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)
这里的错误是因为你的在building phases中没有引用相关的头文件,因此,只需要在building phase中添加对应的.m文件就可以了。