VB.NET DataSet table data empty - vb.net

Question

I'm trying to use the dataset for a report, but the data is gone when I try to use it. Here is my code for the most part:
Variables:
Dim ResultsDataView As DataView
Dim ResultsDataSet As New DataSet
Dim ResultsTable As New DataTable
Dim SQLQuery As String
Search:
This is where a datagrid is populated in the main view. The data shows up perfectly.
Private Sub Search(Optional ByVal Bind As Boolean = True, Optional ByVal SearchType As String = "", Optional ByVal SearchButton As String = "")
Dim SQLQuery As String
Dim ResultsDataSet
Dim LabelText As String
Dim MultiBudgetCenter As Integer = 0
SQLQuery = "A long and detailed SQL query that grabs N rows with 7 columns"
ResultsDataSet = RunQuery(SQLQuery)
ResultsTable = ResultsDataSet.Tables(0)
For Each row As DataRow In ResultsTable.Rows
For Each item In row.ItemArray
sb.Append(item.ToString + ","c)
Response.Write(item.ToString + "\n")
Response.Write(vbNewLine)
Next
sb.Append(vbCr & vbLf)
Next
'Response.End()
If Bind Then
BindData(ResultsDataSet)
End If
End Sub
Binding Data:
I think this is a cause in the issue.
Private Sub BindData(ByVal InputDataSet As DataSet)
ResultsDataView = InputDataSet.Tables("Results").DefaultView
ResultsDataView.Sort = ViewState("SortExpression").ToString()
ResultsGridView.DataSource = ResultsDataView
ResultsGridView.DataBind()
End Sub
Reporting action:
This is where I am trying to use the table data. But it is showing as nothing.
Protected Sub ReportButton_Click(sender As Object, e As EventArgs) Handles ReportButton.Click
For Each row As DataRow In ResultsTable.Rows
For Each item In row.ItemArray
Response.Write(item.ToString)
Next
Next
End Sub
The reason I'm trying to loop through this data is to both display the data in a gridview on the main view as well as export the data to CSV. If there is a different way to export a SQL query to CSV, I'm open to any suggestions.
There has to be something I can do to get the data from the SQL query to persist through the ReportButton_Click method. I've tried copying the datatable, I've tried global variables, I've tried different methods of looping through the dataset. What am I missing?!
Thank you all in advance.
EDIT
Here is the Page_Load:
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
If Page.IsPostBack Then
'set focus to postback control
Dim x As String = GetPostBackControlName(Page)
If Len(x) > 0 Then
x = x.Replace("$", "_")
SetFocus(x)
End If
End If
If Not IsPostBack Then
ResultsGridView.AllowPaging = False
'Enable Gridview sorting
ResultsGridView.AllowSorting = True
'Initialize the sorting expression
ViewState("SortExpression") = "ID DESC"
'Populate the Gridview
Search()
End If
End Sub

Answer 1

In your search function add this line after the ResultsTable setting
ResultsTable = ResultsDataSet.Tables(0)
Session("LastSearch") = ResultsTable
Then in your report click event handler recover your data from the Session variable
Protected Sub ReportButton_Click(sender As Object, e As EventArgs) Handles ReportButton.Click
ResultsTable = DirectCast(Session("LastSearch"), DataTable)
For Each row As DataRow In ResultsTable.Rows
For Each item In row.ItemArray
Response.Write(item.ToString)
Next
Next
End Sub
You need to read about ASP.NET Life Cycle and understand that every time ASP.NET calls your methods it creates a new instance of your Page class. Of course this means that global page variables in ASP.NET are not very useful.
Also consider to read about that Session object and not misuse it.
What is the difference between SessionState and ViewState?