How to get Exception Error Code in C#

Solution 1:

You can use this to check the exception and the inner exception for a Win32Exception derived exception.

catch (Exception e) {  
    var w32ex = e as Win32Exception;
    if(w32ex == null) {
        w32ex = e.InnerException as Win32Exception;
    }    
    if(w32ex != null) {
        int code =  w32ex.ErrorCode;
        // do stuff
    }    
    // do other stuff   
}

Starting with C# 6, when can be used in a catch statement to specify a condition that must be true for the handler for a specific exception to execute.

catch (Win32Exception ex) when (ex.InnerException is Win32Exception) {
    var w32ex = (Win32Exception)ex.InnerException;
    var code =  w32ex.ErrorCode;
}

As in the comments, you really need to see what exception is actually being thrown to understand what you can do, and in which case a specific catch is preferred over just catching Exception. Something like:

  catch (BlahBlahException ex) {  
      // do stuff   
  }

Also System.Exception has a HRESULT

 catch (Exception ex) {  
     var code = ex.HResult;
 }

However, it's only available from .NET 4.5 upwards.

Solution 2:

Building on Preet Sangha's solution, the following should safely cover the scenario where you're working with a large solution with the potential for several Inner Exceptions.

 try
 {
     object result = processClass.InvokeMethod("Create", methodArgs);
 }
 catch (Exception e)
 {
     // Here I was hoping to get an error code.
     if (ExceptionContainsErrorCode(e, 10004))
     {
         // Execute desired actions
     }
 }

...

private bool ExceptionContainsErrorCode(Exception e, int ErrorCode)
{
    Win32Exception winEx = e as Win32Exception;
    if (winEx != null && ErrorCode == winEx.ErrorCode) 
        return true;

    if (e.InnerException != null) 
        return ExceptionContainsErrorCode(e.InnerException, ErrorCode);

    return false;
}

This code has been unit tested.

I won't harp too much on the need for coming to appreciate and implement good practice when it comes to Exception Handling by managing each expected Exception Type within their own blocks.

Solution 3:

You should look at the members of the thrown exception, particularly .Message and .InnerException.

I would also see whether or not the documentation for InvokeMethod tells you whether it throws some more specialized Exception class than Exception - such as the Win32Exception suggested by @Preet. Catching and just looking at the Exception base class may not be particularly useful.