如何避免dropdownlist再次显示该值 [英] how to avoid dropdownlist to show the value again

问题描述

如何避免dropdownlist再次显示该值。 Plz帮我解决这个问题

how to avoid dropdownlist to show the value again. Plz help me to solve this

public enum Month
    {
        Jan = 1,
        Feb,
        Mar,
        Apr,
        May,
        Jun,
        Jul,
        Aug,
        Sep,
        Oct,
        Nov,
        Dec
    }
    protected void Page_Load(object sender, EventArgs e)
    {
        if (!Page.IsPostBack)
        {
            PopulateDate();
        }
     
    }
    
    public void PopulateDate()
    {
        ddlyear.Items.Insert(0, "-----------Select----------");
        Int32 index = 1;
        for (int year = 1950; year <= DateTime.Now.Year; year++)
        {
            ListItem Item = new ListItem(year.ToString());
            ddlyear.Items.Insert(index, Item);
            index++;
        }
        ddlMonth.Items.Insert(0, "-------Select-------");
        for(int i=1;i<=12;i++)
        {
            String str = ((Month)i).ToString();
            ListItem Item = new ListItem(str, i.ToString());
            ddlMonth.Items.Insert(i, Item);
        }

    }

   
    protected void ddlMonth_SelectedIndexChanged(object sender, EventArgs e)
    {
        String Year = ddlyear.SelectedValue;
        String Month = ddlMonth.SelectedValue;
        Int32 Days = DateTime.DaysInMonth(Convert.ToInt32(Year), Convert.ToInt32(Month));
        ddlday.Items.Insert(0, "-------------Select--------------");
        for (int i = 1; i <= Days; i++)
        {
            ListItem Item = new ListItem(i.ToString(), i.ToString());
            ddlday.Items.Insert(i, Item);
        }
        
    }

推荐答案

添加此行

< br $> b $ b

add this line

protected void ddlMonth_SelectedIndexChanged1(object sender, EventArgs e)
       {
           ddlday.Items.Clear(); 
           String Year = ddlyear.SelectedValue;
           String Month = ddlMonth.SelectedValue;

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