[Gtk-sharp-list] Handling errors when generating binding code for asynchronous APIs

[Philip Van Hoof]

That might indeed solve it. Then I can still make a ToException in my
TError.cs type. Right?

Here are the diffs:
http://tinymail.org/trac/tinymail/changeset/3392
http://tinymail.org/trac/tinymail/browser/trunk/bindings/dotnet/tny/TError.cs

Thanks


On Sun, 2008-02-10 at 10:30 -0600, Mike Kestner wrote:
> On Sun, 2008-02-10 at 15:27 +0100, Philip Van Hoof wrote:
> 
> > The GError based error being passed to the callback (which in C is a
> > function pointer typedeffed as TnyGetMsgCallback) is not being converted
> > to an Exception type.
> 
> First, I'm not convinced there's a real advantage to using an exception
> for this.  Throwing it is only going to result in the program exiting in
> the virtual method marshaler's try/catch or if the user has connected to
> GLib.ExceptionManager they'll get the exception there.  So throwing the
> exception would just be additional overhead since they can just call the
> error handler directly from the method implementation itself.
> 
> > My goal is to wrap the "IntPtr err" (which is the GError pointer in C)
> > with a factory's Create method that will create me the right managed
> > exception:
> > 
> > public class Tny.ExceptionFactory
> > {
> > 	static Tny.TException Create (IntPtr gerror) {
> > 		// Pseudo, to get the type I'll indeed need to make
> > 		// a small piece of glue code in C ...
> > 		if (gerror->type == TNY_ERROR_THIS)
> > 			return new Tny.ThisException (gerror);
> > 		if (gerror->type == TNY_ERROR_THAT)
> > 			return new Tny.ThatException (gerror);
> > 		...
> > 	}
> > }
> 
> It sounds to me like an error string to enumeration mapping would be
> equally as useful.  Regardless, if you are set on creating exceptions
> for these, there is already a built in way to hook in a marshaling
> method like the above to GAPI.
> 
> You will need to alter the type of the parameter to something GAPI
> doesn't handle automatically, like TError, using metadata.  Also using
> metadata, you need to add a generatable mapping for TError.  Two
> possibilities are:
> 
> <symbol type="manual" cname="TError" name="Tny.Error"/></add-node>
> 
> This assumes the existence of a Tny.Error type which has an IntPtr
> Handle prop to marshal to native and a static Tny.Error New (IntPtr)
> method to marshal from native.
> 
> As an alternative you could use MarshalGen via:
> 
> <symbol type="marshal" cname="GdkEvent" name="Gdk.Event"
> marshal_type="IntPtr" call_fmt="{0}.Handle" from_fmt="Gdk.Event.GetEvent
> ({0})" />
> 
> Which gives a bit more control over the way you implement your
> marshaler.
> 
> You can add either of the above symbols to your API file with an
> add-node rule in metadata:
> 
> <add-node path="/api">...
> 
> Mike
> 
> 
> 
-- 
Philip Van Hoof, freelance software developer
home: me at pvanhoof dot be 
gnome: pvanhoof at gnome dot org 
http://pvanhoof.be/blog
http://codeminded.be