On 12 Mar 2012, at 16:57, Greg Parker wrote:
> On Mar 10, 2012, at 11:05 PM, Antonio Nunes wrote:
>> In the latest public release of my software, I used method swizzling to
>> force creation of my subclass when the system tries to create instances of
>> its superclass. However, I have received a very few reports where apparently
>> instances of the superclass are still created, and wreak havoc (i.e. they
>> cause a crash). In what way is it still possible for instances of the
>> superclass to be created?
>>
>> + (void)initialize
>> {
>> // To force PDFDocuments to be created as NMD_PDFDocuments
>> // Necessary because of an issue with PDFThumbnailView
>> Method originalMethod = class_getClassMethod([PDFDocument class],
>> @selector(allocWithZone:));
>> Method superMethod =
>> class_getClassMethod(class_getSuperclass([PDFDocument class]),
>> @selector(allocWithZone:));
>>
>> Method replacedMethod = class_getClassMethod([PDFDocument class],
>> @selector(allocWithZoneReplacement:));
>> if (superMethod == originalMethod) {
>> class_addMethod(object_getClass([PDFDocument class]),
>> @selector(allocWithZone:),
>>
>> method_getImplementation(replacedMethod),
>>
>> method_getDescription(replacedMethod)->types);
>> }
>>
>> // To force PDFPages to be created as NMD_PDFPage
>> originalMethod = class_getClassMethod([PDFPage class],
>> @selector(allocWithZone:));
>> superMethod = class_getClassMethod(class_getSuperclass([PDFPage
>> class]), @selector(allocWithZone:));
>>
>> replacedMethod = class_getClassMethod([PDFPage class],
>> @selector(allocWithZoneReplacement:));
>> if (superMethod == originalMethod) {
>> class_addMethod(object_getClass([PDFPage class]),
>> @selector(allocWithZone:),
>>
>> method_getImplementation(replacedMethod),
>>
>> method_getDescription(replacedMethod)->types);
>> }
>> }
>
> Note that your code does nothing if PDFPage or PDFDocument themselves
> override +allocWithZone:. Do you know whether that may be the case?
I don't think that is the case. The code works fine almost always. If the
superclasses themselves overrode +allocWIthZone: I suppose my code would never
run, right? I think I've only seen a single source with a few crash reports
where PDFPages had been created instead of NMD_PDFPages. So, doesn't that
suggest that my code works (at least most of the time)?
>> The swizzling is performed early on during the application startup:
>
> If you want to be absolutely sure your swizzling is performed early on during
> application startup, use a +load method instead of a +initialize method.
OK, I've change it to a +load method. We'll see if I no longer receive crash
reports referencing misbehaving PDFPages.
Thanks Greg,
António
-----------------------------------------------------------
And could you keep your heart in wonder
at the daily miracles of your life,
your pain would not seem less wondrous
than your joy.
--Kahlil Gibran
-----------------------------------------------------------
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