I've migrated the app to iOS 9, and it works as usually, but there three log messages:
<Error>: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
<Error>: CGContextTranslateCTM: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
<Error>: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.
Maybe helps that the next message from Crashlytics is:
[Crashlytics:Crash] Warning: iOS 9 workaround for binary image loading issue in place.
Does anybody know how to fix it?
This happens when there is a definition of UIViewControllerBasedStatusBarAppearance with false in info.plist.
If you don't need this you can set the key <key>UIViewControllerBasedStatusBarAppearance</key> to true in the file manually or change View controller-based status bar appearance option from Info to YES.
Also, I saw some posts that state there is no problem with this. As far as I know there's no way to set UIViewControllerBasedStatusBarAppearance from code, so I guess we'll have to wait until Apple will fix this issue. You can find more here.
Later Edit: It seems that iOS 9.1 solves this encountered errors. From last stable Xcode, running on iOS 9.1 result in no errors, while 9.0 still has the problems above.
Apple has stated you can safely ignore these messages ': CGContextSaveGState: invalid context 0x0. "
Check the various Apple dev forums or support areas.
来源：https://stackoverflow.com/questions/32540095/invalid-context-0x0-after-migration-to-ios-9