Hi

I have a funtion within a class in my App_Code folder that returns a SQLDataReader.

When I reference this function from within my CodeBehind to populate a DataList, I get the Object reference not set to an instance of an object error. However, if I put the function inside my code behind it works fine.

Here is the class and function:

1    Imports Microsoft.VisualBasic
2    Imports System
3    Imports System.Data
4    Imports System.Data.Sql
5    Imports System.Data.SqlClient
6    
7    
8    Namespace ULT
9    
10       Public Class CMSTools
11   
12           Public objConn As SqlConnection = New SqlConnection(ConfigurationManager.ConnectionStrings("SQL2005_317692_simoneConnectionString").ConnectionString)
13   
14           Function GetSegmentsByParentID(ByVal parentID) As SqlDataReader
15   
16               Dim objCmd As SqlCommand
17   
18               objCmd = New SqlCommand("cms_GetSegmentsByParentID", objConn)
19               objCmd.CommandType = CommandType.StoredProcedure
20   
21               objCmd.Parameters.Add(New SqlParameter("@parentID", SqlDbType.Int))
22               objCmd.Parameters("@parentID").Value = parentID
23   
24               Try
25                   objConn.Open()
26                   Return objCmd.ExecuteReader(CommandBehavior.CloseConnection)
27               Catch ex As SqlException
28                   Throw ex
29               End Try
30   
31           End Function
32   
33       End Class
34   
35   End Namespace
36   

Here is my Code Behind:

1    Imports System
2    Imports System.Data
3    Imports System.Data.Sql
4    Imports System.Data.SqlClient
5    
6    
7    Partial Class admin_CMS_Editor
8        Inherits System.Web.UI.Page
9    
10       Public objCMSTools As ULT.CMSTools
11   
12       Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
13           Dim parentID As Integer
14           parentID = 1
15   
16           'get the list of current segments for this page
17   
18           ListCurrentSegments(parentID)
19   
20       End Sub
21   
22   
23       Sub ListCurrentSegments(ByVal parentID)
24   
25           Dim objReader As SqlDataReader = objCMSTools.GetSegmentsByParentID(parentID)
26   
27           DataList1.DataSource = objReader
28           DataList1.DataBind()
29          
30   
31       End Sub

If I copy the funtion GetSegmentsByParentID from the class file into my CodeBehind and reference it like so 

Dim objReader As SqlDataReader = GetSegmentsByParentID(parentID)

it seems to work fine. Any ideas why it is returning this error when I try to use it from within my class?

 Thanks 

Hi Shauns1,

You are getting this error message as you are trying to access a method directly from your page without create new instance of the class in which the definition of  method exists.

You will need to use something like this in your code behind file

Public objCMSTools As NEW ULT.CMSTools

          Dim objReader As SqlDataReader = objCMSTools.GetSegmentsByParentID(parentID)
          DataList1.DataSource = objReader
          DataList1.DataBind()

Hope this helps

Hi,

 You can get this explanation well here

Object Reference Not Set to an instance of a object

Hi,

I get the same error when I try to do the following:

1    Dim conn As New SqlClient.SqlConnection
2            conn.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\WebSites\Tavlikos\App_Data\Database.mdf;Integrated Security=True;User Instance=True"
3            Dim comm As New SqlCommand("SELECT ImageFileName FROM Projects WHERE Description=@Description", conn)
4            comm.Parameters.Add("@Description", SqlDbType.NVarChar, 50).Value = "μονοκατοικία στον Σταυρό Θεσσαλονίκης"
5    
6            Dim da As SqlDataAdapter = New SqlDataAdapter(comm)
7            Dim ds As DataSet = New DataSet
8            Dim count As Integer
9            conn.Open()
10           count = da.Fill(ds, "Projects")
11           conn.Close()
12           Dim i As Integer = 0
13   
14           Dim dr As DataRow
15           For Each dr In ds.Tables("Projects").Rows
16               imgButtons(i).ImageUrl = Me.ResolveUrl("images/" + dr.Item("ImageFileName").ToString)
17               i = i + 1
18           Next
19       End Sub

 To explain this,I have the image filename to the sql database,which I retrieve with the above query....The real images are in the folder "images",so I combine in line 16 the url of the image...

Any idea would be helpful...

Thanks!

i would suspect this:

imgButtons(i).ImageUrl

do you actually have an array of ImageButtons?
and if so, does it have enough entries?

Yes,I have already created an array of ImageButtons as following:

1     Public Sub SetImageButtons()
2            imgButtons(0) = ImageButton1
3            imgButtons(1) = ImageButton2
4            imgButtons(2) = ImageButton3
5            imgButtons(3) = ImageButton4
6            imgButtons(4) = ImageButton5
7            imgButtons(5) = ImageButton6
8            imgButtons(6) = ImageButton7
9        End Sub

But,wait a minute......I just realised that I called the function nowhere in the code as far as I can see....

..Ok,everything works fine now...here is the code(quite simple at last):

1    Public Sub SetImageButtons()
2            imgButtons(0) = ImageButton1
3            imgButtons(1) = ImageButton2
4            imgButtons(2) = ImageButton3
5            imgButtons(3) = ImageButton4
6            imgButtons(4) = ImageButton5
7            imgButtons(5) = ImageButton6
8            imgButtons(6) = ImageButton7
9        End Sub
10   
11       Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
12           SetImageButtons()
13           Dim conn As New SqlClient.SqlConnection
14           conn.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\WebSites\Tavlikos\App_Data\Database.mdf;Integrated Security=True;User Instance=True"
15           Dim comm As New SqlCommand("SELECT ImageFileName FROM Projects WHERE Description=@Description", conn)
16           comm.Parameters.Add("@Description", SqlDbType.NVarChar, 50).Value = "μονοκατοικία στον Σταυρό Θεσσαλονίκης"
17   
18           Dim da As SqlDataAdapter = New SqlDataAdapter(comm)
19           Dim ds As DataSet = New DataSet
20           Dim count As Integer
21           conn.Open()
22           count = da.Fill(ds, "Projects")
23           conn.Close()
24           Dim i As Integer = 0
25   
26           Dim dr As DataRow
27           For Each dr In ds.Tables("Projects").Rows
28               imgButtons(i).ImageUrl = "images/" + dr.Item("ImageFileName")
29               i = i + 1
30           Next
31       End Sub

Thanks for the help!!!

Problems that can occur with this sort of given a specific array size before assigning their respectuve value(s) to the button , what of if the records returned is more or less than what expected, what will happen to the system. From my perceptive, I thing the best is to get the total record count and pass that to teh method to create the button list and later use that to populate the button value that is

public  SUb SetImageButtons(cnt)

for i as Integer=0 to cnt - 1

imgButtons(i) = ImageButton & (i+1)

end Sub

Dim numOfCount as Integer = 0

Dim conn As New SqlClient.SqlConnection
14           conn.ConnectionString = "Data Source=.\SQLEXPRESS;AttachDbFilename=C:\WebSites\Tavlikos\App_Data\Database.mdf;Integrated Security=True;User Instance=True"
15           Dim comm As New SqlCommand("SELECT count(ImageFileName) FROM Projects WHERE Description=@Description", conn)
16           comm.Parameters.Add("@Description", SqlDbType.NVarChar, 50).Value = "μονοκατοικία στον Σταυρό Θεσσαλονίκης"
17  
18           numOfCount = comm.ExecuteScalar()

SetImageButtons(numOfCount)

and consequent statement follows.

thanks