为什么我会收到Apple Mach-O链接器（ID）错误？

Question

我知道这个问题已被多次询问过，但每个答案似乎都有所不同。我已经构建了我的项目并尝试运行它，但是我收到了这个错误：

Ld "/Users/******/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator/Cypher Bot.app/Cypher Bot" normal i386
cd "/Users/******/Xcode/iOS/Cypher Bot/Universal/Cypher Bot/Cypher Bot"
setenv MACOSX_DEPLOYMENT_TARGET 10.6
setenv PATH "/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin:/Developer/usr/bin:/usr/bin:/bin:/usr/sbin:/sbin"
/Developer/Platforms/iPhoneSimulator.platform/Developer/usr/bin/clang -arch i386 -isysroot /Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator5.0.sdk -L/Users/********/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator -F/Users/**********/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator -filelist "/Users/*******/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Intermediates/Cypher Bot.build/Debug-iphonesimulator/Cypher Bot.build/Objects-normal/i386/Cypher Bot.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 Security -framework UIKit -framework Foundation -framework CoreGraphics -framework CoreData -o "/Users/********/Library/Developer/Xcode/DerivedData/Cypher_Bot-dxylepzskcnrtybprtuaotmycjjo/Build/Products/Debug-iphonesimulator/Cypher Bot.app/Cypher Bot"

Undefined symbols for architecture i386:
  "_OBJC_CLASS_$_MFMailComposeViewController", referenced from:
  objc-class-ref in CryptoMainViewController.o
ld: symbol(s) not found for architecture i386
clang: error: linker command failed with exit code 1 (use -v to see invocation)

我也在上面的信息下面看到了这一点：

这是什么意思？我该怎么做才能解决它？

Answer 1

错误意味着链接器无法找到MFMailComposeViewController的类定义。该类在MessageUI框架中定义。您是否已将MessageUI框架添加到目标中？如果您不知道如何操作，请阅读：How to "add existing frameworks" in Xcode 4?