How do mobile app developers customize apps for different smartphones on the same operating system?

Question

Android

Hello! Let's say there is an operating system for Android smartphones (there are a dozen versions of Android) that runs on a large number of different smartphones. How is a mobile application customized for all versions of android and for all devices? Or do they simply take those versions of the operating system that are relevant at the time the application was created? And with a large number of different smartphones, how do they solve the problem?

Answer 1

specifically for android, here is
developer.android.com/training/basics/supporting-d...
developer.android.com/training/basics/supporting-d...
in short,
to support different screens, graphics are created in several resolutions and put in folders with special suffix xhdpi, hdpi, mdpi, ldpi. layouts for tablets are placed in the layout-large folder, for landscape orientation in layout-land (all this is not necessary, if they are absent, default resources are used)
to implement features of later versions of the OS, the Android Support Library (actionbar, fragments, etc.) e.)
such a selection will not save, both android 2.3 and 4 are widely used. *

Answer 2

Usually they have a dozen or two devices with different OS versions and characteristics.