Change second dropdown item on selection of first dropdown item [duplicate]

Question

This question already has answers here:

How to get end date (3 answers)

Closed 9 years ago.

I have two Drop down list.

First drop down is list of months and second is for days.

I want when I select month from first drop down, items of second dropdown change according to selection of first dropdown.

For Example- if I select January from first dropdown, second drop down list become 1 to 31. On selction of february, second drop down list become 1 to 29.

I am trying with this code but not working-

protected void Page_Load(object sender, EventArgs e)
    {
        getDays(dropdownMonth.SelectedValue);

    }

public void getDays(string selectedMonth)
    {
        int i = 0;
         dropdownDays.Items.Clear();
        switch (selectedMonth)
        {
            case "January":
                i = 31;
                break;
            case "February":
                i = 29;
                break;
            case "March":
                i = 31;
                break;
            case "April":
                i = 30;
                break;
            case "May":
                i = 31;
                break;
            case "June":
                i = 30;
                break;
            case "July":
                i = 31;
                break;
            case "August":
                i = 31;
                break;
            case "September":
                i = 30;
                break;
            case "October":
                i = 31;
                break;
            case "November":
                i = 30;
                break;
            case "December":
                i = 31;
                break;
        }

        for (int j = 1; j <= i; j++)
        {
            dropdownDays.Items.Add(j.ToString());
        }
        int Month = DateTime.ParseExact(Convert.ToString(dropdownMonth.SelectedValue), "MMMM", CultureInfo.CurrentCulture).Month;
        int day = Convert.ToInt32(dropdownDays.SelectedValue);
        int year = DateTime.Now.Year;
        DateTime date = new DateTime(year, Month, day);
        lblEndDateValue.Text = String.Format("{0:dd MMMM}", date.AddDays(-1));

if i remove dropdownmonth.items.clear(); from my code then it works but then it adds new days list to previous list on this dropdown.

Answer 1

Use the Selected index changed event for first dropdownlist and set autopostback=true for first dropdown

   protected void dropdownMonth_SelectedIndexChanged(object sender, EventArgs e)
   {
       getDays(dropdownMonth.SelectedValue);
   }

set AutoPostBack="true" for dropdownDays also,

  protected void dropdownDays_SelectedIndexChanged(object sender, EventArgs e)
    {
        LabelDays.Text = dropdownDays.SelectedValue;
    }

Answer 2

Try this..You must bind your code inside !ispostback..Otherwise the on each postback the value get reset..

protected void Page_Load(object sender, EventArgs e)
{
  if(!IsPostback)
   {
       //getDays(dropdownMonth.SelectedValue);
   }
}

You can call your function in selectedidexchanged event of month dropdown and set Autopostback=true for the dropdown..I don't think you must call it on pageload..

 protected void dropdownMonth_SelectedIndexChanged(object sender, EventArgs e)
   {
       getDays(dropdownMonth.SelectedValue);
   }