CG_CONTEXT_SHOW_BACKTRACE

Oct 19 10:27:05  [2995] <Error>: CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Oct 19 10:27:05  [2995] <Error>: CGContextTranslateCTM: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

Oct 19 10:27:05  [2995] <Error>: CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

iOS9之后,info.plist中View controller-based status bar appearance设置为NO的话,就会报以上警告

使用iOS7以后的方法:

- (UIStatusBarStyle)preferredStatusBarStyle;

- (UIViewController *)childViewControllerForStatusBarStyle;

- (void)setNeedsStatusBarAppearanceUpdate