Dataset returning Null in VB 2008

N

Nab

This code for a webservice is returning a dataset with a Null value (by
throwing a System.NullReferenceException) when using VB2008. The GUI is used
to establish a connection and adapter to an MS Access database (with a table
named EstateAgents). I had no problem when used this code with VB2005. Here's
the code:

<WebMethod()> _
Public Function GetEstateAgents() As DataSet
Dim estateDataset As DataSet = New DataSet
estateOleAdapter.Fill(estateDataset, "EstateAgents")
Return estateDataset
estateOleConnection.Close()
End Function

Any suggestions will be gratefully received.
 
J

John Saunders

Nab said:
This code for a webservice is returning a dataset with a Null value (by
throwing a System.NullReferenceException) when using VB2008. The GUI is
used
to establish a connection and adapter to an MS Access database (with a
table
named EstateAgents). I had no problem when used this code with VB2005.
Here's
the code:

<WebMethod()> _
Public Function GetEstateAgents() As DataSet
Dim estateDataset As DataSet = New DataSet
estateOleAdapter.Fill(estateDataset, "EstateAgents")
Return estateDataset
estateOleConnection.Close()
End Function

Exactly where is the NullReferenceException occurring? Please post the
complete exception. Also, what do you mean that the GUI establishes the
connection? Is the GUI establishing the connection and the service trying to
use it? Why would that work?
 
N

Nab

I hope you could shed some light on this John. What I mean by “The GUI
establishes the connection) is that I dragged the OleDbConnection icon on the
toolbox to the design area to establish the connection (i.e. not in code).
This process creates a connection object and an OleDbAdapter object (which I
named estateOleAdapter as you can see in my web service code). I also tried
to establish the connection and adapter in code but continue to have the same
problem.

Whenever I try to consume this service (using a web or even a windows
application this exception comes up):

System.ServiceModel.FaultException was unhandled by user code
Message="System.Web.Services.Protocols.SoapException: Server was unable to
process request. ---> System.NullReferenceException: Object reference not set
to an instance of an object. at
WebServiceLiverpoolUKEstateAgents.Service1.GetEstateAgents() in
C:\Hope\modules i teach\web services\handout
exercises\chapter5\WebServiceLiverpoolUKEstateAgents\WebServiceLiverpoolUKEstateAgents\LiverpoolUKEstateAgents.asmx.vb:line
29 --- End of inner exception stack trace ---"
Source="mscorlib"
StackTrace:
Server stack trace: at
System.ServiceModel.Channels.ServiceChannel.HandleReply(ProxyOperationRuntime
operation, ProxyRpc& rpc) at
System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean
oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs,
TimeSpan timeout) at
System.ServiceModel.Channels.ServiceChannel.Call(String action, Boolean
oneway, ProxyOperationRuntime operation, Object[] ins, Object[] outs) at
System.ServiceModel.Channels.ServiceChannelProxy.InvokeService(IMethodCallMessage
methodCall, ProxyOperationRuntime operation) at
System.ServiceModel.Channels.ServiceChannelProxy.Invoke(IMessage message)
Exception rethrown at [0]: at
System.Runtime.Remoting.Proxies.RealProxy.HandleReturnMessage(IMessage
reqMsg, IMessage retMsg) at
System.Runtime.Remoting.Proxies.RealProxy.PrivateInvoke(MessageData& msgData,
Int32 type) at
ClientLiverpoolUKEstateAgents.WebServiceLiverpoolUKEstateAgents.Service1Soap.GetEstateAgents()
at
ClientLiverpoolUKEstateAgents.WebServiceLiverpoolUKEstateAgents.Service1SoapClient.GetEstateAgents()
in C:\Hope\modules i teach\web services\handout
exercises\chapter5\ClientLiverpoolUKEstateAgents\ClientLiverpoolUKEstateAgents\Service
References\WebServiceLiverpoolUKEstateAgents\Reference.vb:line 59 at
ClientLiverpoolUKEstateAgents._Default.form1_Load(Object sender, EventArgs e)
in C:\Hope\modules i teach\web services\handout
exercises\chapter5\ClientLiverpoolUKEstateAgents\ClientLiverpoolUKEstateAgents\Default.aspx.vb:line
19 at System.Web.UI.Control.OnLoad(EventArgs e) at
System.Web.UI.Control.LoadRecursive() at
System.Web.UI.Control.LoadRecursive() at
System.Web.UI.Page.ProcessRequestMain(Boolean includeStagesBeforeAsyncPoint,
Boolean includeStagesAfterAsyncPoint)
InnerException:

This is the code (inserted in a command’s click procedure) that I used to
consume the service:

Dim eaService As New WebServiceLiverpoolUKEstateAgents.Service1SoapClient

'Supply the dataset to become the DataGrid's datasource
'dgEstateAgents.DataSource = eaService.GetEstateAgents

dgEstateAgents.DataSource = eaService.GetEstateAgents

'Bind the data to the datagrid by transferring
'it from the dataset to the datagrid

dgEstateAgents.DataBind()

The dgEstateAgents is the name of the datagrid which I created using the
GUI. When adding a reference, I tried “Add Service Reference†and I also
tried “Add Web Referenceâ€, neither worked.

To ensure that my web service is well connected to my Access database, I
would sometimes click on the Data icon on the menu bar and select Preview
Data and then click to populate the dataset. Sometimes this results in the
display of the database’s table. However, when I try to do same thing other
times I get a window that says: "Value cannot be null. Parameter name:
serviceProvider" which leads me to conclude that the dataset is empty. If I
close that web service and relaunch it I don’t get this "Value cannot be
null. Parameter name: serviceProvider" error!!


In either case, my client application halts on this line
dgEstateAgents.DataSource = eaService.GetEstateAgents
every time I try to consume the service and throws the exception listed above.

The operation system I use is Vista (business edition).

When I used VS 2005 in the past I had no such errors and the web service was
consumed without any problems. So, I am really clueless here!
 

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