java - Repaint() 方法不会重新绘制需要的内容

Question

这就是我的任务。

我必须生成 4 张随机卡。之后，当按下“刷新”按钮时，卡片应再次随机化。我已经像这样实现了 repaint() 方法，但它不会改变卡片的显示方式。

public class FourCards extends JFrame {

        JLabel slot1 = new JLabel(getImage());
        JLabel slot2 = new JLabel(getImage());
        JLabel slot3 = new JLabel(getImage());
        JLabel slot4 = new JLabel(getImage());

    public FourCards() {

        JPanel CardsPanel = new JPanel(new GridLayout(1,4,5,5));
        add(CardsPanel);

        CardsPanel.add(slot1);
        CardsPanel.add(slot2);
        CardsPanel.add(slot3);
        CardsPanel.add(slot4);

        JButton jbtRefresh = new JButton("Refresh");

        JPanel ButtonPanel = new JPanel();
        this.add(ButtonPanel, BorderLayout.SOUTH);
        ButtonPanel.add(jbtRefresh);

        jbtRefresh.addActionListener(new ButtonListener());

        }

    public ImageIcon getImage() {

        ImageIcon temp = new ImageIcon("C:/resized/" + (int)(Math.random() * 52) + ".png");
        return temp;

    }

    public void update() {

        slot1 = new JLabel(getImage());
        slot2 = new JLabel(getImage());
        slot3 = new JLabel(getImage());
        slot4 = new JLabel(getImage());

    }

    public static void main(String[] args) {

        FourCards frame = new FourCards();
            frame.setTitle("Random 4 cards");
            frame.setSize(600,280);
            frame.setLocationRelativeTo(null);
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
            frame.setVisible(true);

    }

    class ButtonListener implements ActionListener {

        @Override
        public void actionPerformed(ActionEvent e) {

            update(); // get new images
            repaint();

        }

    }

}

Answer 1

当你这样做时

slot1 = new JLabel(getImage());
slot2 = new JLabel(getImage());
slot3 = new JLabel(getImage());
slot4 = new JLabel(getImage());

您没有更改 GUI。您正在更新 slotX 变量的值。您还应该替换 GUI 树中的实际组件。

尝试将 CardsPanel 设为成员变量，然后执行

CardsPanel.removeAll();
CardsPanel.add(new JLabel(getImage()));
CardsPanel.add(new JLabel(getImage()));
CardsPanel.add(new JLabel(getImage()));
CardsPanel.add(new JLabel(getImage()));