Question

I have a tab host control that is loading tabs using fragments.

Each time a tab is switched it detaches the old fragment and attaches the new fragment.

I noticed that the OnCreateView method is called during this process, and that a lot of my state is getting lost since it recreates the view each time. However I noticed that some view state such as the value of edit text is being maintained across detach/attach.

I’m wondering how Android is automagically restoring state when the view is being completely destroyed and recreated as a new view. The value of the Bundle savedInstanceState is always null when I am just switching tabs. Bundle savedInstanceState only becomes populated when I do something like rotating the screen.

as far as I can tell this restoring of state is taking place just before the fragment onStart method is called.

Answer 1

When attaching and detaching fragments only the views are destroyed, the fragment instance remains the same.

The fragment manager restores the states of views that have ids, and the savedInstanceState is null.

In case of rotation, the fragments are probably recreated by you somewhere else (in activity’s onCreate()?).