我在我现在正在处理的项目中添加了一个名为 RootViewController 的现有类。该项目第一次编译，但我第二次尝试运行它时弹出 mach-o-linker 错误。我没有为此更改任何代码，所以我真的不知道出了什么问题。我知道这个错误通常是因为缺少框架，但我很确定我包含了我需要的所有框架。
这是日志：
Ld /Users/myusername/Library/Developer/Xcode/DerivedData/coredataproject-dhlbawbtzwdgohaczdnalonzhnhs/Build/Products/Debug-iphonesimulator/coredataproject.app/coredataproject normal i386
cd /Users/myusername/Desktop/coredataproject
setenv MACOSX_DEPLOYMENT_TARGET 10.6
setenv PATH "/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Applications/Xcode.app/Contents/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/clang -arch i386 -isysroot /Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.0.sdk -L/Users/myusername/Library/Developer/Xcode/DerivedData/coredataproject-dhlbawbtzwdgohaczdnalonzhnhs/Build/Products/Debug-iphonesimulator -F/Users/myusername/Library/Developer/Xcode/DerivedData/coredataproject-dhlbawbtzwdgohaczdnalonzhnhs/Build/Products/Debug-iphonesimulator -filelist /Users/myusername/Library/Developer/Xcode/DerivedData/coredataproject-dhlbawbtzwdgohaczdnalonzhnhs/Build/Intermediates/coredataproject.build/Debug-iphonesimulator/coredataproject.build/Objects-normal/i386/coredataproject.LinkFileList -mmacosx-version-min=10.6 -Xlinker -objc_abi_version -Xlinker 2 -fobjc-arc -Xlinker -no_implicit_dylibs -D__IPHONE_OS_VERSION_MIN_REQUIRED=50000 -framework UIKit -framework Foundation -framework CoreGraphics -framework CoreData -framework CoreLocation -framework MapKit -o /Users/myusername/Library/Developer/Xcode/DerivedData/coredataproject-dhlbawbtzwdgohaczdnalonzhnhs/Build/Products/Debug-iphonesimulator/coredataproject.app/coredataproject
Undefined symbols for architecture i386:
"_OBJC_CLASS_$_RootViewController", referenced from:
objc-class-ref in FirstViewController.o
objc-class-ref in AppDelegate.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)
我已经搜索了几个小时试图找到丢失的链接或参考，但我没有发现任何问题。任何帮助将不胜感激。