Problem getting selected value from DropDownList using ArrayList as DataSource

[kwilliams]

I'm having a problem getting the selected value from a DropDownList that uses an ArrayList as a DataSource. When I select a year and click on the submit button, I get the following error message:

Object reference not set to an instance of an object.

Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.

I'm not understanding why this isn't working. The years (1900 - 1993) are getting populated into the DropDownList without a problem, but on the btnSubmit_Click job gets submitted, I get that error. And and all help would be appreciated. Hopefully it's something simple that I'm missing.

Here's the code I'm using:

VB.NET CODE-BEHIND:
'Assign date variables
Dim dtCurrDate As DateTime = DateTime.Now 'Assign current date
Dim intCurrYear As Integer = DateTime.Now.Year 'Assign current year
Dim intVotingYear As Integer = intCurrYear - 18 'Assign voting year

Sub Page_Load(ByVal Sender As Object, ByVal E As EventArgs) Handles Me.Load

If Not Page.IsPostBack Then 'loads with page

'Declare an array for the dynamic dropdownlist
Dim colArrayList As New System.Collections.ArrayList()

'Declare loop variables
Dim i As Integer = 1900
Dim intDisplayYear As Integer = i

'Loop through years
For i = 1900 To intVotingYear
colArrayList.Add(i)
colArrayList.TrimToSize()
colArrayList.Sort() 'Sort years
colArrayList.Reverse() 'Reverse sort/descending order
Next

'Bind data
ddlYear.DataSource = colArrayList
ddlYear.DataBind()

'Add a new listitem to the beginning of the dropdownlist
ddlYear.Items.Insert(0, New ListItem("- Year -", "")) 'Text, value
ddlYear.SelectedIndex = ddlYear.Items.IndexOf(ddlYear.Items.FindByText(Session("SelectedYear")))

End If

End Sub

Sub btnSubmit_Click(ByVal Sender As Object, ByVal E As EventArgs)

'Declare form variables
Dim strFormYear As String = ddlYear.SelectedItem.Text '<<<<-----THIS IS WHERE I GET THE ERROR

'NOTE: I've also tried changing the above line to:
'Dim strFormYear As String = ddlYear.SelectedItem.Value
'...but that resulted in the same error.

'Declare session variables
Session("SelectedYear") = dob_year_form

If Page.IsValid Then
Try...
...
End If

End Sub

ASP.NET PAGE:
<form id="form1" method="post" runat="server">

<asp:DropDownList id="ddlYear" runat="server"></asp:DropDownList>

<asp:Button ID="btnSubmit" Text="Submit" OnClick="btnSubmit_Click" runat="server" />

</form>

[kwilliams]

I thought that posting my solution might help others, so here it goes:

After getting some advice from another forum user, I was able to solve the problem by taking a step back. I did that by using a simple example of the ArrayList at W3Schools at http://www.w3schools.com/aspnet/aspnet_arraylist.asp to compare it to my code. The issue ended up being in the page declaration. I had EnableViewState="false", and I changed it to EnableViewState="true". Once I did that, and I placed the initial code within an "If Not Page.IsPostBack Then...", it worked as it should.