asp.net vb codebehind try ... catch issue - asp.net

Question

In codebehind I have the following:
Protected Sub btnSubmit_Click(ByVal sender As Object, ByVal e As EventArgs) Handles btnSubmit.Click
Dim sql As String
Dim conn As OleDbConnection
Dim cmd As OleDbDataAdapter
Dim ds As DataSet
Dim tbl As DataTable
conn = New OleDbConnection("Provider=SQLOLEDB;Data Source=(local);Initial Catalog='library';Integrated Security=SSPI;")
Try
sql = "SELECT f1, f2, f3 FROM mydb WHERE ltrim(rtrim(UPPER(username))) = 'MYNAME'"
cmd = New OleDbDataAdapter(sql, conn)
ds = New DataSet
cmd.Fill(ds)
tbl = New DataTable
tbl = ds.Tables(0)
If tbl.Rows.Count = 0 Then
Response.Redirect("goback.html")
End If
Response.Redirect("dummy.html")
Catch ex As Exception
Response.Redirect("goback2.html")
End Try
End Sub
The routine works to a point. I can check the value of tbl.Rows.Count = 1, so it should redirect to "dummy.html" WHICH IT DOES CORRECTLY so long as I comment out the line that redirects to "goback2.html".
If I uncomment the line to redirect to goback2, then it goes to "goback2.html"
I thought it should only execute that code if there was some error in the previous code - but there can't be an error in the previous code, if it executes. It's like it's executing the catch code regardless of what I'm going.
Oddly, it ONLY messes up with the redirect! If I replace the redirect to goback2 with an assignment to a textbox.text then it works (by ignoring that code) - but the redirect it seems to execute regardless of whether it should take the catch

Answer 1

Response.Redirect(string) throws a ThreadAbortException when Response.End() is called.
Use the overload that takes a string and a boolean instead:
Response.Redirect("goback.html", false);
From MSDN: the second parameter, endResponse, "Indicates whether execution of the current page should terminate."

Answer 2

Response.Redirect throws a ThreadAbortException to terminate the current request.
Your Catch block is catching that exception.

Answer 3

It may be because of ThreadAbortedException because of Response.Redirect. - MSDN support link

Answer 4

You haven't open the connection. You cannot redirect in an Try/Catch. You should set a boolean variable success to false and check for it after the Try/Catch/Finally and redirect if it's set to false.
Have a look at this SO-Question: Is there something that prevents Response.Redirect to work inside try-catch block?
This would be better:
Dim success As Boolean = True
Dim ds As New DataSet
Using conn As New OleDb.OleDbConnection("Provider=SQLOLEDB;Data Source=(local);Initial Catalog='library';Integrated Security=SSPI;")
Try
Dim Sql = "SELECT f1, f2, f3 FROM mydb WHERE ltrim(rtrim(UPPER(username))) = 'MYNAME'"
Dim cmd = New OleDb.OleDbDataAdapter(Sql, conn)
conn.Open()
cmd.Fill(ds)
Catch ex As Exception
success = False
End Try
End Using
If Not success Then
Response.Redirect("goback2.html")
ElseIf ds.Tables.Count <> 0 AndAlso ds.Tables(0).Rows.Count = 0 Then
Response.Redirect("goback.html")
Else
Response.Redirect("dummy.html")
End If