CG_CONTEXT_SHOW_BACKTRACE

ios 9报警告如下：

CGContextSaveGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

CGContextTranslateCTM: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

CGContextRestoreGState: invalid context 0x0. If you want to see the backtrace, please set CG_CONTEXT_SHOW_BACKTRACE environmental variable.

原因：设置app的状态栏样式的使用使用了旧的方式，在info.plist里面设置了View controller-based status bar appearance为NO

解决方式：删除info.plist中的View controller-based status bar appearance,并将状态栏交给控制器管理