {
                yearComboBox.Enabled = false;
                engineCodeComboBox.Enabled = false;
                transmissionCodeComboBox.Enabled = false;
            }

            // Query to select non-repeating years (filtering on selected make and model)
            SqlCeCommand year_comm = new SqlCeCommand("SELECT DISTINCT year FROM vehicles WHERE make = @make AND model = @model ORDER BY year DESC", conn);
            
            year_comm.CommandType = CommandType.Text;
            year_comm.Parameters.AddWithValue("@make", makeComboBox.Text);
            year_comm.Parameters.AddWithValue("@model", modelComboBox.Text);
            year_comm.ExecuteNonQuery();

            try
            {
                SqlCeDataReader year_dr = year_comm.ExecuteReader();
                while (year_dr.Read())
                {
                    // Fills year combobox with results from query
                    yearComboBox.Items.Add(year_dr["year"]);
                }
                                                
                if (yearComboBox.Items.Count == 1)
                {
                    yearComboBox.SelectedIndex = 0;
                }                                
                                
                year_dr.Close();
                year_dr.Dispose();
            }
            catch (SqlCeException ex)
            {
                MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            finally
            {
                year_comm.Dispose();
            }
        }

        // Listener for yearcombobox selectedindexchanged event and loads the engine
        // combobox with engine type information
        private void yearComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Sets engine and transmission boxes to true.  OK button remains false until all 5 boxes have non null values.
            engineCodeComboBox.Enabled = true;
            transmissionCodeComboBox.Enabled = true;
            okButton.Enabled = false;

            // Should the selected index value change, these 2 boxes would
            // be reset to null values and wait for further selections.
            engineCodeComboBox.Text = "";
            transmissionCodeComboBox.Text = "";

            // Clears / Resets items in boxes and waits for new selections.
            engineCodeComboBox.Items.Clear();
            transmissionCodeComboBox.Items.Clear();

            if (yearComboBox.SelectedIndex == -1)
            {
                engineCodeComboBox.Enabled = false;
                transmissionCodeComboBox.Enabled = false;
            }

            SqlCeCommand engine_comm = new SqlCeCommand("SELECT DISTINCT engine_code FROM vehicles WHERE make = @make AND model = @model AND year = @year", conn);

            engine_comm.CommandType = CommandType.Text;
            engine_comm.Parameters.AddWithValue("@make", makeComboBox.Text);
            engine_comm.Parameters.AddWithValue("@model", modelComboBox.Text);
            engine_comm.Parameters.AddWithValue("@year", yearComboBox.Text);
            engine_comm.ExecuteNonQuery();

            try
            {
                SqlCeDataReader engine_dr = engine_comm.ExecuteReader();
                while (engine_dr.Read())
                {
                    engineCodeComboBox.Items.Add(engine_dr["engine_code"]);                    
                }

                if (engineCodeComboBox.Items.Count == 1)
                {
                    engineCodeComboBox.SelectedIndex = 0;
                }
 
                engine_dr.Close();
                engine_dr.Dispose();
            }
            catch (SqlCeException ex)
            {
                MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            finally
            {
                engine_comm.Dispose();
            }
        }

        // Listener for enginecombobox selectedindexchanged event and loads the transmission
        // combobox with transmission type information
        private void engineCodeComboBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            transmissionCodeComboBox.Enabled = true;
            okButton.Enabled = false;
            engineCodeComboBox.Text = "";
            transmissionCodeComboBox.Text = "";
            transmissionCodeComboBox.Items.Clear();

            // Query to select transmission type (based on previously selected make, model and year)
            SqlCeCommand trans_comm = new SqlCeCommand("SELECT DISTINCT transmission_code FROM vehicles WHERE make = @make AND model = @model AND year = @year AND engine_code = @engine_code", conn);

            trans_comm.CommandType = CommandType.Text;
            trans_comm.Parameters.AddWithValue("@make", makeComboBox.SelectedItem);
            trans_comm.Parameters.AddWithValue("@model", modelComboBox.SelectedItem);
            trans_comm.Parameters.AddWithValue("@year", yearComboBox.SelectedItem);
            trans_comm.Parameters.AddWithValue("@engine_code", engineCodeComboBox.SelectedItem);
            trans_comm.ExecuteNonQuery();

            try
            {
                SqlCeDataReader trans_dr = trans_comm.ExecuteReader();
                while (trans_dr.Read())
                {
                    // Fills trans combobox with results from query
                    transmissionCodeComboBox.Items.Add(trans_dr["transmission_code"]);
                }

                if (transmissionCodeComboBox.Items.Count == 1)
                {
                    transmissionCodeComboBox.SelectedIndex = 0;
                }      

                trans_dr.Close();
                trans_dr.Dispose();
            }
            catch (SqlCeException ex)
            {
                MessageBox.Show(ex.Message, Application.ProductName, MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
            finally
            {
                trans_comm.Dispose();
            }
        }