学习NSNotification时遇到了这个问题，错误日志如下：
2015-08-28 17:47:24.617 NSNotificationDemo[7158:786614] *** Terminating app due to uncaught exception 'NSInternalInconsistencyException', reason: 'Could not load NIB in bundle: 'NSBundle </private/var/mobile/Containers/Bundle/Application/18D95FA1-2AA9-48B8-9528-4FD9B9B65B75/NSNotificationDemo.app> (loaded)' with name 'ViewController'' *** First throw call stack: (0x287910d7 0x36c23c77 0x2879101d 0x2c1c32a9 0x2c0da987 0x2bf0e6dd 0x2bdf2349 0x2bdf22cd 0x2bdf83f7 0x2bdf5d6f 0x2be60e91 0xebad9 0x2be5dc85 0x2c05426b 0x2c05690f 0x2c0615e9 0x2c0550c7 0x2f265ec1 0x28757035 0x287562f9 0x28754e53 0x286a06d1 0x286a04e3 0x2be57867 0x2be52445 0xebc3d 0x371f1aaf) libc++abi.dylib: terminating with uncaught exception of type NSException2015-08-
