Undefined symbols for architecture i386:
"_OBJC_CLASS_$_MBProgressHUD", referenced from:
objc-class-ref in ViewController.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
解决OBJC_CLASS_$_MBProgressHUD无法引用的问题（转载）
原文：http://www.cnblogs.com/ericasun/p/4298306.html