In everyday development on Android, you'll find that the core platform and support libraries offer a wide range of widgets and layouts for you to build your application. There are also a wealth of open source and third-party widgets available on the internet. The Android Arsenal website (https://android-arsenal.com/) is a well-cataloged list of APIs available for Android, and it is an excellent starting point when you need some functionality that is not available in the platform or support libraries. Even with this massive wealth of available widgets and libraries, you'll sometimes find yourself wanting a widget that hasn't already been built.
Creating your own widgets on any platform is a sizable undertaking. Widgets need to be able to render themselves to look as native as possible using graphics primitives such as lines, arcs, circles, and polygons. Many Android widgets (such as Button) avoid having to do this using the excellent Drawable class...