Consider the following Coordinator+AppBar+MotionLayout and its MotionScene from Google's demo. This creates a MotionLayout that sync's its Transition progress when the user is scrolling.
Video Preview: https://i.imgur.com/1MnPB8R.mp4
However, I would like to do this in programmatically in Kotlin. Here are my failed attempts.
val motion = findViewById<MotionLayout>(R.id.constraintToolbar)
motion.transitionToState(R.id.end)
The above would cause the MotionLayout to animate, but would immediately blink back to the start state once finished. The AppBarLayout also does not change height.
val appbar = findViewById<AppBarLayout>(R.id.app_bar)
val scrollable = findViewById<NestedScrollView>(R.id.scrollable)
val s = if(motion.progress==0F) appbar.totalScrollRange else 0
scrollable.smoothScrollTo(0, s)
The above scrolls the NestedScrollView, but the AppBarLayout and MotionLayout does not receive the scroll events.
val s = if(motion.progress==0F)-appbar.totalScrollRange else 0
val appbar = findViewById<AppBarLayout>(R.id.app_bar)
appbar.scrollTo(0,s)
appbar.offsetTopAndBottom(s)
The above shifts the AppBarLayout, breaking the layout completely.
How do you trigger this scroll programmatically?
If there's only 2 states, you should try setExpanded()
val e = motion.progress != 0F
appbar.setExpanded(e, true)