JScrollPane没有显示任何内容

Question

我不熟悉渲染GUI并使用JScrollPane不会显示任何内容：

private JFormattedTextField IDEnterer;

private Cart cart;

private JFrame frame;

private JScrollPane jScrollPane;

public MainUserGUI(UUID uuid){
    frame = new JFrame("Current user: " + uuid.toString());
    cart = new Cart();

    jScrollPane = new JScrollPane(/*ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS, ScrollPaneConstants.HORIZONTAL_SCROLLBAR_AS_NEEDED*/);
    jScrollPane.setLayout(new ScrollPaneLayout());

    openUserGUI();
}

public void openUserGUI(){      
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setLocationRelativeTo(null);
    frame.setLayout(new BorderLayout());
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);

    JPanel iDPanel = new JPanel();
    iDPanel.add(Box.createHorizontalStrut(10));
    iDPanel.add(Box.createVerticalStrut(50));
    iDPanel.add(new JLabel("Enter an ID:"));
    iDPanel.add(getIntegerField(200, 20));
    iDPanel.add(getIntegerSubmitButton("Submit ID"));

    jScrollPane.add(new JLabel("Shopping cart:"));

    frame.add(iDPanel, BorderLayout.WEST);
    frame.add(jScrollPane, BorderLayout.EAST);
    frame.pack();
    frame.setVisible(true);
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
}

private void renderList(){
    JPanel p = new JPanel();
    jScrollPane.removeAll();
    jScrollPane.add(new JLabel("Shopping cart:"));
    int i = 0;
    for(Item item : getCartItems()){
        int j = i;
        JPanel panel = new JPanel();
        JButton removeOne = new JButton("Remove one");
        Action removeOneAction = new AbstractAction() {

            private static final long serialVersionUID = 1L;
            @Override
            public void actionPerformed(ActionEvent e) {
                new InformationEnterer().removeOne(cart, getCartItems()[j].getID());
                renderList();
            }
        };
        removeOne.addActionListener(removeOneAction);

        JButton remove = new JButton("Remove all");
        Action removeAllAction = new AbstractAction() {

            private static final long serialVersionUID = 1L;
            @Override
            public void actionPerformed(ActionEvent e) {
                new InformationEnterer().removeAll(cart, getCartItems()[j].getID());
                renderList();
            }
        };
        remove.addActionListener(removeAllAction);

        JLabel label = new JLabel(i + ": " + item.getName() + "(" + item.getID() + "), "
                + "Amount: " + cart.getCart().get(item.getID()) + ", "
                        + "Price: " + item.getPrice() * cart.getCart().get(item.getID()));

        panel.add(label);
        panel.add(removeOne);
        panel.add(remove);
        p.add(panel);
        i++;
    }
    jScrollPane.setViewportView(p);
    frame.pack();
    frame.setExtendedState(JFrame.MAXIMIZED_BOTH);
}

private Item[] getCartItems(){
    Item[] r = new Item[cart.getCart().size()];
    int i = 0;
    for(Integer integ : cart.getCart().keySet()){
        Item item = new Item(integ);
        r[i] = item;
        i++;
    }
    return r;
}
private JFormattedTextField getIntegerField(int width, int height){
    NumberFormat format = NumberFormat.getInstance();
    NumberFormatter formatter = new NumberFormatter(format);
    formatter.setValueClass(Integer.class);
    formatter.setMinimum(-1);
    formatter.setMaximum(Integer.MAX_VALUE);
    formatter.setCommitsOnValidEdit(true);
    formatter.setAllowsInvalid(false);
    IDEnterer = new JFormattedTextField(formatter);
    Dimension dimension = new Dimension(width, height);
    IDEnterer.setPreferredSize(dimension);
    return IDEnterer;
}

private JButton getIntegerSubmitButton(String text){
    JButton button = new JButton(text);
    Action action = new AbstractAction() {

        private static final long serialVersionUID = 1L;
        @Override
        public void actionPerformed(ActionEvent e) {
            if(IDEnterer != null){
                if(IDEnterer.getText().length() <= 0){
                    JOptionPane.showMessageDialog(null, "The ID can't be null", "Warning", JOptionPane.ERROR_MESSAGE);
                }else{
                    new InformationEnterer().addItem(cart, Integer.parseInt(IDEnterer.getText().replaceAll(",", "")));
                    renderList();
                    IDEnterer.setValue(null);
                }
            }
        }
    };
    button.addActionListener(action);
    return button;
}

我不知道为什么它没有显示任何东西，屏幕更新肯定是。提前谢谢你，

Whereisthemonkey

@VGR这是我的更新代码，它仍然无法正常工作