Mark Murphy, founder of CommonsWare, writes a lot.
His most recent books have been focused on second-generation Android app development (Kotlin and the Android Jetpack):
Elements of Android Jetpack, a new introductory book on Android app development, focused on second-generation techniques. Version 0.7 is available, with 846 pages, covering Android Studio 3.5.3 and up through Android 10.
Exploring Android, a series of step-by-step tutorials for building an Android app from scratch. This book is being rewritten to demonstrate using Kotlin and the Jetpack libraries. Version 1.0 is available, with 36 tutorials spanning 576 pages.
Elements of Android Q, to help you deal with the changes introduced by Android 10 (code-named "Q"), such as the changes in external storage access. The final version is available, comprising 96 pages.
Elements of Android Room, to help you incorporate Google's reactive object wrapper around SQLite. Version 0.2 is available, comprising 162 pages.
Elements of Kotlin, a guide to the Kotlin programming language, which is rapidly gaining in popularity for Android app development. Version 0.2 is available, comprising 342 pages.
Elements of Kotlin Coroutines, exploring Kotlin's new first-class reactive programming system. Version 0.1 is available, comprising 170 pages.
In the beginning, Android development was focused on Java and, partially, on the Android Support Library. Mark's earliest books share that focus:
The Busy Coder's Guide to Android Development, the first and largest book on Android app programming
Things Other Than Books
He offers training on Android app development topics, from "starting from scratch" introductory material to advanced areas.
Heck, he even has a blog.
All code in Stack Overflow questions, answers, or comments written by Mark Murphy are hereby licensed under the Apache Software License 2.0, unless otherwise noted where that code appears on Stack Overflow.