How can I set CG_CONTEXT_SHOW_BACKTRACE environmental variable?
You can set an environmental variable via this menu: Product -> Scheme -> Edit Scheme. Under the "Run" item, locate the "Arguments" tab, you'll see "Environmental Variables" in the tab, Add CG_CONTEXT_SHOW_BACKTRACE and set its value to YES.
This problem happen with Xcode 7. In my case i removed the UIViewControllerBasedStatusBarAppearance from Info.plist and the problem solved! See the answer in this post: