Android View onSaveInstanceState not called

The easy answer : it's because I was not setting id to my view (custom or not). Android didn't manage the onSaveInstanceState/onRestoreInstanceState if no id is set to the view.

So as my customView was extending base View, with not extra property, setting an ID to the view solved the issue and so onSaveInstanceState/onRestoreInstanceState are called as it should.

So to summary, use one of this approach :

from XML

<ScrollView
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    ...
    android:id="@+id/scrollView">
</ScrollView>

OR from Java

yourCustomView.setId(R.id.myCustomView);

is last case, you add static id to res/values/ids.xml <item name="myCustomView" type="id"/>

Saving State by Default

We now have everything in place for our view to save and restore its state. However, this will not happen by default. If you want instances of your view to save state automatically, you can add this line to the init method:

setSaveEnabled(true);

Whether or not to do this is up to you. Even if your view does not save state by default, users of the view can always enable saving state by calling setSaveEnabled(true), or by specifying android:saveEnabled=“true” in the layout xml.