State Machine in View with a Sealed Class from Kotlin

TabbedListActivity.kt

    override fun onStart() {
        viewModel.tabbedListLiveData.observe(this, Observer {
            when (it) {
                is ErrorState -> {
                    showProgress(false)
                    showErrorView(it.errorMessage, it.errorColor)
                }
                is InProgressState -> showProgress(true)
                is OfflineState -> {
                    showProgress(false)
                    displayList(it.listElements)
                    hideTabs()
                }
                is ListState -> {
                    showProgress(false)
                    displayList(it.listElements, it.totalItems)
                    displayTabs(it.currentTabId, it.tabs)
                }
            }
        })
    }