Re: [Pyobjc-dev] Confusing crash that's fixed by adding NSBeep()

[Ronald O. <ron...@ma...>]

On 20 May, 2010, at 21:52, Scott Harris wrote:

> Thanks. Changing the method name to something other than action fixes the issue. Is action a bad choice for a method in general?

I'd say so purely design/code smell view: 'action' doesn't communicate what the method will do (at least not unless it returns an action of some sort).

That said, the crash your having is a bug in PyObjC as I expected.  The bug has two levels: first of all PyObjC thinks there is an informal protocol that describes the interface of an action method because a class in AppKit defines its action method in a category. Secondly PyObjC shouldn't use its knowlegde about informal protocols to override the method signature of method that is defined in ObjC.

This last bit causes the crash: your ObjC method is a method dat returns nothing ("-(void)action"), while the action method in the PyObjC metadata returns a selector ("-(SEL)action"). This causes PyObjC to treat some arbitrary value on the stack as a SEL, which is basicly a C string and that causes a EXC_BAD_ACCESS.

Ronald

> 
> -Scott
> On May 15, 2010, at 11:24 AM, Ronald Oussoren wrote:
> 
>> 
>> On 14 May, 2010, at 8:40, Scott Harris wrote:
>> 
>>> I've got this obj-c object in a simple demo program:
>>> 
>>> 
>>> @implementation junker
>>> -(id) init
>>> {
>>>     [super init];
>>>     NSLog(@"initing");
>>>     [self action];
>>>     return self;
>>> }
>>> -(void) action
>>> {
>>>     NSLog(@"junk");
>>>     //NSBeep();
>>> }
>>> @end
>>> 
>>> I call it from Python in my App delegate like this:
>>> 
>>> from Foundation import *
>>> from AppKit import *
>>> 
>>> class PyObjCTestAppDelegate(NSObject):
>>>     def applicationDidFinishLaunching_(self, sender):
>>>         NSLog("Application did finish launching.")
>>>         self.a=junker.alloc().init()
>>> 
>>>     def awakeFromNib(self):
>>>         NSLog("Awoke from NIB")
>>> 		
>>>     @objc.IBAction
>>>     def buttonPress_(self, sender):
>>>         NSLog("Button pressed!")
>>>         self.a.action()
>>> 
>>> The funny thing is that the program crashes when I press the button that calls buttonPress iff NSBeep is commented out, but runs fine if the NSBeep is uncommented. Strange.
>>> 
>>> Here's the console output:
>>> 2010-05-14 00:39:23.924 PyObjCTest[99096:a0f] Awoke from NIB
>>> 2010-05-14 00:39:24.006 PyObjCTest[99096:a0f] Drawing
>>> 2010-05-14 00:39:24.069 PyObjCTest[99096:a0f] Application did finish launching.
>>> 2010-05-14 00:39:24.070 PyObjCTest[99096:a0f] initing
>>> 2010-05-14 00:39:24.070 PyObjCTest[99096:a0f] junk
>>> 2010-05-14 00:39:29.781 PyObjCTest[99096:a0f] Button Pressed
>>> 2010-05-14 00:39:29.782 PyObjCTest[99096:a0f] junk
>>> Program received signal:  “EXC_BAD_ACCESS”.
>>> sharedlibrary apply-load-rules all
>>> 
>>> Any ideas?
>> 
>> The code looks correct, but indeed crashes.  I'm looking into this, at first glance it seems that PyObjC is confused about the return type for [junker -action], and that's probably caused by the metadata files. 
>> 
>> One quick way to work around this: rename 'action' to something else.
>> 
>> Ronald
>> 
>