Easiest way to populate a drop-down list control with SharePoint custom list column values

There are numerous ways to populate a drop-down list control with SharePoint custom list column values. But for me the below seems to be the easiest one.

You should populate the drop-down list on a page load event as given in below code. You can copy the exact below code with few changes as what column values you want to populate and your drop-down list control ID/Name.

I have used here SPQuery since I want to order the column values alphabetically, starting from ascending to descending. You can omit the SPQuery statement and directly specify the column value in spList.GetItems() method.

Example: SPListItemCollection spListColl = spList.GetItems("Title"); // Title is the column name. You can mention any column name of your choice.

protected void Page_Load(object sender, EventArgs e)
{
   if (!IsPostBack)
   {
      Guid spSiteGUID = SPContext.Current.Site.ID;
      Guid spWebGUID = SPContext.Current.Site.RootWeb.ID;

      //Use above statement if your site is at root site or else below one.  

      //Guid spWebGUID = SPContext.Current.Site.OpenWeb().ID; 

      SPSecurity.RunWithElevatedPrivileges(delegate()
      {
         using (SPSite elevatedSiteColl = new SPSite(spSiteGUID))
         {
            using (SPWeb elevatedWeb = elevatedSiteColl.OpenWeb(spWebGUID))
            {
               SPList spList = elevatedWeb.Lists["QD Offices"];
               SPQuery spQuery = new SPQuery();
               spQuery.Query = "<OrderBy><FieldRef Name='Country'/></OrderBy>";
               SPListItemCollection spListColl = spList.GetItems(spQuery);

               foreach (SPListItem spItem in spListColl)
               {
                  string listItem = spItem["Title"].ToString();
                  ddl_location.Items.Add(listItem);
               }
            }
         }
      });
   }

}

Cheers !!