has been modified since the precompiled header… was built

fatal error: file '/Applications/Xcode.app/Contents/Developer/Platforms/iPhoneSimulator.platform/Developer/SDKs/iPhoneSimulator8.1.sdk/System/Library/Frameworks/Foundation.framework/Headers/NSError.h' has been modified since the precompiled header '/Users/username/Library/Developer/Xcode/DerivedData/XXXXX-cxznrhprigvywraxnqppvnynkvxj/Build/Intermediates/PrecompiledHeaders/XXXXX-Prefix-emvrlxfysuvmoxeazxpwhbukltvp/XXXXXX-Prefix.pch.pch' was built

具体的解决方法：

删除/Users/rjxyrjxy/Library/Developer/Xcode/DerivedData/ModuleCache目录下的所有文件

但是如何找到路径呢

这里我来告诉大家一个简单快捷的方法(Library是隐藏文件，不容易找的)

在Finder上点——>前往——>前往文件夹或 Shift + Command + G，会自动弹出让你输入路径，例如：/Users/rjxyrjxy/Library/Developer/Xcode/DerivedData/ModuleCache

会自动找到文件的，删除里面的所有文件就OK了，不过呢，还是报错误的话,你还可以这样做 Project——>Clean ,或 Shift + Command + K