How to: Catch Exceptions Thrown from CLR Objects

Applies To: Microsoft Dynamics AX 2012 R3, Microsoft Dynamics AX 2012 R2, Microsoft Dynamics AX 2012 Feature Pack, Microsoft Dynamics AX 2012

In Microsoft Dynamics AX, when your X++ code calls .NET framework methods it is important that your code be designed to handle exceptions. When your code catches exceptions it can relay valuable diagnostic information to the user.

Processing a CLRException

The X++ code sample in this section calls methods that are in a .NET assembly. As we recommend, these calls are inside a try block.

To demonstrate the exception handling, the sample purposely tries to create a Windows event log source a second time, which causes a duplicate name. The duplicate causes the system to throw a .NET exception. The sample shows how to obtain detailed diagnostic information from that exception.

The sample has a catch block for the X++ enum value Exception::CLRError. In that catch block the following steps are taken:

1. ClrInterop::getLastException is called.

2. ex.get_InnerException is called.

X++ Code Sample

The following X++ code sample demonstrates how to handle exceptions that are thrown from .NET methods.

// X++
static void JobCreateEventLog(Args _args)
{
    #define.LogSource("Dynamics AX")
    #define.LogName("Dynamics AX Log")
    System.Exception ex;
    System.Diagnostics.EventLog eventLog;
    ;
    try
    {
        // Create the log if it does not already exist.
        if (!System.Diagnostics.EventLog::SourceExists(#LogSource))
        {
            System.Diagnostics.EventLog::CreateEventSource(#LogSource, #LogName);
        }

        // Next line is an intentional bug for this demonstration of CLR exceptions.
        // It causes an exception due to a name duplication.
        System.Diagnostics.EventLog::CreateEventSource(#LogSource, #LogName);

        // Write to this newly created log source, if the process gets this far.
        eventLog = new System.Diagnostics.EventLog();
        eventLog.set_Source(#LogSource);
        eventLog.WriteEntry
            ("The exception should prevent this line from appearing in the Windows event viewer.",
            System.Diagnostics.EventLogEntryType::Warning
            );
    }
    catch (Exception::CLRError)
    {
         ex = ClrInterop::getLastException();
         if (ex != null)
         {
            ex = ex.get_InnerException();
            if (ex != null)
            {
                error(ex.ToString());
            }
        }
    }
    // Clean up.
    System.Diagnostics.EventLog::DeleteEventSource(#LogSource, #LogName);
}
/*** Messages displayed in the Infolog:
System.ArgumentException: Source Dynamics AX already exists on the local computer.
   at System.Diagnostics.EventLog.CreateEventSource(EventSourceCreationData sourceData)
   at System.Diagnostics.EventLog.CreateEventSource(String source, String logName)
***/

See also

Exception Handling with try and catch Keywords

.NET Interop from X++

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