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?
> 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.
--
Greg Parker gpar...@apple.com Runtime Wrangler
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