error："_OBJC_CLASS_$_MBProgressHUD", referenced from: objc-class-ref in ViewController.o

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)

這裏的錯誤是因爲你的在building phases中沒有引用相關的頭文件，因此，只需要在building phase中添加對應的.m文件就可以了。

或者是缺少相應地框架：

在target-》build phase-》Link binary with libraries中加入相應的框架即可。