"Object variable or With block variable not set." issue

[adascat]

Got title problem for the codes below, can anyone help to have a look what's wrong here? Thanks a million. - A newbie

Description:
An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.

Exception Details:
System.NullReferenceException: Object variable or With block variable not set.

Source Error:
Line 24: ResultsGrid.DataSource = aDataSet.Tables("Translator Awaiting Approval")

 
Imports System.Data
Imports System.Data.OleDb
 
Partial Class _Default
    Inherits System.Web.UI.Page
 
    Private ResultsGrid As Object
 
 
    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        If Not IsPostBack Then
            Dim aConnection = New OleDbConnection
            Dim aConnectionString As String
            Dim SQLQuery As String
            Dim aDataAdapter = New OleDbDataAdapter
            Dim aDataSet = New DataSet
            aConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source =" & _
                Server.MapPath("/App_Data/abc.accdb")
            aConnection.ConnectionString = aConnectionString
            SQLQuery = "Select TranslatorEmail From Translator Where IsTranslatorRegistered = False"
            aDataAdapter.SelectCommand = New OleDbCommand(SQLQuery, aConnection)
            aDataAdapter.SelectCommand.Connection.Open()
            aDataAdapter.Fill(aDataSet, "Translator Awaiting Approval")
            ResultsGrid.DataSource = aDataSet.Tables("Translator Awaiting Approval")
            Page.DataBind()
 
        End If
    End Sub
 
End Class

[Frinavale]

Whenever you retrieve anything from an external source (like a database in your case) you should check to make sure that you have actually retrieved the data.

It sounds like your retrieval of data failed in some way.

Or you don't have a table named "Translator Awaiting Approval" in your DataSet.

Either way, you will get a System.NullReferenceException when you attempt to use an object that hasn't been initialized. You will see it when you try to call a method or use a Property on "Nothing" or "Null".

-Frinny

[adascat]

Thank you Frinny.

In a different page, I met another problem while attempting to retrieve data from the accdb file, error msg is listed below and I guess it's the data file connection problem?

Exception Details: System.Data.OleDb.OleDbException: Unrecognized database format 'C:\Users\Lili\Documents\Visual Studio 2010\Projects\WebApplication1\WebApplication1\App_ Data\CS5012ProjectAY201011.accdb'.

Stack Trace:

[OleDbException (0x80004005): Unrecognized database format 'C:\Users\Lili\Documents\Visual Studio 2010\Projects\WebApplication1\WebApplication1\App_Data\CS5012ProjectAY201011.accdb'.]
   System.Data.OleDb.OleDbConnectionInternal..ctor(OleDbConnectionString constr, OleDbConnection connection) +337
   System.Data.OleDb.OleDbConnectionFactory.CreateConnection(DbConnectionOptions options, Object poolGroupProviderInfo, DbConnectionPool pool, DbConnection owningObject) +86
   System.Data.ProviderBase.DbConnectionFactory.CreateNonPooledConnection(DbConnection owningConnection, DbConnectionPoolGroup poolGroup) +31
   System.Data.ProviderBase.DbConnectionFactory.GetConnection(DbConnection owningConnection) +76
   System.Data.ProviderBase.DbConnectionClosed.OpenConnection(DbConnection outerConnection, DbConnectionFactory connectionFactory) +126
   System.Data.OleDb.OleDbConnection.Open() +43
   WebApplication1.WebForm2.Button1_Click(Object sender, EventArgs e) in C:\Users\Lili\Documents\Visual Studio 2010\Projects\WebApplication1\WebApplication1\Registration.aspx.vb:30
   System.Web.UI.WebControls.Button.OnClick(EventArgs e) +118
   System.Web.UI.WebControls.Button.RaisePostBackEvent(String eventArgument) +112
   System.Web.UI.WebControls.Button.System.Web.UI.IPostBackEventHandler.RaisePostBackEvent(String eventArgument) +10
   System.Web.UI.Page.RaisePostBackEvent(IPostBackEventHandler sourceControl, String eventArgument) +13
   System.Web.UI.Page.RaisePostBackEvent(NameValueCollection postData) +36
   System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint, Boolean includeStagesAfterAsyncPoint) +5563
 
Version Information: Microsoft .NET Framework Version:4.0.30319; ASP.NET Version:4.0.30319.1
 

It feels like getting messy now :(

[adascat]

I think I got the above issues(db format unrecognized) solved by changed the provider version to 12 instead of 4 and changed the provider info in the web.config. :)

And the "Object variable or With block variable not set." issue now becomes "Object reference not set to an instance of an object"! This page is working well seperately, however when I generate the view for main default page, it anyhow points to page of below codes, claiming that:

System.NullReferneceException: Object reference not set to an instance of an object.

Problematic line:
Gridview1.DataSource = aDataSet.Tables("Results")

# Imports System.Data
# Imports System.Data.OleDb
#  
# Partial Class _Default
#     Inherits System.Web.UI.Page
#  
#  
#     Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
#         If Not IsPostBack Then
#             Dim aConnection = New OleDbConnection
#             Dim aConnectionString As String
#             Dim SQLQuery As String
#             Dim aDataAdapter = New OleDbDataAdapter
#             Dim aDataSet = New DataSet
#             aConnectionString = "Provider=Microsoft.ACE.OLEDB.12.0;Data Source =" & _
#                 Server.MapPath("/App_Data/abc.accdb")
#             aConnection.ConnectionString = aConnectionString
#             SQLQuery = "Select TranslatorEmail From Translator Where IsTranslatorRegistered = False"
#             aDataAdapter.SelectCommand = New OleDbCommand(SQLQuery, aConnection)
#             aDataAdapter.SelectCommand.Connection.Open()
#             aDataAdapter.Fill(aDataSet, "Translator Awaiting Approval")
#             Gridview1.DataSource = aDataSet.Tables("Translator Awaiting Approval")
#             Gridview1.DataBind()
#  
#         End If
#     End Sub
#  
# End Class
 

Any clue on why this is happening?