let popoverView = FSPopoverView()
popoverView.dataSource = self
popoverView.present(fromBarItem: barItem)

// data source
extension viewController: FSPopoverViewDataSource {
    
    func backgroundView(for popoverView: FSPopoverView) -> UIView? {
        let view = UIView()
        view.backgroundColor = .yellow
        return view
    }
    
    func contentView(for popoverView: FSPopoverView) -> UIView? {
        return contentView
    }
    
    func contentSize(for popoverView: FSPopoverView) -> CGSize {
        return .init(width: 100.0, height: 100.0)
    }
    
    func containerSafeAreaInsets(for popoverView: FSPopoverView) -> UIEdgeInsets {
        return view.safeAreaInsets
    }
    
    func popoverViewShouldDismissOnTapOutside(_ popoverView: FSPopoverView) -> Bool {
        return true
    }
}

let features: [Feature] = [.copy, .message, .db, .qr, .settings]
let items: [FSPopoverListItem] = features.map { feature in
    let item = FSPopoverListTextItem()
    item.image = feature.image
    item.title = feature.title
    item.isSeparatorHidden = false
    item.selectedHandler = { item in
        guard let item = item as? FSPopoverListTextItem else {
            return
        }
        print(item.title ?? "")
    }
    item.updateLayout()
    return item
}
items.last?.isSeparatorHidden = true
let listView = FSPopoverListView()
listView.items = items
listView.present(fromRect: sender.frame.insetBy(dx: 0.0, dy: -6.0), in: view)

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -> Bool {
    do {
        let appearance = FSPopoverView.fs_appearance()
        appearance.showsArrow = false
        appearance.showsDimBackground = true
        ...
    }
    return true
}