public abstract class
This is the base class most of the validation Checks that relate to a single view.
CheckCompoundif you like to validate multiple checks as one unit.
Gets the view we are working on.This can be anything that is a child of TextView e.g. EditText, CompoundButton like Checkboxes
Incase of a spinner you return the selected view like so.
Returns: the View from which to get value to isValid and also on which to set error by invoking view.setError()