[MacRuby-devel] NSManagedObject being returned in delegate as Pointer

[Dr Nic Williams]

At least I know to look out for (void *) and pass objects around outside them.

Thx for the help.

On Wed, Dec 31, 2008 at 2:08 PM, Laurent Sansonetti
<lsansonetti at apple.com> wrote:
> Oh I see, indeed. The problem here is that the contextInfo argument has a
> "void *" type, so the runtime does not know that you passed an Objective-C
> object for it via an implicit cast.
>
> In this case, we need to introduce a new method on Pointer to allow you to
> change its type. In RubyCocoa, the method is #cast_as, I will probably use
> the same name.
>
> In practice, you should avoid passing objects as context to methods like
> this one, because their implementation won't keep a GC reference to them, so
> they might disappear during a collection cycle.
>
> Laurent
>
> On Dec 30, 2008, at 7:52 PM, Nic Williams wrote:
>
>> Calling recipe[0] results in this error:
>>
>> AppDelegate.rb:157:in `[]': can't convert C/Objective-C value
>> `0x8004676a0' of type `v' to Ruby object (ArgumentError)
>>
>> I'm not sure what this means. I've played around with the Pointer
>> class and I can get this error a lot.
>>
>> The original ObjC signature that is called to open the NSOpenPanel is:
>>
>> - (void)beginSheetForDirectory:(NSString *)path file:(NSString *)name
>> modalForWindow:(NSWindow *)docWindow modalDelegate:(id)modalDelegate
>> didEndSelector:(SEL)didEndSelector contextInfo:(void *)contextInfo
>>
>> Where the recipe (NSManagedObject_Recipe) is passed into a (void
>> *)contextInfo. Do I need to do anything fancy for this? Is the (void
>> *) causing the Pointer creation?
>>
>> On Wed, Dec 31, 2008 at 1:46 PM, Laurent Sansonetti
>> <lsansonetti at apple.com> wrote:
>>>
>>> On Dec 30, 2008, at 7:32 PM, Nic Williams wrote:
>>>
>>>> In this code sample: http://gist.github.com/41855 I am getting a
>>>> Pointer instance instead of an NSManagedObject_Recipe instance (from
>>>> Core Data). Subsequently the setValue:forKey: call at the end of the
>>>> delegate/callback method fails.
>>>>
>>>> The top method addImage(sender) launches an NSOpenPanel, which
>>>> delegates to the second/last method
>>>> addImageSheetDidEnd:returnCode:contextInfo: when the panel is closed.
>>>>
>>>> But instead of passing through the NSManagedObject_Recipe instance to
>>>> the contextInfo: recipe value, I am getting a Pointer.
>>>>
>>>> Is this correct? Or how do I get my NSManagedObject_Recipe instance
>>>> from the Pointer. MacRuby src for Pointer class doesn't suggest it has
>>>> any methods for getting the pointed-to thing.
>>>>
>>>>  rb_cPointer = rb_define_class("Pointer", rb_cObject);
>>>>  rb_undef_alloc_func(rb_cPointer);
>>>>  rb_define_singleton_method(rb_cPointer, "new_with_type",
>>>> rb_pointer_new_with_type, 1);
>>>>  rb_define_method(rb_cPointer, "assign", rb_pointer_assign, 1);
>>>>  rb_define_method(rb_cPointer, "[]", rb_pointer_aref, 1);
>>>
>>> You can do pointer[0] to dereference it.
>>>
>>> A Pointer object can be created from a C array of elements, which is why
>>> Pointer responds to #[] (so that you can dereference a particular slot).
>>>
>>> Laurent
>>> _______________________________________________
>>> MacRuby-devel mailing list
>>> MacRuby-devel at lists.macosforge.org
>>> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
>>>
>>
>>
>>
>> --
>> Dr Nic Williams
>> iPhone and Rails consultants - http://mocra.com
>> Fun with iPhone/Ruby/Rails/Javascript - http://drnicwilliams.com
>> * Surf Report for iPhone - http://mocra.com/projects/surfreport/ *
>> _______________________________________________
>> MacRuby-devel mailing list
>> MacRuby-devel at lists.macosforge.org
>> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
>
> _______________________________________________
> MacRuby-devel mailing list
> MacRuby-devel at lists.macosforge.org
> http://lists.macosforge.org/mailman/listinfo.cgi/macruby-devel
>



-- 
Dr Nic Williams
iPhone and Rails consultants - http://mocra.com
Fun with iPhone/Ruby/Rails/Javascript - http://drnicwilliams.com
* Surf Report for iPhone - http://mocra.com/projects/surfreport/ *