问题： 在和Unity交互的过程中，从Unity开发工具打包出来的项目文件，在添加AFNetworking库，运行时报出以下错误：
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)
原因是未添加 MobileCoreServices.framework（此框架定义统一类型标识符 (UTIs)使用的底层类型）
解决：Build Phase ->Link Binary With Libraries()下添加 MobileCoreServices.framework。添加成功后运行程序成功。
