修改 Project --> BuildSetting --》Architectures：
Build Active Architecture Only = YES；
Valid Architectures = arm64 armv7 armv7s armv6;
原文：http://stackoverflow.com/questions/19213782/undefined-symbols-for-architecture-arm64
修改 Project --> BuildSetting --》Architectures：
Build Active Architecture Only = YES；
Valid Architectures = arm64 armv7 armv7s armv6;
原文：http://stackoverflow.com/questions/19213782/undefined-symbols-for-architecture-arm64