C# combobox 上的 SelectedIndexChanged 方法存在問題

Question

我正在學習 C# 並且正在制作自定義工資單應用程序。 我有一個雇主期間的表格，允許用戶一次輸入/編輯或刪除一個工資單期間，即在給定時間數據庫中只能有一條記錄。

我有一個表單加載方法，如果存在工資單期，它將檢索所有需要的字段。

代碼：

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_month.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;
    }
}

到目前為止，我的 2 個組合框有兩個選定的索引更改事件：

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();
}

我的問題：在我使用任何SelectedIndexChanged方法之前，數據庫中的所有值都顯示在它們相應的文本框和組合框中。

但是，在添加cb_number_hours_SelectedIndexChanged方法后，在cb_number_hours.Text停止顯示后，數據庫中的所有文本框和 combobox 值。 這導致方法中的計算不起作用，因為(int.Parse(cb_number_days_week.Text))被視為 null。

我該如何解決？

Answer 1

在您的cb_number_hours_SelectedIndexChanged事件處理程序中，嘗試在代碼的 rest 之前添加一個有效值檢查，如下所示（未經測試）：

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();
}