如何设置JFrame大小以适合CardLayout显示的JPanel？

如何设置JFrame大小以适合CardLayout显示的JPanel？

通常是：如果您遇到布局问题，请 始终 使用适当的LayoutManager解决它。 切勿 调整组件的大小提示以达到您的目标。

在这种情况下，调整CardLayout特别容易。默认情况下，它将其prefSize计算为所有卡的prefSizes的最大值。只需子类化并实现以返回当前可见卡的prefSize（加上插图）即可：

public static class MyCardLayout extends CardLayout {    @Override    public Dimension preferredLayoutSize(Container parent) {        Component current = findCurrentComponent(parent);        if (current != null) { Insets insets = parent.getInsets(); Dimension pref = current.getPreferredSize(); pref.width += insets.left + insets.right; pref.height += insets.top + insets.bottom; return pref;        }        return super.preferredLayoutSize(parent);    }    public Component findCurrentComponent(Container parent) {        for (Component comp : parent.getComponents()) { if (comp.isVisible()) {     return comp; }        }        return null;    }}

使用该方法（借用@mKorbel的示例），主要方法完全缩小了：

private static void createAndShowUI() {    final CardLayout cardLayout = new MyCardLayout();    final JPanel cardHolder = new JPanel(cardLayout);    final Jframe frame = new Jframe("MultiSizedPanels");    JLabel[] labels = {        new JLabel("Small Label", SwingConstants.CENTER),        new JLabel("Medium Label", SwingConstants.CENTER),        new JLabel("Large Label", SwingConstants.CENTER)};    for (int i = 0; i < labels.length; i++) {        int padding = 50 * (i + 1);        Border lineBorder = BorderFactory.createCompoundBorder( BorderFactory.createLineBorder(Color.blue), BorderFactory.createEmptyBorder(padding, padding, padding, padding));        labels[i].setBorder(lineBorder);        JPanel containerPanel = new JPanel();        containerPanel.add(labels[i]);        cardHolder.add(containerPanel, String.valueOf(i));    }    JButton nextButton = new JButton("Next");    nextButton.addActionListener(new ActionListener() {        @Override        public void actionPerformed(ActionEvent e) { cardLayout.next(cardHolder); frame.pack();        }    });    JPanel btnHolder = new JPanel();    btnHolder.add(nextButton);    frame.add(cardHolder, BorderLayout.CENTER);    frame.add(btnHolder, BorderLayout.SOUTH);    frame.setDefaultCloseOperation(Jframe.EXIT_ON_CLOSE);    frame.pack();    frame.setLocation(150, 150);    frame.setVisible(true);}