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Android Developer Fundamentals

Resources

Unit 1: Get started

Lesson 1: Build your first app

By convention, log tags are defined as constants for the Activity:

private static final String LOG_TAG = MainActivity.class.getSimpleName();

Log.d(LOG_TAG, "Hello World");

Lesson 2: Activities and intents

Lifecycle and state

  • Start of application
    • onCreate
    • onStart
    • onResume
  • Rotation of application and re-rotation
    • onPause
    • onStop
    • onDestroy
    • onCreate
    • onStart
    • onResume
  • Background or sleeping
    • onPause
    • onStop
  • Forground or wakeup
    • onRestart
    • onStart
    • onResume
  • Kill
    • onPause
    • onStop
    • onDestroy
  • Intent to secondActivity from MainActivity
    • MainActivity : onPause
    • SecondActivity : onCreate
    • SecondActivity : onStart
    • SecondActivity : onResume
    • MainActivity : onStop
  • Back with back button from SecondActivity to MainActivity
    • SecondActivity : onPause
    • MainActivity : onDestroy
    • MainActivity : onCreate
    • MainActivity : onStart
    • MainActivity : onResume
    • SecondActivity : onStop
    • SecondActivity : onDestroy
  • Back with the narrow from SecondActivity to MainActivity
    • SecondActivity : onPause
    • MainActivity : onRestart
    • MainActivity : onStart
    • MainActivity : onResume
    • SecondActivity : onStop
    • SecondActivity : onDestroy

To keep from losing data in an Activity when it is unexpectedly destroyed and recreated, you need to implement the onSaveInstanceState() method. The system calls this method on your Activity (between onPause() and onStop()) when there is a possibility the Activity may be destroyed and recreated.