Android CollapsingToolbarLayout collapse Listener

Question

I am using CollapsingToolBarLayout alongside with AppBarLayout and CoordinatorLayout, and they are working Fine altogether. I set my <

Answer 1

Here is the solution in Kotlin:

abstract class AppBarStateChangeListener : OnOffsetChangedListener {
    enum class State {
        EXPANDED, COLLAPSED, IDLE
    }

    private var mCurrentState =
        State.IDLE

    override fun onOffsetChanged(appBarLayout: AppBarLayout, i: Int) {
        mCurrentState = if (i == 0) {
            if (mCurrentState != State.EXPANDED) {
                onStateChanged(appBarLayout, State.EXPANDED)
            }
            State.EXPANDED
        } else if (Math.abs(i) >= appBarLayout.totalScrollRange) {
            if (mCurrentState != State.COLLAPSED) {
                onStateChanged(appBarLayout, State.COLLAPSED)
            }
            State.COLLAPSED
        } else {
            if (mCurrentState != State.IDLE) {
                onStateChanged(appBarLayout, State.IDLE)
            }
            State.IDLE
        }
    }

    abstract fun onStateChanged(
        appBarLayout: AppBarLayout?,
        state: State?
    )
}

Here is the listener:

  appbar.addOnOffsetChangedListener(object : AppBarStateChangeListener() {
        override fun onStateChanged(
            appBarLayout: AppBarLayout?,
            state: State?
        ) {
            if(state == State.COLLAPSED){
                LayoutBottom.visibility = View.GONE
            }else if(state == State.EXPANDED){
                LayoutBottom.visibility = View.VISIBLE
            }
        }
    })