Re: Variant arguments & com function calls

We should probably add this to COMException or COMError (Why do we have
both?)

public static final int DISP_E_PARAMNOTFOUND = 0x80020004;


For now you can use this to create a variant for optional arguments (code
below not tried by me...):

Variant missing = new Variant();
v.vt = VarType.VT_ERROR;
v.scode = 0x80020004;


If that works for you, then we should probably add

public class Variant {
...
public static final Variant MISSING = new Variant();
static {
  MISSING.vt = VarType.VT_ERROR;
  MISSING.scode = COMException.DISP_E_PARAMNOTFOUND;
}

So that you can use Variant.MISSING for optional VARIANT args.


Robert


-----Original Message-----
From: Discussion of Java/Win32/COM integration with Jawin
[mailto:JAWIN@xxxxxxxxxxxxxxxxxxx] On Behalf Of Morten Andersen
Sent: Saturday, July 31, 2004 2:16 PM
To: JAWIN@xxxxxxxxxxxxxxxxxxx
Subject: Re: [JAWIN] Variant arguments & com function calls

Hi Alex

Alex Kotchnev wrote:

[SNIP - well documented questions]

>
>
> To summarize the questions questions:
> 1. When there is a function that takes a Variant, which field in Variant
> would have to be set ? I understand that maybe there is no general rule
for
> this, but at least a hint would be helpful...

It should generally not be necessary to generate instances of
org.jawin.Variant. Most (if not all) marshalling will be handled
correctly by the automatic marshalling and the dispatch coercion
mechanism. Eg. java.lang.Integer -> VT_UI4.

I have recently refactored and documented a lot of this marshalling, so
I suggest you try to check out the latest CVS-release by following the
guidelines here http://jawinproject.sourceforge.net/jawindeveloper.html.
Besides the javadoc for org.jawin.DispatchPtr and org.jawin.Variant you
should check the docs/jawinuserguide_dispatch.html documentation (I have
just made checkins 5 minutes ago, which should be available on the
public CVS-server in approximately 5 hours).

> 2. Is there an equivalent to the C# Type.Missing, or some other way to
> indicate that the argument has to take its default value in the Com
> function invocation ?

We don't have that pt. You can try with "null", which get marshalled
into VT_NULL, but I assume we need to marshal into VT_EMPTY to get this
to work? But at least it sounds like it is something we have to support.

Hope this helps you a little bit. And as a sidenote, as I don't know
exactly what you are trying to do with Excel, but have you checked the
POI project http://jakarta.apache.org/poi/, for writing/reading Excel
files?.

Best Regards
Morten