I'm trying to achieve a full-screen application, where the user doesn't have any access to the status- & navigation-bar.

Preferably I would want them to be removed completely, but from what I've read this is not possible unless you root the device

So my question basically is: How do I hide the navigation-bar icons, when I show the pop-up menu?

BEFORE

AFTER

So far, I have tried:

• Calling hideNavigation() before & after the pop-up menu is shown
• Calling hideNavigation() in onCreate(), onResume() & onWindowFocusChanged()
• Requesting focus to another view
• Trying to clear the focus from the drop-down (Failed attempt, didn't really find a way to do this)
• Changing the icon colors, "faking" it would be hidden (Failed attempt, didn't really find a way to do this)
• Using hideNavigation() in combination with Handler (Failed attempt, maybe I didn't do it correctly)
• Trying to configure some COSU/KIOSK-mode options (Perhaps there is some way to complete disable the whole navigation-bar? I haven't found a way to hide the back-button yet)

ACTIVITY

    class PinCodeActivity, HasTitleBar {
        override fun onCreate(savedInstanceState: Bundle?) {
            super.onCreate(savedInstanceState)
            setContentView(R.layout.activity_pin_code)
            initTitleBarWith(this)
            hideNavigation()
        }

        override fun onResume() {
            super.onResume()
            hideNavigation()
        }

        fun hideNavigation() {
            window.decorView.apply {
                systemUiVisibility = FLAGS
            }
        }

        override fun onWindowFocusChanged(hasFocus: Boolean) {
            super.onWindowFocusChanged(hasFocus)
            hideNavigation()
        }
    }

const val FLAGS = (View.SYSTEM_UI_FLAG_LOW_PROFILE or View.SYSTEM_UI_FLAG_LAYOUT_HIDE_NAVIGATION or View.SYSTEM_UI_FLAG_LAYOUT_FULLSCREEN or View.SYSTEM_UI_FLAG_HIDE_NAVIGATION or View.SYSTEM_UI_FLAG_FULLSCREEN or View.SYSTEM_UI_FLAG_IMMERSIVE_STICKY)

TITLE-BAR

    fun HasTitleBar.initTitleBarWith(activity: Activity, resId: Int = R.id.titleBar) {
        val langButton = activity.findViewById<View>(resId).findViewById<Button>(R.id.tbLanguageChoiceBtn)
        val wrapper = ContextThemeWrapper(activity, R.style.MyPopupMenu)
        val popupMenu = PopUpLanguageMenu(wrapper, langButton)
        langButton.setOnClickListener {
            activity.hideNavigation()
            popupMenu.showMenu()
            activity.hideNavigation()
        }
    }

POP-UP MENU

    class PopUpLanguageMenu constructor(context: Context, view: View) : PopupMenu(context, view) {

        private var popupHelper: MenuPopupHelper

        init {
            val popUpMenu = PopupMenu(context, view).apply {
                inflate(R.menu.menu_language_dropdown)
            }

            popupHelper = MenuPopupHelper(context, popUpMenu.menu as MenuBuilder, view)
            popupHelper.run {
                gravity = Gravity.END
                setForceShowIcon(true)
            }
        }

        fun showMenu() {
            popupHelper.show()
        }
    }

EXPECTED RESULT: Navigation-bar & it's icons are hidden, after the pop-up menu is shown, the icons are still HIDDEN

ACTUAL RESULT: Navigation-bar & it's icons are hidden, after the pop-up menu is shown, the icons are SHOWN

The nav bar re-appears because there is a new DecorView (PopupDecorView) is newly drawn on the top of the Views stack, which isn't affected by your FLAGs set before.

There is no silver bullet here, my approach is to dig into the WindowManagerGlobal by reflection and catch out the peek View, apply the system FLAGs on it again, so after the PopupMenu shows up, it manages to hide the Navigation bar right after that (there is still, a show up from the Navigation Bar once).

Here is the code:

override fun onWindowFocusChanged(hasFocus: Boolean) {
    super.onWindowFocusChanged(hasFocus)
    if (hasFocus) {
        hideNavigation()
    } else {
        // When PopupMenu appears, the current Activity looses the focus
        setFlagsOnThePeekView() // Hijack to the current peek view, apply the Flags on it
    }
}

@SuppressLint("PrivateApi")
fun setFlagsOnThePeekView() {
    try {
        val wmgClass = Class.forName("android.view.WindowManagerGlobal")
        val wmgInstance = wmgClass.getMethod("getInstance").invoke(null)
        val viewsField = wmgClass.getDeclaredField("mViews")
        viewsField.isAccessible = true

        val views = viewsField.get(wmgInstance) as ArrayList<View>
        // When the popup appears, its decorView is the peek of the stack aka last item
        views.last().apply { 
            systemUiVisibility = FLAGS
            setOnSystemUiVisibilityChangeListener {
                systemUiVisibility = FLAGS
            }
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }
}