Some Android devices offer a slide-out keyboard that triggers rotating the screen from portrait to landscape orientation. Other devices use accelerometers to determine when the screen rotates. As a result, it is reasonable to assume that switching from portrait to landscape orientation and back again may be something that users of your application will want to do.
As this chapter describes, Android has a number of ways for you to handle screen rotation so that your application can properly handle either orientation. Keep in mind, though, that these facilities only help you to detect and manage the rotation process—you still must make sure your layouts and fragments look decent in each orientation.