Public static variables and Android activity life cycle management

by

If the process is killed then all static variables will be reinitialized to their default values.

So whatever value you have set in Activity A will not persist

Good explanation can be viewed here from 2:50
http://www.infoq.com/presentations/Android-Design

Here are some instructions for those who want to test this issue manually:
Create android v.4 emulator, then go to settings -> developer settings -> disable background tasks.
Then create sample android project with 2 activities,
declare static variable in activity A, initialize it in onCreate() method.
Place a button in activity A that starts activity B.
In Activity B’s onCreate() method print the value of A.staticVar to logcat.

Launch the project – activity A appears. Hit the button – activity B appears, value of static variable is printed to logcat. Press the home button and launch any other program – your sample project process will be killed (because you have disabled background processes).
Now long-press on home button – you will see the list of recently launched programs. Select your sample project – OS will try to recover your project’s activities back-stack and recreate last running activity B. But at this step program will crash with NullPointerException because A.staticVar will be null, and we are trying to print it to logcat.

More Related Contents:

  1. Creating new Android (Java ) file in Existing Android package [closed]
  2. Start another activity with button
  3. How to pass an object from one activity to another on Android
  4. Maximum length of Intent putExtra method? (Force close)
  5. Finish all previous activities
  6. Sending arrays with Intent.putExtra
  7. How to use interface to communicate between two activities
  8. How to set background color of an Activity to white programmatically?
  9. Android – Activity Constructor vs onCreate
  10. How to start Activity in adapter?
  11. Android Studio cannot resolve symbol but code executes correctly
  12. Android Unable to instantiate activity: Didn’t find class on path
  13. android.app.Application cannot be cast to android.app.Activity
  14. How can I start a new android activity using class name in a string?
  15. How to resume Android Activity programmatically from background
  16. DeadObjectException on android app
  17. What is the correct order of calling superclass methods in onPause, onStop and onDestroy methods? and Why?
  18. Issue: Passing large data to second Activity
  19. Android Call a method from another class
  20. Android: Unable to find explicit activity class… startActivity from a PreferenceActivity
  21. How to exit an Android app programmatically?
  22. How to navigate from one screen to another screen
  23. What’s the difference between this and Activity.this
  24. Lifetime of a static variable in Android
  25. how to programatically theme an activity to be like a dialog?
  26. Android – Dynamically Get the Current Activity in Foreground
  27. IllegalArgumentException: Unknown URL content:// CONTENT
  28. Android: Navigation-Drawer on all activities
  29. Passing ArrayList of string arrays from one activity to another in android
  30. Using the camera activity in Android

Leave a Comment