C# problem with SelectedIndexChanged method on combobox

I am learning C# and am making a custom Payroll application. I have a form for employer periods that allows a user to enter/edit or delete one payroll period at a time, i.e, there can only be one record in the database at a given time.

I have a method on form load that will retrieve all needed fields if a payroll period exists.

Code:

private void PayrollPeriodForm_Load(object sender, EventArgs e)
{
    dateTimePicker2.Value = dateTimePicker2.Value.AddYears(1).AddDays(-1);

    // Get service instance
    var employerPeriodService = Program.Kernel.Get<IEmployerPeriodService>();

    //Query database
    var employerPeriods = employerPeriodService.GetAllEmployerPeriods();                                      

    if (employerPeriods.Any(x => x != null))
    {
        var employerPeriod = employerPeriods.First();

        txt_tax_year.Text = employerPeriod.U_Tax_year.ToString();
        lbl_code.Text = employerPeriod.Code;
        cb_number_hours.Text = employerPeriod.U_Day_hrs.ToString();
        cb_number_days_week.Text = employerPeriod.U_Week_days.ToString();
        cb_number_days_month.Text = employerPeriod.U_Month_days.ToString();
        cb_number_days_fortnight.Text = employerPeriod.U_Fortnight_days.ToString();
        txt_number_hours_week.Text = employerPeriod.U_Week_hrs.ToString();
        txt_number_hours_fortnight.Text = employerPeriod.U_Fortnight_hrs.ToString();
        txt_number_hours_month.Text = employerPeriod.U_Month_hrs.ToString();
        cb_avg_weeks_month.Text = employerPeriod.U_Weeks_in_month.ToString();
        cb_avg_fortnights_month.Text = employerPeriod.U_No_of_Fortnights.ToString();
        dateTimePicker1.Text = employerPeriod.U_Starting_period.ToString();
        dateTimePicker2.Text = employerPeriod.U_Ending_period.ToString();

        txt_tax_year.Enabled = false;
        dateTimePicker1.Enabled = false;
        dateTimePicker2.Enabled = false;
        btn_add.Enabled = false;
        btn_update.Enabled = true;
        btn_delete.Enabled = true;
        btn_update.Visible = true;
        btn_delete.Visible = true;
        btn_add.Visible = false;

        // Store SAP code
        SAPCodePeriod = employerPeriod.Code;
    }
    else
    {
        //clear textfields after input
        cb_number_hours.SelectedIndex = 0;
        cb_number_days_week.SelectedIndex = 0;
        txt_number_hours_week.Text = "";
        cb_number_days_month.SelectedIndex = 0;
        txt_number_hours_month.Text = "";
        cb_number_days_fortnight.SelectedIndex = 0;
        txt_number_hours_fortnight.Text = "";
        cb_avg_weeks_month.Text = null;
        cb_avg_fortnights_mo开发者_运维技巧nth.Text = null;
        lbl_code.Text = "";

        txt_tax_year.Enabled = true;
        dateTimePicker1.Enabled = true;
        dateTimePicker2.Enabled = true;
        btn_add.Enabled = true;
        btn_update.Enabled = false;
        btn_delete.Enabled = false;
        btn_add.Visible = true;
        btn_update.Visible = false;
        btn_delete.Visible = false;
    }
}

I have two selectd index changed events for 2 of my comboboxes so far:

private void cb_number_hours_SelectedIndexChanged(object sender, EventArgs e)
{
    // calculate hours/week
    var hoursWeek = (int.Parse(cb_number_hours.Text)) * (int.Parse(cb_number_days_week.Text));

    txt_number_hours_week.Text = hoursWeek.ToString();
}

private void cb_number_days_week_SelectedIndexChanged(object sender, EventArgs e)
{
    // calculate hours/week
    var hoursWeek = (int.Parse(cb_number_hours.Text)) * int.Parse(cb_number_days_week.Text);

    txt_number_hours_week.Text = hoursWeek.ToString();
}

My Problem: Before I had any of the SelectedIndexChanged methods, All the values from the database were showing in their appropriate textboxes and comboboxes.

However after adding the cb_number_hours_SelectedIndexChanged method, all textbox and combobox values from the DB after cb_number_hours.Text stopped showing. This has resulted in The calculation in the methods not to work as (int.Parse(cb_number_days_week.Text)) is seen as null.

How do I fix this?

In your cb_number_hours_SelectedIndexChanged event handler, try adding a check for a valid value before the rest of your code, like this (untested):

int hours;
int days;

if (Int32.TryParse(cb_number_hours.Text, out hours) && Int32.TryParse(cb_number_days_week.Text, out days))
{
   var hoursWeek = hours * days;
   txt_number_hours_week.Text = hoursWeek.ToString();
}