Android Material Design - How to change background color of Toolbar after CollapsingToolbarLayout is collapsed

Question

After the user scrolls down the screen, the image in the CollapsingToolbarLayout disappears and is left with a toolbar with the back button, content title,

Answer 1

You can use an AppBarLayout's offset listener and change the CollapsingTollbar attributes according to the desired behavior.

appBarLayout.addOnOffsetChangedListener { _, verticalOffSet ->
            if (Math.abs(verticalOffSet) == appBarLayout.totalScrollRange) {
                //Collapsed
                toolBar.setBackgroundDrawable(ContextCompat.getDrawable(this,
                        R.drawable.last_revolut_gradient))
            } else {
                //Expanded
                toolBar.setBackgroundColor(ContextCompat.getColor(this,
                        android.R.color.transparent))
            }
        }