Undefined Symbols for Architecture x86_64: (Linker command failed with exit code 1)

when it appearslinker command failed with the exit code 1 (use-v to see invocation) Error Summary, the details are as follows:Undefined Symbols for architecture x86_64:"_objc_class_$_appdelegate", referenced from:Objc-class-ref in MAIN.OLd:symbol (s) not found for architecture x86_64clang:error:linker command failed with exit code 1 (use-v to see invocation)Workaround: Find your project, Buildphases,compile source, and then the fancy hint can not find the class name, here is Appdelegate, so in the Compile Source column, click on the lower left corner of the "+" number, Manually add APPDELEGATE.M, run the program again, perfect solution!As for the appearance of Undefined symbols for architecture armv7: Such an error hint, you can refer to this link to resolve http://blog.csdn.net/hengshujiyi/article/ details/21182813

Undefined Symbols for Architecture x86_64: (Linker command failed with exit code 1)