How to redirect aspx page from class file using timer

Question

0.00/5 (No votes)

See more:

in vb class file After every 30s i checked in database . if i get value from database then only i redirect page.
but issue at redirecting page , when i trying to redirect, i got error as 'Object Reference Not set to an instance of an object'
Please help me with this query.
Thank u in advance

What I have tried:

Public Sub Start_Timer()
Dim tym As New System.Timers.Timer
tym.Interval = 20000
tym.Start()
AddHandler tym.Elapsed, New ElapsedEventHandler(AddressOf tick)
End Sub
Public Sub tick(ByVal sender As Object, ByVal e As System.Timers.ElapsedEventArgs)
Try
Dim Conn As SqlClient.SqlConnection = New SqlClient.SqlConnection("Data Source=.\SQLEXPRESS;Initial Catalog=VMS_DB;Integrated Security=true")
Dim tab As DataTable = New DataTable
Dim query As String
Conn.Open()
query = "select Top 1 * from Vehicle_Record where Flag=1 order by Flag asc"
Dim sda As SqlClient.SqlDataAdapter = New SqlClient.SqlDataAdapter(query, Conn)
sda.Fill(tab)
If tab.Rows.Count <> 0 Then
Dim vehicle_No As String = tab.Rows(0).Item("Vehicle_No")
Dim str As String = "Vehicle_Acceptance_Form.aspx?VehicleNo=" + vehicle_No + ""
System.Web.HttpContext.Current.Response.Redirect("Vehicle_Acceptance_Form.aspx?VehicleNo=" + vehicle_No)
Dim update_Query As String = "Update Vehicle_Record set Flag=0 where Vehicle_No='" & vehicle_No & "' and Flag=1"
Dim da As SqlClient.SqlCommand = New SqlClient.SqlCommand(update_Query, Conn)
da.ExecuteNonQuery()
Conn.Close()
Else
Conn.Close()
End If
Catch ex As Exception

End Try

End Sub

Posted 5-May-16 2:01am

Tejaswi Deshmukh

Updated 5-May-16 6:24am

Add a Solution

Comments

F-ES Sitecore 5-May-16 8:11am

Which line does the error occur on?

http://stackoverflow.com/questions/4660142/what-is-a-nullreferenceexception-and-how-do-i-fix-it

Tejaswi Deshmukh 5-May-16 8:16am

System.Web.HttpContext.Current.Response.Redirect("Vehicle_Acceptance_Form.aspx?VehicleNo=" + vehicle_No) on this line error occur

F-ES Sitecore 5-May-16 10:01am

You need to learn to debug your code. Put a breakpoint on that line and see what you're referencing (ie have a "." after) that is null. Is System null? System.Web? System.WebHttoContent.Current? etc, go down the chain and see exactly what you are referencing that is null.

1 solution

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

ZurdoDev · Answer 1 · 2016-05-05T06:24:00

You cannot do it like this. The timer class cannot be used in ASP.Net like this. Why? Because the web does not work that way. You VB code sits doing nothing on the server until someone types in your url into their browser. Then the server takes the request, executes the code in the page, and then sends a response back to the client and then disconnects. So, if you kicked off a timer during that process when the timer fires there is no connection which is why .Current is null, you aren't in a current page request. It's long gone.

This is a huge difference between windows apps and web apps. If you want to redirect after some time you'll need to do it from the client side. For example, you can kick off a timer in JavaScript using setTimeout() that then checks for a response and does something depending on what you want.

You need to rethink what it is you are trying to accomplish.