How to re login after a failed login

Question

Using .Net Connector 3.0\Compiled with .NET Framework 2.0 and MS Visual Studio 2008, C#
Hello All,
I created an application where the user can input SAP user name and password in a dialog. Then it connects to SAP and executing some RFC. Working fine.
When the user put in a wrong SAP username or password I get an exception. OK.
But what do I have to do, to let him login again with the correct username and password.
Here is my coding:
                IDestinationConfiguration config = new myBackendConfig(); // provides all connection parameters including user/pwd
                RfcDestination prd = RfcDestinationManager.GetDestination(config.GetParameters(connId));
                RfcRepository repo = prd.Repository;
When I call this second time with correct user/password, then the prd.Repository will run into an exception with message:
"Der Wert darf nicht NULL sein.\nParametername: key" (german)
My translation: "Value must not be NULL.\nParameter name: key".
Any help would be appreciated!
Regards,
Peter

Answer 1

Hello Peter,
I was struggling with the same issue.
NCo provides an delegate for handling change events: RfcDestinationManager.ConfigurationChangeHandler. But I found no documentation about this and could'n get it running.
Here is my workaround:
For destination configuration use the way as described in NCo_30_Overview.pdf (page 7 and 8).
If the compiler warns you, that the event is never used, just add the following line to MyBackendConfig:
private void ConfigurationChangedEventDummyCall() { ConfigurationChanged(null, null); }
Change your coding as follows:
IDestinationConfiguration config = new MyBackendConfig();
RfcDestinationManager.RegisterDestinationConfiguration(config);
RfcDestination prd = RfcDestinationManager.GetDestination("PRD_000");
before you try to get the Repository, execute a Ping and catch the Exception:
try...
prd.Ping();
This prevents you from getting the "Der Wert darf nicht NULL sein" error on the second call.
If Ping fails, unregister the configuration, change username and/or password, create a new config and register again.
catch...
RfcDestinationManager.UnregisterDestinationConfiguration(config);
// change config here... (prompt for username / password)
config = new MyBackendConfig();
RfcDestinationManager.RegisterDestinationConfiguration(config);
RfcDestination prd = RfcDestinationManager.GetDestination("PRD_000");
again
prd.Ping();
If the second ping is working, logon was ok and you can continue and get the Repository without an error.
Regards,
Ingo
Edited by: Ingo Frank on Sep 19, 2011 4:24 PM