Ios 无法清除Xcode 6中的用户默认值

尝试使用以下代码清除UserDefaults（持久性数据）时：

    var mainBundle:NSBundle = NSBundle.mainBundle()
    var appDomain:NSString = mainBundle.bundleIdentifier!
    userDefaults.removePersistentDomainForName(appDomain)

第三条语句不会编译，但会生成Apple Mach-O链接器错误：

Ld /Users/Alexander/Library/Developer/Xcode/DerivedData/AD62-bxdlketythywrzhfutzehevdbmyx/Build/Products/Debug-iphonesimulator/AD62.app/AD62 normal x86_64
    cd /Users/Alexander/Desktop/AD62
    export IPHONEOS_DEPLOYMENT_TARGET=8.0
    export 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"
...    
Undefined symbols for architecture x86_64:
  "__TFSs26_forceBridgeFromObjectiveCU__FTPSs9AnyObject_MQ__Q_", referenced from:
      __TFC4AD6226ProfileTableViewController13viewDidAppearfS0_FSbT_ in ProfileTableViewController.o
ld: symbol(s) not found for architecture x86_64
clang: error: linker command failed with exit code 1 (use -v to see invocation)

非常感谢您的帮助。

此功能：

var mainBundle:NSBundle = NSBundle.mainBundle()
userDefaults.removePersistentDomainForName(mainBundle.bundleIdentifier!)

我看不出有多大区别，但事实就是这样