The app bar is the area that appears at the top of the display when an app is running and can be configured to contain a variety of different items including the status bar, toolbar, tab bar and a flexible space area. Figure 51-1, for example, shows an app bar containing a status bar, toolbar and tab bar:
The flexible space area can be filled by a blank background color, or as shown in Figure 51-2, an image displayed on an ImageView object:
As will be demonstrated in the remainder of this chapter, if the main content area of the activity user interface layout contains scrollable content, the elements of the app bar can be configured to expand and contract as the content on the screen is scrolled.
