Avoid taking window focus by Android Spinner's Dropdown to keep setSystemUiVisibility flags (such as Immersive Mode).

AvoidSpinnerDropdownFocus.java

import android.widget.ListPopupWindow;
import android.widget.PopupWindow;
import android.widget.Spinner;

public static void avoidSpinnerDropdownFocus(Spinner spinner) {
    try {
        Field listPopupField = Spinner.class.getDeclaredField("mPopup");
        listPopupField.setAccessible(true);
        Object listPopup = listPopupField.get(spinner);
        if (listPopup instanceof ListPopupWindow) {
            Field popupField = ListPopupWindow.class.getDeclaredField("mPopup");
            popupField.setAccessible(true);
            Object popup = popupField.get((ListPopupWindow) listPopup);
            if (popup instanceof PopupWindow) {
                ((PopupWindow) popup).setFocusable(false);
            }
        }
    } catch (NoSuchFieldException e) {
        e.printStackTrace();
    } catch (IllegalAccessException e) {
        e.printStackTrace();
    }
}

AvoidSpinnerDropdownFocus.kt

import android.widget.ListPopupWindow
import android.widget.PopupWindow
import android.widget.Spinner

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()
    }
}

When you call this method to prevent exit immersive mode?

@CheckHelzio It should be called before showing dropdown.

Thank you for the very useful code snippet, but I noticed it does not work with AppCompatSpinner (appcompat v1.1.0-alpha04).

Here is a bit modified version which compatible with AppCompatSpinner 👏

import android.widget.PopupWindow
import android.widget.Spinner

fun Spinner.avoidDropdownFocus() {
    try {
        val isAppCompat = this is androidx.appcompat.widget.AppCompatSpinner
        val spinnerClass = if (isAppCompat) androidx.appcompat.widget.AppCompatSpinner::class.java else Spinner::class.java
        val popupWindowClass = if (isAppCompat) androidx.appcompat.widget.ListPopupWindow::class.java else android.widget.ListPopupWindow::class.java

        val listPopup = spinnerClass
                .getDeclaredField("mPopup")
                .apply { isAccessible = true }
                .get(this)
        if (popupWindowClass.isInstance(listPopup)) {
            val popup = popupWindowClass
                    .getDeclaredField("mPopup")
                    .apply { isAccessible = true }
                    .get(listPopup)
            if (popup is PopupWindow) {
                popup.isFocusable = false
            }
        }
    } catch (e: Exception) {
        e.printStackTrace()
    }
}

shame on Android team!

apparently this breaks my espresso test, not sure why. It still works with manual pressing the item though.

Thanks for nice solution!

It's working nice, but with setting it to non focusable, it loses the click outside to close functionality. Unfortunately I can't find any workaround, and I tried many.

isOutsideTouchable = true works for me fwiw