Undefined symbols for architecture i386或者armv7: “_OBJC_CLASS_$_XXX”

Undefined symbols for architecture i386:

“_OBJC_CLASS_$_XXX”,  referen ced from:

objc-class-ref in XXX

ld: symbol(s) not found for architecture i386

clang: error: linker command failed with exit code 1 (use -v to see invocation)

原文出处：http://blog.sina.com.cn/s/blog_5920503a0100zbda.html