[news.eclipse.tools.gef] Re: Connecting connections in the Shape example

[Adrian Gygax <adrian.gygax@xxxxxxx>]

Thanks for pointing out the problem with the coordinates, Steve!

Meanwhile, I finally found and solved the problem.

It seems that ConnectionAnchors for Connections must not extend 
AbstractConnectionAnchor but ConnectionAnchorBase. 
AbstractConnectionAnchor adds the Anchor as an AncestorListener to its 
owner. This causes an infinite loop of revalidation because 
PolylineConnection listens to the anchor and the anchor listens to the 
PolylineConnection. Somehow PolylineConnection says it has moved which 
in turn causes the anchor to say it has moved which in turn causes 
PolylineConnection to say it has moved, and so on:

PolylineConnection.revalidate() -> ... -> 
AbstractConnectionAnchor.ancestorMoved(PolylineConnection) -> 
PolylineConnection.anchorMoved(AbstractConnectionAnchor) -> 
PolylineConnection.revalidate()

The attached archive contains the Shapes example extended by the 
possibility to connect connections to each other. Especially, it 
contains a PolylineConnectionAnchor which returns the midpoint of the 
connection as the anchor location. The modifications are documented in 
the code.

I'll try to create a Howto for connecting connection in the Wiki when I 
have some free time.

Best regards
Adrian

Steven Shaw wrote:
> One thing I noticed is that you're not returning the point in absolute
> coordinates.  The points in the polyline connection are in relative
> coordinates.  Anchors always operate in absolute coordinates.  You need to
> make a call to:
>
> getOwner().translateToAbsolute(midpoint);
> return midpoint;
>
> -Steve
>
> "Adrian Gygax" <adrian.gygax@xxxxxxx> wrote in message
> news:du49el$6cg$1@xxxxxxxxxxxxxxxxxxxx
> > Hi!
> >
> > I'm trying to extend the Shape example so there can be Connections
> > connecting Connections. This is what I did so far:
> >
> > - Pulled up Connection handling stuff from Shape to a new Class
> > "ConnectableElements". Both, Shape and Connection extend this class
> > - Adapted ConnectionCreateCommand to take ConnectableElements instead of
> > only Shapes
> > - In ConnectionEditPart I'm installing a GraphicalNodeEditPolicy under
> > the EditPolicy.GRAPHICAL_NODE_ROLE which I copied from ShapeEditPart
> > - I wrote a custom ConnectionAnchor which returns the midpoint of a
> > PolylineConnection as Location
> >
> > Now I have a similar problem like Brian Fernandez in the "Connecting
> > connections to connections ..." thread: As soon as I try to connect a
> > Connection the tool ends up in an endless loop calling getLocation()
> > from my CustomConnectionAnchor. If I use an XYAnchor instead, the
> > endless loop vanishes (But the resulting connection's display is useless
> > because start/end points are always at the same place, of course).
> > Unfortunately, I don't understand what he did to solve the problem. Can
> > anybody help me? I attached my extended Shapes example for reference.
> >
> > Best regards,
> > Adrian

Attachment: ConnectingConnectionsShapesExampleWorking.zip
Description: Zip compressed data