情景：
在项目中导入了一个第三方工具包，后在同一项目的另一个第三方工具包也包含这个包。因为重复，因而我删掉一个。
1， 报错原因：
Undefined symbols for architecture i386: _OBJC_CLASS_$_XXX", referenced from: error
（XXX为出错的类）
2，解决：
TargetSettings -> Build Phases -> Compile Sources -> add your XXX.m class ->Build and Run
参考：
http://stackoverflow.com/questions/6984368/undefined-symbols-for-architecture-i386-objc-class-skpsmtpmessage-referenc
Undefined symbols for architecture i386: _OBJC_CLASS_$_XXX", referenced from: error,布布扣,bubuko.com
Undefined symbols for architecture i386: _OBJC_CLASS_$_XXX", referenced from: error
原文：http://blog.csdn.net/isharestudio/article/details/22719159