http://blog.csdn.net/huayu_huayu/article/details/51781953 （参考链接）
Undefined symbols for architecture armv7:
"_kUTTagClassMIMEType", referenced from:
-[AFStreamingMultipartFormData appendPartWithFileURL:name:error:] in AFURLRequestSerialization.o
"_kUTTagClassFilenameExtension", referenced from:
-[AFStreamingMultipartFormData appendPartWithFileURL:name:error:] in AFURLRequestSerialization.o
"_UTTypeCreatePreferredIdentifierForTag", referenced from:
-[AFStreamingMultipartFormData appendPartWithFileURL:name:error:] in AFURLRequestSerialization.o
"_UTTypeCopyPreferredTagWithClass", referenced from:
-[AFStreamingMultipartFormData appendPartWithFileURL:name:error:] in AFURLRequestSerialization.o
ld: symbol(s) not found for architecture armv7
clang: error: linker command failed with exit code 1 (use -v to see invocation)
解决方法：
这是缺少MobileCoreServices.framework
引入MobileCoreServices.framework即可
