GreenDAO is an Object-Relational Mapping library to help developers use SQLite databases for persistent local storage.
The general idea behind Dependency Injection is that you design your application around loosely coupled components while adhering to the Dependency Inversion Principle. By not depending on concrete implementations, allows to design highly flexible systems.
Aspnet core is built with Dependency Injection as one of its key core concepts. It introduces one conforming container abstraction so you can replace the builtin one with a third-party container of your choice.