how to disable default selection in dropdownlist in asp.net

i want the code to disable开发者_开发百科 default selection in dropdownlist in asp.net and also on selection of a particular data field the values are displayed in the txtbox below.the dropdown should be filled with system related data like eg c:drive, d ... etc dynamically at run time.

then you can manually append ""--select--"" in the first place in the dropdownlist by edit items. and set appenddatabounditems to true.. thus you will get select in the first place rather than the first drive by default...... ok then use this function and cal this function on the databound event of dropdownlist.

void RemoveDuplicateItems(DropDownList ddl)
    {
        for (int i = 0; i < ddl.Items.Count; i++)
        {
            ddl.SelectedIndex = i;
            string str = ddl.SelectedItem.ToString();
            for (int counter = i + 1; counter < ddl.Items.Count; counter++)
            {
                ddl.SelectedIndex = counter;
                string compareStr = ddl.SelectedItem.ToString();
                if (str == compareStr)
                {
                    ddl.Items.RemoveAt(counter);
                   counter = counter - 1;
                }
            }
        }
    }

and call this function in dropdownlist_databound() event.

then you can manually append ""--select--"" in the first place in the dropdownlist by edit items. and set appenddatabounditems to true.. thus you will get select in the first place rather than the first drive by default......