How to sync scroll of two CoordinatorLayout + AppBarLayout

Question

I have an activity with XML.

Something like:

Answer 1

How can I sync scroll of these 2 AppBarLayouts so that the outer appbar collapses either before/after (doesn't matter if it happens before or after) the inside appbar collapses?

Delete that Fragment's CoordinatorLayout and just use RelativeLayout as a root tag (for Fragment)and then do your stuffs with that ViewPager in the MainActivity.

For example, use it inside that CoordinatorLayout like this:

Github example:

https://github.com/TheLittleNaruto/SupportDesignExample

Or perhaps you want to scroll that ViewPager inside the NestedScrollView but, you'll face a problem then use the following code inside it:

app:layout_behavior="@string/appbar_scrolling_view_behavior"

That's pretty much it.

A fragment of the ViewPager has a CoordinatorLayout and AppBarLayout+CollapsingToolbarLayout. XML:

You don't need to use them twice.