'invalid context 0x0' after Migration to iOS 9
问题 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