Can't make spinner's scrollbar always visible (Android)
Spinner does not have a scrollbar, Hence you are getting NullPointerException.
The popup shown by spinner has a scrollbar. So you need to change the properties of the ListView shown by spinner. But ListView itself is not exposed by Spinner by any public methods.
Even if you get the ListPopupWindow by reflection, a further problem arises, that ListPopupWindow's ListView is only created after you click the Spinner.
But OnClickListener of the Spinner cannot be registered , to set the ListView Properties after the show.
You could create a Custom Spinner with performClick overridden and then get mPopup by reflection. and use mPopup.getListView().setScrollbarFadingEnabled(false)
But If you are going to create a custom Spinner, i believe it is easier to implement the whole popup to suit your needs than using reflection.