Can't change properties of a databoud dropdownlist in a user contr

[ASP Developer]

I have a databound dropdownlist in a user control (ascx file). In the
corresponding aspx page I would like to be able to change the selectedindex
of the dropdownlist. So I set up a property in the ascx file to do so.
However, I keep getting the error: object is not set to an instance of an
object. I think this is a timing error because if I hard code the values it
runs fine. Any help would be greatly appreciated.

*********************Aspx page **************
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load

Dim tempUserControl = Page.LoadControl("populatedropdown.ascx")
tempUserControl.myProp = "Test"
end sub
'*******************Ascx page*************

Public Property myProp() As String
Get
Return dropdownlist1.SelectedIndex
End Get
Set(ByVal Value As String)
DropDownList1.Items.FindByValue(Value).Selected = True
End Set
End Property
Private Sub Page_Load(ByVal sender As System.Object, ByVal e As
System.EventArgs) Handles MyBase.Load
'Put user code to initialize the page here

Call populatedropdown()
End Sub

Function populatedropdown()
Dim vArray As DataTable
Dim dt As New DataTable()
Dim dr As DataRow
Dim ozaweb As New plnwrapper.wrapper()
dt = ozaweb.GetVillageTypes

DropDownList1.DataSource = dt
DropDownList1.DataTextField = dt.Columns(1).ColumnName
DropDownList1.DataValueField = dt.Columns(0).ColumnName
DropDownList1.DataBind()

End Function