Android Basics - Introduction to Activities and Lifecycle

Overview

• New series focused on core Android concepts for native development.
• Aimed at both beginners and those looking to deepen their Android knowledge.
• Assumes familiarity with Kotlin.
• UI building not covered here – check Jetpack Compose playlist for that.

Topics Not Covered

• Topics that are outdated due to Jetpack Compose (e.g., Fragments).

Activities

• Definition: A container for one or multiple screens in an app.
• Role: Unit of interaction with the user; not just a screen container.
• Entry Point: Activities serve as entry points (e.g., when a user clicks a link in another app).

Evolution of Activities

• Past: One activity per screen.
• Transition: Use of Fragments to bundle related screens.
• Present (Jetpack Compose): Typically one activity for the whole app.

Activity Lifecycle

• Lifecycle States:

  • Created: onCreate function initializes variables and UI content.
  • Started: onStart makes the activity visible.
  • Resumed: onResume allows user interaction.
  • Paused: onPause is called when another UI component comes to the foreground.
  • Stopped: onStop when the activity is no longer visible.
  • Destroyed: onDestroy frees all resources.

• Lifecycle Diagram: Complex at first glance, but logical once understood.

Detailed Lifecycle Explanation

• onCreate: Initialization phase; set up views and variables.
• onStart: Activity becomes visible like a theater curtain opening.
• onResume: Activity is in the foreground and interactive.
• onPause: Activity still in memory, but not in focus (e.g., dialog displayed).
• onStop: Activity not visible; system may reclaim resources.
• onRestart: Called when returning to a stopped activity.
• onDestroy: Final cleaning when activity finishes or system needs resources.

Special Cases

• Configuration Changes: Trigger lifecycle restart (e.g., screen rotation, language switch).
• System Behavior: onStop and onDestroy may not always be called.

Practical Code Explanation

• Example showing lifecycle functions overridden in code.
• Using logs to track lifecycle state transitions.

Key Takeaways

• Use onPause for critical data saving as onStop/onDestroy might not be reliably called.
• Lifecycle understanding is crucial for effective Android app management.

Conclusion

• Regular updates with new videos every Wednesday and Sunday.
• Encouragement to subscribe for continued learning.