<com.google.android.exoplayer2.ui.PlayerView
    android:id="@+id/player_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    app:controller_layout_id="@layout/exo_controls" />

fun toggleController() {
    val playerView = findViewById<PlayerView>(R.id.player_view)
    val controlsVisible = // ???
    if (controlsVisible) {
        playerView.hideController()
    } else {
        playerView.showController()
    }
}