Why is onDestroy always called when returning to parent activity?

Question

I have a very simple app based on the Building Your First App tutorial. There are two activities: MainActivity invokes DisplayMessageActivity thro

Answer 1

Adding launchMode in Manifest changes launch mode every time, even it is not launched by child activity. There are other ways to launch existed instance.

1.override onOptionsItemSelected(item: MenuItem)

override fun onOptionsItemSelected(item: MenuItem): Boolean {
   return when (item.itemId) {
        android.R.id.home -> {
            // Respond to the action bar's Up/Home button
            val upIntent: Intent? = NavUtils.getParentActivityIntent(this)
            when {
                upIntent == null -> throw IllegalStateException("No Parent Activity Intent")
                else -> {
                    //add launch flag here
                    upIntent.flags=Intent.FLAG_ACTIVITY_CLEAR_TOP
                    NavUtils.navigateUpTo(this, upIntent)
                }
            }
            true
        }
        else -> super.onOptionsItemSelected(item)
    }
}

2. 2nd solution looks like a bug. Set "android:parentActivityName" to activity which is not existed in current task stack. Android will behavior like "BACK" button. It launches the top instance instead of launching parent activity. Document mentions "NavUtils.shouldUpRecreateTask" can recognize if parent activity existed in current task. But it doesn't work in my test. Navigate up with a new back stack

Answer 2

Thanks to Greg Giacovelli's comments, I found the answer here. The solution was to set android:launchMode="singleTop" to the parent activity.

I still can't understand why such basic information is so unknown and hard to find!