GUI Design for Android Apps, Part 2: The Android-Specific GUI
This chapter describes the state transitions of activities and discusses the Context class, intent, and the relationship between applications and activities.
State Transitions of Activities
As mentioned in Chapter 1, the activity is the most important component. Activities have their own state and transition rules, and they are the basis of what you need to understand to write Android applications.
When activities are created or destroyed, they enter or exit the activity stack. And as they do, they transition among four possible states: