This is sample code with ExtenalAccessory Framework in Apple API .
ExternalAccessory framework provides support for communicating with external hardware, which is accessories connected to iOS-based device by the Apple Lightning connector, or connected wirelessly through Bluetooth.
Applications that support external accessories must be sure to configure their Info.plist file correctly. Specifically, you must include the UISupportedExternalAccessoryProtocols key to declare the specific hardware protocols your application supports. For more information about this framework, see (External Accessory Programming Topics).