Recipe 7.9. Handling User-Defined HRESULTs

Problem

A COM object can return a user-defined hrESULT or an hrESULT that has no mapping to a managed exception type. You wish to handle these returned hrESULTs in a more specific manner.

Solution

The following code fragment illustrates the handling of user-defined COM/COM+ exceptions:

	try
	{
	    CallCOMMethod( );
	}
	catch (System.Runtime.InteropServices.COMException ce)
	{
	    switch ((uint)ce.ErrorCode)
	    {
	        case 0x80042000:
	            // Handle specific user-defined COM/COM+ exception here.
	            break;
	        case 0x80042001:
	            // Handle specific user-defined COM/COM+ exception here.
	            break;
	        default:
	            // Handle any other specific user-defined COM/COM+
	            // exceptions here.
	            break;
	    }
	}
	catch (Exception e)
	{
	    // Handle all other exceptions here.
	}

Discussion

Handle any user-defined exceptions that are unique to a specific COM/COM+ component by trapping the COMException exception. This class reflects COM/COM+ hrESULTs that have no mapping to managed exceptions.

The COMException has a property, ErrorCode, in addition to those properties in the base Exception class. This property contains the HRESULT value that the COM/COM+ object returned. Another difference between COMException and Exception is that the InnerException property of a COMException object will always be null.

See Also

See the "Error Raising and Handling Guidelines" and "Handling COM Interop Exceptions" topics in the MSDN documentation.