to store data that will persist between application instances:

• use one of the methods described here: http://developer.android.com/guide/topics/data/data-storage.html

  e.g. shared preferences, database, etc.

to store key, value data only for an application’s lifetime:

• use onSaveInstanceState and onRestoreInstanceState

  examples:

  • http://stackoverflow.com/questions/151777/how-do-i-save-an-android-applications-state/151940#151940
  • http://www.eigo.co.uk/Managing-State-in-an-Android-Activity.aspx#Store-State-in-State-Bundle

to store object instances for an application’s lifetime:

• use onRetainNonConfigurationInstance: http://www.eigo.co.uk/Managing-State-in-an-Android-Activity.aspx#How-to-Store-Object-Instances

to cache data temporarily:

• use a singleton
  • source: http://developer.android.com/reference/android/app/Application.html
  • note that singletons can be destroyed at any time by the system
• you can instantiate Android’s Application class, but it provides no benefits over creating a singleton; it has no life cycle, and the system can destroy it at any time http://stackoverflow.com/questions/3826905/singletons-vs-application-context-in-android#comment-8239632

to connect to the same database in different activities of the same application:

• open the database connection in each activity’s OnResume method, close it in the OnPause method: http://stackoverflow.com/questions/1556930/sharing-sqlite-database-between-multiple-android-activities/1557465#1557465
  • this is because you can’t have multiple connections to the same database (at least not write connections) due to locking
  • even if it did work, it wouldn’t be wise. opening and closing the database is the best and safest way http://stackoverflow.com/questions/1905846/android-accessing-single-database-from-multiple-activities-in-application/1906047#1906047