3.3.2. Activity Lifecycle Methods

Throughout its life, an Activity can be in one of several states—active (i.e., running), paused or stopped. The Activity transitions between these states in response to various events:

• An active Activity is visible on the screen and “has the focus”—that is, it’s in the foreground. This is the Activity the user is interacting with.

• A paused Activity is visible on the screen but does not have the focus—such as when an alert dialog is displayed.

• A stopped activity is not visible on the screen and is likely to be killed by the system when its memory is needed. An Activity is stopped when another Activity becomes active.

As an Activity transitions among these states, the Android runtime calls various Activity lifecycle methods—all of which are defined in the Activity class

You’ll override the onCreate method in every activity. This method is called by the Android runtime when an Activity is starting—that is, when its GUI is about to be displayed so that the user can interact with the Activity. Other lifecycle methods include onStart, onPause, onRestart, onResume, onStop and onDestroy. We’ll discuss most of these in later chapters. Each activity lifecycle method you override must call the superclass’s version; otherwise, an exception will occur. This is required because each lifecycle method in superclass Activity contains code that must execute in addition to the code you define in your overridden lifecycle methods.