There are so many things to learn when developing mobile app development, if you want to learn everything, you will have to spend your whole life. No work will be done. Speaking of Android. More like layouts, fragments, networks, notifications, services, locations, maps, databases, images, rest. So learn everything?
Not everything in a project. Since everything does not take place in one project, so learning everything does not make sense. To learn it will be a lot of time to waste. Know what you need to learn, You can take an idea about what works, or take a float-based knowledge.
To know what to learn, first of all must have basic knowledge. For example, there must be an understanding of Java programming for Android. Then you have to know how to create a simple android app. In addition to creating a simple app, you need to know what kind of app you want to create, a clear idea about.