How to find a spinner's displayed drop down views

My company's app supports changing the theme dynamically at runtime without having to restart the current Activity. It does this by walking the View tree and applying styles to each View that is configured to support it. The issue I'm running into, however, is that the drop down Views that are displayed for Spinners are never found when walking the View tree. This is the code for finding each View from the Activity:

void applyTheme(final int resourceId) {
	setTheme(resourceId);

	// Apply the theme to the activity's view.
	styleView(findViewById(android.R.id.content));

	// Apply the theme to any dialog fragments.
	final List<Fragment> fragments = getSupportFragmentManager().getFragments();
	for (final Fragment fragment : fragments) {
		if (fragment instanceof DialogFragment) {
			final Dialog dialog = ((DialogFragment)fragment).getDialog();
			if (dialog != null) {
				final Window window = dialog.getWindow();
				if (window != null) {
					styleView(window.getDecorView());
				}
			}
		}
	}
}

void styleView(final View view) {
	// Apply styling here.
	...

	// Recursively find all children and apply the theme to them.
	if (view instanceof ViewGroup) {
		final ViewGroup viewGroup = (ViewGroup)view;
		for (int i = 0; i < viewGroup.getChildCount(); i++) {
			styleView(viewGroup.getChildAt(i));
		}
	}
}

The drop down views are not found no matter if the parent Spinner is defined in the Activity, a Fragment, or a DialogFragment. If the drop down Views are visible to the user, is there any way to actually retrieve references to them?

This answer provided me a means to find all Views, including those of PopupWindows. Unfortunately, it makes use of reflection and is not guaranteed to work on all API versions, but it appears to work on the APIs that our app supports (I tested on APIs 19 and 28). This is the result of the changes to applyTheme():

private Object wmgInstance = null;
private Method getViewRootNames = null;
private Method getRootView = null;

private void applyTheme(final int resourceId)
{
	setTheme(resourceId);

	try
	{
		// Find all possible root views (the Activity, any PopupWindows, and Dialogs). This logic should work with APIs 17-28.
		if (wmgInstance == null)
		{
			final Class wmgClass = Class.forName("android.view.WindowManagerGlobal");
			wmgInstance = wmgClass.getMethod("getInstance").invoke(null, (Object[])null);

			getViewRootNames = wmgClass.getMethod("getViewRootNames");
			getRootView = wmgClass.getMethod("getRootView", String.class);
		}

		final String[] rootViewNames = (String[])getViewRootNames.invoke(wmgInstance, (Object[])null);

		for (final String viewName : rootViewNames)
		{
			final View rootView = (View)getRootView.invoke(wmgInstance, viewName);
			styleView(rootView);
		}
	}
	catch (Exception e)
	{
		// Log the exception.
	}
}

This logic successfully allowed me to update the Spinner's drop down Views when they were visible during a theme change. However, there still remained an issue that if the Spinner's drop down Views were created before the theme change occurred, but the drop down was closed at the time of the theme change, then re-opening the Spinner showed the Views using the old theme. The way I handled this was just to call styleView() on the View within my adapter's getDropDownView().