Calling method on category included from iPhone static library causes NSInvalidArgumentException

Question

I have created a static library to house some of my code like categories.

I have a category for UIViews in "UIView-Extensions.h" named Extensions.

In this category I have a method called:

- (void)fadeOutWithDelay:(CGFloat)delay duration:(CGFloat)duration;

Calling this method works fine on the simulator on Debug configuration.

However, if try to run the app on the device I get a NSInvalidArgumentException:

[UIView fadeOutWithDelay:duration:]: unrecognized selector sent to instance 0x1912b0
 *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '*** -[UIView fadeOutWithDelay:duration:]: unrecognized selector sent to instance 0x1912b0

It seems for some reason UIView-Extensions.h is not being included in the device builds.

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What I have checked/tried

I did try to include another category for NSString, and had the same issue.

Other files, like whole classes and functions work fine. It is an issue that only happens with categories.

I did a clean all targets, which did not fix the problem.

I checked the static library project, the categories are included in the target's "copy headers" and "compile sources" groups.

The static library is included in the main projects "link binary with library" group.

Another project I have added the static library to works just fine.

I deleted and re-added the static library with no luck

-ObjC linker flag is set

Any ideas?

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nm output

libFJSCodeDebug.a(UIView-Extensions.o):
000004d4 t -[UIView(Extensions) changeColor:withDelay:duration:]
00000000 t -[UIView(Extensions) fadeInWithDelay:duration:]
000000dc t -[UIView(Extensions) fadeOutWithDelay:duration:]
00000abc t -[UIView(Extensions) firstResponder]
000006b0 t -[UIView(Extensions) hasSubviewOfClass:]
00000870 t -[UIView(Extensions) hasSubviewOfClass:thatContainsPoint:]
000005cc t -[UIView(Extensions) rotate:]
000002d8 t -[UIView(Extensions) shrinkToSize:withDelay:duration:]
000001b8 t -[UIView(Extensions) translateToFrame:delay:duration:]
         U _CGAffineTransformRotate
000004a8 t _CGPointMake
         U _CGRectContainsPoint
         U _NSLog
         U _OBJC_CLASS_$_UIColor
         U _OBJC_CLASS_$_UIView
         U ___CFConstantStringClassReference
         U ___addsf3vfp
         U ___divdf3vfp
         U ___divsf3vfp
         U ___extendsfdf2vfp
         U ___muldf3vfp
         U ___truncdfsf2vfp
         U _objc_enumerationMutation
         U _objc_msgSend
         U _objc_msgSend_stret
         U dyld_stub_binding_helper

Answer 1

Unfortunately, due to the what categories work and the dynamic nature of the Objective-C runtime, not everything works well with static libraries. The reason you get this error is that the category implementation in the static library is never actually linked into the executable image because the compiler has no way of knowing that the implementation code will be needed at run-time.

In order to cure this, you can force the linker to copy object files from a static archive for any and all Objective-C Class and Category images. The downside is that your executable will include image code for classes that you may not be using at all. To get the linker to include the category code, add -ObjC to the OTHER_LD_FLAGS build setting in Xcode. Your category implementation will now be copied from the static archive to your executable and you won't get the runtime exception.

Answer 2

The only solution that worked was to include:

"-all_load"

in other linker flags.

I know this isn't the correct method, but it is working for now.

It maybe a OS 3.0 issue since this was the work around for Three20 as well.

Answer 3

In the past I was able to force linkage of the category with -u .objc_category_name_UIView_Extensions, but with the 3.0 dev environment that's broken and the only option seems to be -all_load.

Answer 4

I ran into this problem recently. I was unable to get the -all_load to work, when I noticed that another category I had DID work. I was lazy for this category and included it in with another file.

I eventually created a dummy class (no methods, instance variables) and included the implementation of my categories in the .m file for that dummy class. After doing this my categories started working even after I removed the -all_load flag.

This was on iPhone OS 3.1.3.

This certainly is not the RIGHT way to fix it, but it seemed to work.

Full sample code is on my blog for my (trivial) categories.

Answer 5

I had the same problem with Categories in my static library. In my case, "-all_load" didn't help as it caused loads of build errors (my static library is a wrapper around another private C/C++ lib).

I solved it by a hack suggested at http://iphonedevelopmentexperiences.blogspot.com/2010/03/categories-in-static-library.html which simply involved adding a dummy (empty) class definition to the category files. Using this hack, I kept "-ObjC" but dropped "-all_load" in the application linker settings and it worked fine on the device.

Answer 6

I just spoke to an Apple engineer about this, and this has been addressed in ld with versions >100. This is included in XCode4. He walked me through this and I tried it myself and indeed the category problem is fixed.

Take out "-all_load" and go back to "-ObjC" in your Build Settings with the new linker.

Answer 7

If you are on Xcode 3.2 you can avoid using -all_load and instead use -force_load for just the library in question, which should be slightly more efficient.

This is described in a recently updated Apple Technical QA: http://developer.apple.com/mac/library/qa/qa2006/qa1490.html