How to sort DropDownList items in descending order in asp.net

DropDownList items sort order by descending

DropDownList is an asp.net list web server control that allow us to select one item at a time from a drop-down-list. by default dropdownlist items are not sorted. to provide better user experience, web developer wants to create a sorted dropdownlist. the following asp.net c# example code demonstrate us how can we render a dropdownlist server control which items are descending sorted.

DropDownList server control have no built in property or method to sort its items descending or ascending order. we need to apply few techniques to display a sorted dropdownlist programmatically.

At first we create a generic list which data type is ListItem. now we populate the generic list from dropdownlist items collection. next we sort the list by descending order using Linq OrderByDescending() extension method. finally we clear the dropdownlist items, and repopulate the dropdownlist with the sorted generic list. now we can display a descending sorted dropdownlist on web browser. sorting applied for first page load time only, because we track the postback using page IsPostBack property.

dropdownlist-sort-order-by-descending.aspx


<%@ Page Language="C#" AutoEventWireup="true"%>    
      
<!DOCTYPE html>
        
<script runat="server">  
    protected void Page_Load(object sender, EventArgs e)  
    {   
        if(!Page.IsPostBack)
        {
            //create a generic list data type ListItem
            List<ListItem> list = new List<ListItem>();

            foreach (ListItem litem in DropDownList1.Items)
            {
                //add ListItem to generic list
                list.Add(litem);
            }

            //sort list items by item text descending
            List<ListItem> sorted = list.OrderByDescending(b => b.Text).ToList();

            //clear dropdownlist items
            DropDownList1.Items.Clear();

            //repopulate dropdownlist with sorted items.
            foreach (ListItem litem in sorted)
            {
                DropDownList1.Items.Add(litem);
            }
        }
    }
</script>        
        
<html xmlns="http://www.w3.org/1999/xhtml">        
<head id="Head1" runat="server">        
    <title>asp.net c# dropdownlist sort order by descending</title>  
</head>        
<body>        
    <form id="form1" runat="server">        
    <div>        
        <h2 style="color:MidnightBlue; font-style:italic;">        
            asp.net c# example - dropdownlist sort order by descending
        </h2>        
        <hr width="550" align="left" color="Gainsboro" />        
        <br /><br />  
        <asp:DropDownList  
            ID="DropDownList1"  
            runat="server"  
            AutoPostBack="true"  
            Width="350"  
            Font-Size="X-Large"  
            Font-Names="Comic Sans MS"
            >  
            <asp:ListItem Text="Grey Goshawk" Value="1"></asp:ListItem>
            <asp:ListItem Text="African Harrier Hawk" Value="2"></asp:ListItem>
            <asp:ListItem Text="Northern Goshawk" Value="3"></asp:ListItem>
            <asp:ListItem Text="Common Black Hawk" Value="4"></asp:ListItem>
            <asp:ListItem Text="Philippine Eagle" Value="5"></asp:ListItem>
        </asp:DropDownList>  
    </div>        
    </form>        
</body>        
</html>

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