212 CHAPTER 6: Android Screen Design: Writing to the Display Using Activity and View
and ViewGroup subclasses are concerned, Android has generously written all of the subclasses for
you; all you have to do is to “include” them in your application code by using an import statement,
and of course you have to implement their features correctly.
You learned about the relationship between the Activity class, the View class, and the ViewGroup
class, and how these are used together to get your application UI design and content onto the
device display screen. Then you used the Galaxy class you created in the previous chapter to create
a Galaxy object to use in this chapter, where we create a Galaxy Information Screen UI design.
Then you learned about the LinearLayout class and how to create a UI design using this simple UI
layout container designed for designing row-oriented or column-oriented UI layouts. You learned
about the Project ➤ Clean work process in case you ever start up your application to a project filled
with errors that you did not create, and how to go about restarting the IDE and/or using the Clean
command to make sure ADT sees the Java SDK, or JDK, and the java.lang.Object class.
You learned how to reference digital image assets in your UI layout containers, how to use
transparency, and how to nest LinearLayouts to create more complex UI layout designs. You also
learned how to modularize your Java code by writing your own custom methods, as well as how to
call those methods from inside other methods. You learned a couple different ways to declare and
instantiate objects so that code inside all of your class methods could see them.
In Chapter 7, you will start to learn about how Android handles Events, uses Intent objects, and
Menu objects by using the Android Menu subclasses, and all about how to make UI designs and
Menu systems interactive, by using Event Handlers and Intent objects.