Order of Android Activity lifecycle events

I noticed some variation between devices so I tested various user actions on various devices and recorded the Android Activity lifecycle methods (e.g. onResume, onPause, onCreate, onStop) that got called. My results are below.

[Why? I want to detect whether the user is leaving the app or just transitioning from one activity to another. See my next blog posts Detecting whether an Android app is stopping (or starting) and Code for detecting when you leave an Android app for how to do it.]

Press the home button

• Ensure the app process is stopped.
• Start the app. It starts an Activity.
• Start recording events.
• Press “home” on the device.

onSaveInstanceState
onPause
onStop
  

onPause
onSaveInstanceState
onStop
  

When home was pressed, onPause and onStop were called in that order, and onSaveInstanceState was always called before onStop. The app was still running after the test.

Note that onSaveInstanceState can happen either before or after onPause.

This is consistent with the information given on the Android Activity API docs:

Starting with Honeycomb, an application is not in the killable state until its onStop() has returned. This impacts when onSaveInstanceState(Bundle) may be called (it may be safely called after onPause() and allows and application to safely wait until onStop() to save persistent state.

Press the home button in a second activity

• Ensure the app process is stopped.
• Start the app. It starts Activity1.
• Press a button in the activity that launches Activity2.
• Start recording events.
• Press “home” on the device.

Results are identical to “Press the home button” above, with Activity2 receiving all the calls, and Activity1 not receiving any.

Press the back button to exit

• Ensure the app process is stopped.
• Start the app. It starts an Activity.
• Start recording events.
• Press “back” on the device.

onPause
onStop
onDestroy
  

When back was pressed, onPause, onStop and onDestroy were called. The app process was still running after the test.

onSaveInstanceState was not called, because there is no current state to resume – when you re-enter you will be back at the beginning.

Start the app

• Ensure the app process is stopped.
• Start recording events.
• Start the app.

onCreate
onStart
onResume
  

When the app was started, onCreate, onStart and onResume were called in that order.

Turn off with the power button

• Start the app.
• Start recording events.
• Press the power button (turn off).

onSaveInstanceState
onPause
  

onPause
onSaveInstanceState
onStop

When the phone was suspended, onSaveInstanceState and onPause were called in different orders, and onStop was called in some cases.

Turn on with the power button

• Start the app.
• Press the power button (turn off).
• Start recording events.
• Press the power button (turn on).
• Unlock the device.

onResume
  

onRestart
onStart
onResume
  

When the phone was resumed, onResume was always called, and onRestart and onStart were sometimes called.

Restart the app after pressing home

• Ensure the app process is stopped.
• Start the app.
• Press “home” on the device.
• Start recording events.
• Start the app.

onRestart
onStart
onResume
  

When the app was restarted after pressing home, onCreate was not called, but onRestart, onStart and onResume were (in that order).

Restart the app after pressing back

• Ensure the app process is stopped.
• Start the app.
• Press “back” on the device.
• Start recording events.
• Start the app.

onCreate
onStart
onResume
  

When the app was restarted after pressing back, onRestart was not called, but onCreate, onStart and onResume were (in that order).

This is consistent with the idea that pressing back effectively ends the app, but pressing home effectively pauses it.

Launch a second activity

• Ensure the app process is stopped.
• Start the app. It starts Activity1.
• Start recording events.
• Press a button in the activity that launches Activity2.

Activity1.onSaveInstanceState
Activity1.onPause
Activity2.onCreate
Activity2.onStart
Activity2.onResume
Activity1.onStop
  

Activity1.onPause
Activity2.onCreate
Activity2.onStart
Activity2.onResume
Activity1.onSaveInstanceState
Activity1.onStop
  

The later version of Android called onSaveInstanceState much later in the process. This is consistent with the documentation for the Activity Lifecycle.

In both cases Activity1’s onPause was called before any methods were called on Activity2.

In both cases Activity1’s onStop was called after all methods were called on Activity2.

Activity2’s methods were called just as if it were the starting activity of a freshly-launched app (see “Start the app” above).

Activity1’s methods were called just as if the home button had been pressed.

Launch an external activity

• Ensure the app process is stopped.
• Start the app. It starts an Activity.
• Start recording events (in our activity only).
• Press a button in the activity that launches the Android web browser.

Results are identical to “Press the home button” above.

Go back from one activity to another

• Ensure the app process is stopped.
• Start the app. It starts Activity1.
• Press a button in the activity that launches Activity2.
• Start recording events.
• Press “back” on the device.

Activity2.onPause
Activity1.onRestart
Activity1.onStart
Activity1.onResume
Activity2.onStop
Activity2.onDestroy
  

Activity2 sees the same calls as in “Press the back button to exit” (i.e. it is destroyed).

Activity1 see the same calls as in “Restart the app after pressing home” (i.e. it is resumed).

Go back from an external activity to ours

• Ensure the app process is stopped.
• Start the app. It starts an Activity.
• Press a button in the activity that launches the Android web browser.
• Start recording events (in our activity only).
• Press “back” on the device.

Results are identical to “Restart the app after pressing home” above.

See my next blog post for how to detect whether we are leaving the app, or just transitioning between activities: Detecting whether an Android app is stopping (or starting).