Re: [Pyobjc-dev] NSUndoManager.prepareWithInvocationTarget_

[Ronald O. <ous...@ci...>]

On Monday, Dec 30, 2002, at 01:17 Europe/Amsterdam, David Eppstein 
wrote:

> Should
> NSUndoManager.prepareWithInvocationTarget_(x).some_Method_(arg,arg)
> work (where x is any object and some_Method_ is a selector handled by 
> x)?

I expected that this would work, but it clearly doesn't. This seems to 
be caused by a misunderstanding on my part of the semantics of 
'NSObject.respondsToSelector:'. I expected that this returns true 
whenever 'NSObject.methodSignatureForSelector:' returns a non-nil 
value, but it doesn't.

----- test.py --------

from Foundation import *

class Foo (NSObject):
     def test_(self, foo):
         print foo

x = Foo.new()

m = NSUndoManager.new()
m.prepareWithInvocationTarget_(x)
print x.respondsToSelector_('test:') # Prints 1
print m.respondsToSelector_('test:') # Prints 0?
print x.methodSignatureForSelector_('test:') # Prints 
<NSMethodSignature ...>
print m.methodSignatureForSelector_('test:') # Prints same value
print m.methodSignatureForSelector_('foo:')  # Raises AttributeError?
m.test_("hello world")
m.undo()

---- end of test.py ----

As I wrote earlier I expected 'm.respondsToSelector_('test:') to return 
1. Because it doesn't the bridge assumes that 'm' won't respond to 
'test_'. Fixing this design-error won't be too hard.

I'm not yet sure why 'm.methodSignatureForSelector_("foo:")' raises an 
exception (it has nothing to do with the NSUndoManager class, 
'x.methodSignatureForSelector_("foo:")' raises the same exception.

Ronald