Google developed Android in China's official website
https://developer.android.google.cn/guide
There are many materials under development, there are explanations, and examples. Categories is clear.
in
https://developer.android.google.cn/samples
There are many examples below, but some kotlin, I only use java. Some examples seem obsolete.
There are examples of android's official repository on github. From the top link to get there.
Use android studio's new features, you can build some examples of interface.
On several major components used in the current development activity, intent; the use of very simple basic service, provider; do not use broadcast. Bundling of resources, and placeholders, nor how to use, in order to save. About asynchronous calls Android api, there is little understanding, there is no use.
Two months before the transplant from android support to androidx, there is a document library, and the development of more convenient.
recyclerView, and viewpager2 + tablayout + fragment + viewmodel, quite interesting.
Their android development, application of the idea mvc structure, can be passed via intent objects packaged in the activity, the use of android automatically parcel,. Event interface components different response action can be packaged as a method, process interface interaction, then call handler inside methods, processes application logic. Components related to different events may call the same action method for operating the same interface, or a different method of action of different interface operation; call handler with one or more methods, processes application logic in the action of these methods. Such Development Authority and some simple modifications.
Database Framework room android, and read the introduction to explain, not yet used.