Spinner in Full Screen android app is showing status bar

I have an android app. I have a spinner called dd1 defined in my mainactivity.xml.

I have the onItemSelected method defined in a fragment.

The app runs full screen, i.e. hides the navigation and status bar. Everything is fine. But the moment I touch the spinner, the status bar pops up, and never goes back.

I need to ensure that the status bar remains hidden.

Attempt to solve

I read this SO Question. It already refers to this GIT gist.

In my Fragment, just before the override fun onCreateView I define:

fun Spinner.avoidDropdownFocus() {
        try {
            val listPopup = Spinner::class.java
                .getDeclaredField("mPopup")
                .apply { isAccessible = true }
                .get(this)
            if (listPopup is ListPopupWindow) {
                val popup = ListPopupWindow::class.java
                    .getDeclaredField("mPopup")
                    .apply { isAccessible = true }
                    .get(listPopup)
                if (popup is PopupWindow) {
                    popup.isFocusable = false
                }
            }
        } catch (e: Exception) {
            e.printStackTrace()
        }
    }

Then, in the onItemSelected, I have:

 dd1.onItemSelectedListener =  object : AdapterView.OnItemSelectedListener {
            override fun onItemSelected(parent: AdapterView<*>?, view: View?, position: Int, id: Long) {

                // getWindow().addFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN);
                

                dd1.avoidDropdownFocus()
    ... // do my thing
 }
} 

This does not work. I am using Android 10, but on a DJI Remote Control.

Question

How do I force the status bar to remain hidden during the runtime of the app, despite activating the spinner(s)?

Thank you

Please avoid this reflection way.
May be it's an issue before Android 11 that status bar pops up when spinner opens, 'cause I can reproduce it on Android 9, but can't on Android 11.

So, I think you can ignore the pop-up issue.

And to avoid status bar remaining visible when spinner closed, hide status bar manually in your activity:

    override fun onWindowFocusChanged(hasFocus: Boolean) {
        super.onWindowFocusChanged(hasFocus)
        if (hasFocus) {
            WindowCompat.getInsetsController(window, window.decorView).apply {
                hide(WindowInsetsCompat.Type.statusBars())
                // Or instead hide statusBar and navigationBar together if required.
                //hide(WindowInsetsCompat.Type.systemBars())
            }
        }
    }

Updated 1: ---------

I found the statusbar pop-up issue is because of "Temporary full screen".
To implement full screen, we usually do these ways:

1. Stable full screen

Use Theme or window flag:

// Set theme to full screen or use a full screen theme from SDK.
<item name="android:windowFullscreen">true</item>

// Or set window flag in activity:
window.setFlags(
    WindowManager.LayoutParams.FLAG_FULLSCREEN,
    WindowManager.LayoutParams.FLAG_FULLSCREEN
)

In that way statusbar will not pop up when Spinner/PopupWindow shows.

2. "Temporary full screen"

Hide status bar via code:

// By insets controller 
WindowCompat.getInsetsController(window, window.decorView).apply {
    hide(WindowInsetsCompat.Type.statusBars())
}
// Or
window.decorView.systemUiVisibility =
    window.decorView.systemUiVisibility or View.SYSTEM_UI_FLAG_FULLSCREEN

// Usually, we will also set systembar's behavior so the hidden 
// statusbar will hide after a while when user swipe to show it.
WindowCompat.getInsetsController(window, window.decorView).apply {
            systemBarsBehavior = WindowInsetsControllerCompat.BEHAVIOR_SHOW_TRANSIENT_BARS_BY_SWIPE
        }

This way, status bar will pop up when Spinner/PopupWindow shows bellow Android 11 version.
To avoid it, use this code:

import androidx.appcompat.widget.AppCompatSpinner
import androidx.appcompat.widget.ListPopupWindow

// Note we should import androidx.appcompat.widget.ListPopupWindow
fun AppCompatSpinner.avoidDropdownFocus() {
    try {
        val popupDelegate =
            AppCompatSpinner::class.java
                .getDeclaredField("mPopup")
                .apply { isAccessible = true }
                .get(this)
        if (popupDelegate is ListPopupWindow) {
            val popup = ListPopupWindow::class.java
                .getDeclaredField("mPopup")
                .apply { isAccessible = true }
                .get(popupDelegate)
            (popup as? PopupWindow)?.apply {
                isFocusable = false
                // We need to call "update" to let 'focusable' to take effect.
                update()
            }
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }
}

Note this is only working for spinner dropdown mode, not for dialog mode.