[Pyobjc-dev] Problem with PyObjc-1.1b2 and key value binding

[<mat...@da...>]

Greetings,

This is my first post to this group, possibly because only recently I've 
touched the bleeding edge of PyObjc on Panther ;-). Otherwise, I'm greatly 

impressed by the bridge and its huge (magically working) functionality. It 

means I can now continue my NEXTSTEP 3.3 style programming (yes, yes I 
still have an Intel box running), yet under much better conditions. Though 

Objective-C is not that bad for GUI programming (at least it is much 
better suited than C++), Python offers even more pleasures. 

First of all, many thanks especially to Bill, Bob, Jack and Ronald, to 
name only the four prominent names that come up to my mind. Sorry that I 
can't mention all the many others explicitly. Thank you all!

Here comes my problem: Last week I dipped my nose a little into Apple's 
key-kalue binding (KVB) paradigm offered on Panther. Though documentation 
is scarce by now, it appears to me that this is indeed a major advance 
compared to the AppKit of the good old NEXTSTEP days. I mean advance in 
the sense of "simplifying your own code and reducing the time to create 
it". 

So I played around with KVB using PyObjc 1.0. Unfortunetely, it did not 
really work well (I ran into segmentation faults) , so I gave PyObjc-1.1b2 

a try. The nasty segmentation faults went away and all seemed to work as 
expected, but now I've got problems with access to Objective-C variables 
(outlets in particular). The normal way, e.g. 'obj.outlet', does no longer 

 work. Apparently as soon as some controller watches 'obj'. However,  I 
can use PyObjCTools.KeyValueCoding.getKey to obtain access.

Here are instructions to create a barebones example that exhibit the 
problem:
 

Create a new Cocoa-Python Application called 'Test' in Project Builder
Open Main.nib in Interface Builder
Drag an object controller instance from the palette to the applicationn's 
nib file.
Connect  the contoller's 'content' outlet  to the application's delegate.
Add key 'buttonName' to the controller keys.


Drag a button to the application's window.
Select 'Bindings' in the inspector.
Unfold parameters 'title'.
Select 'buttonName' from the model key path pulldown menu.


Edit the class 'TestApplicationDelegate' in Interface Builder by adding an 

outlet 'myOutlet'.
Connect the outlet 'myOutlet' of the TestApplicationDelegate instance to 
the button in the main window.


Edit the file TestAppDelegate.py to contain the following:

from Foundation import NSLog
from PyObjCTools import NibClassBuilder
from PyObjCTools.KeyValueCoding import getKey

NibClassBuilder.extractClasses("MainMenu")
class TestAppDelegate(NibClassBuilder.AutoBaseClass): 
    def applicationDidFinishLaunching_(self, aNotification):
       print "usual attribute access"
       try:
         print "myOutlet:", self.myOutlet 
       except Exception, what:
         print
         print what
       print "access using getKey"
       print "myOutlet:", getKey(self, 'myOutlet')
       NSLog( "Application did finish launching." )
 
    def buttonName(self):
      return 'Hello'

Save the nib file, build and run the application

The button shows the name 'Hello', thanks to key/value binding'. However, 
I can't access outlets in the usual way anymore. I get the following 
output in the console:

usual attribute access
myOutlet:
'NSNotifying_PyKVBAppDelegate' object has no attribute 'myOutlet'
access using getKey
myOutlet: <NSButton: 0x3d23a0>
2004-05-03 09:32:56.488 PyKVB[4196] Application did finish launching.

In order to demonstrate that this unexpected behavior has to to with KVB, 
I can uncheck the 'Bind' feature for the button's title. 

After I saved the nib file and restarted the application, I now get:

usual attribute access
myOutlet: <NSButton: 0x3d1ff0>
access using getKey
myOutlet: <NSButton: 0x3d1ff0>
2004-05-03 09:53:14.638 PyKVB[4202] Application did finish launching.

Of course, the name of the button is no longer 'Hello', because key value 
observing is now inactive. I've somewhere encounterd the term 
'isa-swizzling'. Maybe the problem has to do with that.

Regards,

Matthias

--
Matthias Oberlaender

DaimlerChrysler AG 
Research and Technology 
Information and Communication 
RIC/AP (Machine Perception) 
P.O. Box 2360 
D-89013 Ulm