Hello,

Does anyone know of any example code for the FPObserver interface? Preferable with Collections.

Thank you.

bsquared wrote

Hello, Does anyone know of any example code for the FPObserver interface? Preferable with Collections.

Sure, see attached. It's very basic, but shows the functionality.

NOTE:
I used latest 2.7.1 compiler, where some base classes in the RTL support the IFPObserved interface.

And the demo output is as follows:

------------------------------------
$ ./fpobserver_demo
TStringList has changed [ooChange]
TStringList has changed [ooChange]
TStringList has changed [ooChange]
[ooFree] detected so we should detach ourselves
------------------------------------

This does raise some points of interest though.

1) I would probably surface the IFPObserver methods to Public. Though there is good arguments to not do it either - thus you are forced to use correct interface usage... via Supports(), getting a interface pointer back, and using that interface pointer to make method calls.

2) Even though I did two Add() calls and one Delete() call, TStringList reported the operation as simply ooChanged. Correct, but not very precise. After all, we also have ooAdd, ooDelete operation states we could work with.

3) My personal preference is that the Observed automatically detaches Observers in the destructor. But this is just a personal preference in my own code.

Regards,
- Graeme -

Note: Although the IFPObserver and IFPObserved interfaces are defined as Corba interfaces you should be able to use "YourInstance as IFPObserver" instead of "Supports()".

Regards,
Sven

Thank you for you example.

I have had no exposure to CORBA. Your example gave me just what I needed.

Is there an advantage?

Sven Barth wrote

Note: Although the IFPObserver and IFPObserved interfaces are defined as Corba interfaces you should be able to use "YourInstance as IFPObserver" instead of "Supports()".

Correct, but my preference is to use Supports() - it makes the code easier to read and follow.

Regards,
- Graeme -

bsquared wrote

> Is there an advantage?

No difference, other than that I find Supports() easier to read.

G.

bsquared wrote

I have had no exposure to CORBA. Your example gave me just what I needed.

CORBA style interface are simply interfaces without reference counting - so you are in control of when to free instances.

CORBA style interfaces (as seen in FPC) are far from a complete CORBA ORB (Object Request Broker) implementation like the one included with Delphi.

So ignore the name CORBA, and just think of it as COM interfaces without reference counting. Oh, and CORBA interfaces don't descend from IUnknown & IInterface.

Regards,
- Graeme -

Thanks again.