Zina - checkpoint 4

In this chapter, we are going to learn more about UI elements and how to make them responsive and dynamic. Firstly, selectors enable us to specify a different drawable to each state of the View to which it has been assigned. Most native Android Views use State List Drawables, including the image used on Buttons, and the background used for standard List View items.
Secondly, there are situations where you have to create your own shape. For that Android provides it’s own solution by declaring it in XML files.
9-patch images make it easy to support different screen sizes and their structure allows them to stretch accross the specified space and still keep their shape nice and smooth.