Lib uses qr-mobile vision library https://github.com/rmtmckenzie/flutter_qr_mobile_vision. It has two screens. First consists of appBar, bottomBar and camera view to read codes. If the code processed is not correct there is an option to enter code manually on the second screen.
Example video:
To start you need to have flutter installed. To work with Android Studio Import the project into it and run main.dart from lib folder.
For help getting started with Flutter, view
online documentation, which offers tutorials,
samples, guidance on mobile development, and a full API reference.