why does android 'revives' crashing apps?

Question

if you have an android app that has more than one Activity, and Activity A starts B, so if Activity b crashes the process is killed but is revived by android OS and starts Activity A again instead of just shutting down the app, why ?

Answer 1

You're complaining that Android will attempt to recover your app's state gracefully after a crash? ;)

This is the result of Android's resource management and the Activity lifecycle at work. Keep in mind that a single task can be composed of a number of Activities that may span several processes or apps. As outlined here: http://android-developers.blogspot.com/2010/04/multitasking-android-way.html Android processes don't shut down "cleanly" in the traditional *nix process sense. Your app's components receive lifecycle events but after a certain point the app can be killed without further warning so that the system may reclaim its resources.

For example, a user might be browsing the web, click a youtube link launching the youtube app, then click a share button to launch their favorite social networking app and post the video link. This is all part of the same task; if the user presses back several times they'll come back to the page in the browser that they started from.

Once you start up the social networking app, the system might decide that it's running low on memory and it's going to kill off the browser's process to free up more. (After all, it's not in front and the user won't notice.) When the user presses the back button to return to the browser Activity it gets restarted and reconstructs the last state where the user left it. At worst the user experiences a short delay while things reinitialize.

But this same sequence of events restoring a previous Activity state can happen even within the same app in the same process. In your scenario, Activity B closed as the result of the crash. So the system does exactly what it always does - it returns to the previous Activity: Activity A. But Activity A's process isn't still around (it crashed!) so the system restarts it and it can reconstruct its previous state.