AppBarLayoutViewHolder

AppBarLayoutViewHolder.kt

import androidx.coordinatorlayout.widget.CoordinatorLayout
import com.google.android.material.appbar.AppBarLayout
import java.io.Closeable

class AppBarLayoutViewHolder(appBarLayout: AppBarLayout) : Closeable {

    var expandable: Boolean = true
        set(value) {
            field = value
            layout?.setExpanded(value)
            layout?.setLiftable(value)

            // https://stackoverflow.com/a/46973974/1006741
            val params = layout?.layoutParams as CoordinatorLayout.LayoutParams
            if (params.behavior == null)
                params.behavior = DisableableAppBarLayoutBehavior(layout?.context)
            val behaviour = params.behavior as DisableableAppBarLayoutBehavior

            behaviour.isEnabled = value
        }

    var layout by weak<AppBarLayout?>()

    init {
        layout = appBarLayout
    }

    override fun close() {
        layout = null
    }
}