Non-Databound DropDownList SelectedValue Problem

When you have an asp:DropDownList which is *not* databound, (i.e. you add the items manually) there are a few things you have to do to get 'SelectedValue' to work. ASP.NET will ignore the 'SelectedValue' when you manually add items unless you make a call to 'DataBind' on the drop down list, so you need to add this line of code to force ASP.NET to select the correct item. However, because the 'DropDownList.Items.Add()' function will accept a string, its all too tempting to pass in the string you want to display when adding the items, but this will cause an error when you try to databind! e.g.

ddlYear.Items.Clear()
For yr As Integer = Now.Date.Year - 100 To Now.Date.Year - 18
   ddlYear.Items.Add(yr.ToString())
Next

ddlYear.DataBind() '<-- This part tries to load SelectedValue - but will error!

Error: 'DropDownList' has a SelectedValue which is invalid because it does not exist in the list of items. What you need to do, is pass in 'new ListItem()' to the Items.Add() function and specify that the string is the 'text' and 'value' for the list item. e.g.

ddlYear.Items.Clear()
For yr As Integer = Now.Date.Year - 100 To Now.Date.Year - 18
  ddlYear.Items.Add(New ListItem(yr.ToString(), yr.ToString()))
Next

ddlYear.DataBind()

You should find that the drop down list will now load with your manually added items and will display the correct 'SelectedValue'!