The iOS SDK API for New Relic Mobile requires modification of your project‘s prefix header. If your project does not have one, follow these steps to add it.
From your Xcode menu, select File > New > File...
From iOS template options, select Other > PCH file.
Name the file <target_name>-Prefix.pch, and then select Create.
From your target’s Build settings, select All, and then add the following to the Prefix Header field:
$(SRCROOT)/<target_name>-Prefix.pch
Adding a prefix header to an iOS project
原文：http://www.cnblogs.com/qike/p/5208887.html