scrollPane 不起作用，所以我想知道缺少什么

Question

我正在尝试制作滚动条。它已经显示在面板中，但它就像下面没有任何东西一样，所以它不会下降。这是我的代码（所有库都已添加）：

JPanel panel = new JPanel();

panel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));

panel.setBackground(Color.WHITE);

panel.setBounds(10, 66, 360, 705);

add(panel);

panel.setLayout(null);

JScrollPane scrollPane = new JScrollPane();

scrollPane.setBounds(345, 0, 20, 500);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

scrollPane.getVerticalScrollBar().setUnitIncrement(10);

scrollPane.setVisible(true);

panel.setPreferredSize(new Dimension(WIDTH,10));

scrollPane.setAutoscrolls(true);

panel.add(scrollPane);

Answer 1

试试

JPanel panel = new JPanel();

panel.setBorder(new BevelBorder(BevelBorder.LOWERED, null, null, null, null));

panel.setBackground(Color.WHITE);

panel.setBounds(10, 66, 360, 705);

panel.setLayout(null);

JScrollPane scrollPane = new JScrollPane(panel);

scrollPane.setBounds(345, 0, 20, 500);
scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

scrollPane.setHorizontalScrollBarPolicy(JScrollPane.HORIZONTAL_SCROLLBAR_ALWAYS);

scrollPane.getVerticalScrollBar().setUnitIncrement(10);

scrollPane.setVisible(true);

panel.setPreferredSize(new Dimension(WIDTH,10));

scrollPane.setAutoscrolls(true);

add(scrollPane);

注意从 add(panel) 到 add(scrollPane) 的变化以及新的 JScrollPane(panel);线