Xcode：我刚遇到一个Apple Mach-O Linker（Id）错误，不知道为什么

Question

I'm new to iOS Development, I'm using the latest version of Xcode and just got an error that said Apple Mach-O Linker (Id) Error exit code 1 and I haven't got a clue why. I think this is relevant but I'm not sure what it means:

ld: duplicate symbol _OBJC_CLASS_$_Timing1ViewController in /Users/tomkenning/Library/Developer/Xcode/DerivedData/EggTimer-ciznfdheqrtybuavrtbbcxfywyyw/Build/Intermediates/EggTimer.build/Debug-iphonesimulator/EggTimer.build/Objects-normal/i386/Mediumhb.o and /Users/tomkenning/Library/Developer/Xcode/DerivedData/EggTimer-ciznfdheqrtybuavrtbbcxfywyyw/Build/Intermediates/EggTimer.build/Debug-iphonesimulator/EggTimer.build/Objects-normal/i386/Timing1ViewController.o for architecture i386

All I've done recently is initialise and set some integer values in a .m file and then link to them from .h file from another ViewController, using #import "suchandsuch.m", there's been no errors in the code, but is that not allowed?

Thanks in advance for any help you can offer!

Answer 1

Don't do this:

#import "suchandsuch.m" 

Do this:

#import "suchandsuch.h" 

You are probably compiling suchandsuch.m , which defines the class Timing1ViewController , normally (by including suchandsuch.m in your target's list of files to build). Then your #import "suchandsuch.m" causes that same code to be inserted into a different source file, which is compiled as well. The result: two different source files try to define Timing1ViewController .

To do your constants the right way -- by declaring them extern in suchandsuch.h and defining them in suchandsuch.m -- see this answer .

Answer 2

You probably have two Timing1ViewController classes with the same name. If you don't try to Product -> Clean and build again.