Android developer reference:

Kotlin bootcamp Google:

https://www.udacity.com/course/kotlin...

For Android fundamentals:

https://developer.android.com/docs

https://www.udacity.com/course/androi...

For UI:

https://developer.android.com/design


For data persistence and networking:

https://codelabs.developers.google.com/

https://developer.android.com/guide


Blogs:

  / androiddevelopers  

https://dev.to/search?q=Android%20

Books mentioned:

1. "Head First Java" by Kathy Sierra and Bert Bates
2. "Kotlin Programming: The Big Nerd Ranch Guide" by Josh Skeen and David Greenhalgh
3. "Android Programming: The Big Nerd Ranch Guide" by Bill Phillips, Chris Stewart, and Kristin Marsicano
4. "Android User Interface Design: Implementing Material Design for Developers" by Ian G. Clifton
5. "Android Programming: Pushing the Limits" by Erik Hellman
6. "Effective Java" by Joshua Bloch
7. "Android Apprentice" by the raywenderlich.com Team