I get this error:
Undefined symbols for architecture i386:
"_OBJC_CLASS_$_GameCenterManager", referenced from:
objc-class-ref in BT_viewController.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
My Info:
Ld /Users/Raoul/Library/Developer/Xcode/DerivedData/latintogopro-fbrntyvxhakjwlfaxcckdbvsvcli/Build/Products/Debug-iphonesimulator/LatinToGo.app/LatinToGo normal i386
cd /Users/Raoul/Downloads/latintogopro_v15_iOS
setenv MACOSX_DEPLOYMENT_TARGET 10.6
setenv PATH "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch i386 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.0.sdk -L/Users/Raoul/Library/Developer/Xcode/DerivedData/latintogopro-fbrntyvxhakjwlfaxcckdbvsvcli/Build/Products/Debug-iphonesimulator -L/Users/Raoul/Downloads/latintogopro_v15_iOS/BT_Objects/TwitterOAuth/SAOAuthTwitterEngine -F/Users/Raoul/Library/Developer/Xcode/DerivedData/latintogopro-fbrntyvxhakjwlfaxcckdbvsvcli/Build/Products/Debug-iphonesimulator -F/Users/Raoul/Downloads/latintogopro_v15_iOS/BT_Objects -filelist /Users/Raoul/Library/Developer/Xcode/DerivedData/latintogopro-fbrntyvxhakjwlfaxcckdbvsvcli/Build/Intermediates/latintogopro.build/Debug-iphonesimulator/latintogopro.build/Objects-normal/i386/LatinToGo.LinkFileList -mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -Xlinker -no_implicit_dylibs -D__IPHONE_OS_VERSION_MIN_REQUIRED=50000 -framework Security -framework GameKit -lxml2.2 -framework CoreAudio -framework CoreLocation -framework Foundation -framework SystemConfiguration -weak_framework UIKit -framework MobileCoreServices -framework AVFoundation -weak_framework MessageUI -lOAuth -framework MapKit -weak_framework MediaPlayer -framework CoreGraphics -framework QuartzCore -weak_framework iAd -o /Users/Raoul/Library/Developer/Xcode/DerivedData/latintogopro-fbrntyvxhakjwlfaxcckdbvsvcli/Build/Products/Debug-iphonesimulator/LatinToGo.app/LatinToGo
Go to your project, click on Build phases, Compile sources, Add GameCenterManager.m to the list.
Hope this will help :)
Presumably your code refers to the class called GameCenterManager but your project doesn't link to the framework that defines it.
If this is a built-in framework, then link to that framework: edit the target, in the Summary scroll down to the linked frameworks, press the Plus button to add the framework.
If this is a third-party framework, they should provide instructions for linking to their framework.
来源：https://stackoverflow.com/questions/9660718/xcode-linker-error