Undefined symbols for architecture i386: _OBJC_CLASS_$_SKPSMTPMessage", referenced from: error

错误提示:

Undefined symbols for architecture i386:

"_OBJC_CLASS_$_SKPSMTPMessage", referenced from:
  objc-class-ref in ConfirmController.o

"_kSKPSMTPPartContentTransferEncodingKey", referenced from:
  -[ConfirmController sendEmail] in ConfirmController.o

"_kSKPSMTPPartMessageKey", referenced from:
  -[ConfirmController sendEmail] in ConfirmController.o

"_kSKPSMTPPartContentTypeKey", referenced from:
  -[ConfirmController sendEmail] in ConfirmController.o

ld: symbol(s) not found for architecture i386
collect2: ld returned 1 exit status

原因：编译找不到.m文件
解决方法

TargetSettings -> Build Phases -> Compile Sources -> add your .m class ->Build and Run

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