Java Swing Repaint 速度慢或不工作

Question

我正在尝试使用布尔标志根据按钮单击绘制图形。之前，我在 ShapeGUI 类中将布尔值设置为公共静态布尔类型，并使用 Shape.draw 在 ShapeListener 中调用它并且有效，尽管变出绘图大约需要 10 秒。

现在我在 ShapeListener 类本身中设置布尔标志。现在它要么不重新粉刷，要么非常慢。如何使绘图在单击按钮时立即显示？

public class ShapeGUI extends JFrame
{
    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;
    public ShapeGUI()
    {
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        //setLayout(new FlowLayout());
        setLocationRelativeTo(null);
        JMenuBar menu = new JMenuBar();
        JMenu file = new JMenu("File");
        menu.add(file);
        JMenuItem save = new JMenuItem("Save Information");
        JMenuItem exit = new JMenuItem("Exit");
        file.add(save);
        file.add(exit);               
        setJMenuBar(menu);
        ShapeListener test = new ShapeListener();        
        JButton button = new JButton("Hello"); 
        test.setBackground(Color.CYAN);
        button.addActionListener(new ShapeListener());
        test.add(button); 
        add(test);
//followed this person's advice        
//First off, your drawing should be done in a paintComponent method override that is held in a class that extends JPanel. Next, this class could have a boolean variable that the paintComponent uses to decide if it will draw a rectangle or not. The button press simply sets the boolean variable and calls repaint on the drawing JPanel.
    }
}
    public class ShapeListener extends JPanel implements ActionListener
    {
    boolean draw = false;
    Shape s = new Circle();
    Shape a = new Rectangle();
    @Override
    public void actionPerformed(ActionEvent e) 
    {
        draw = true;
        repaint();
    }
    @Override
    public void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        if(draw)
        {
        s.draw(g);
        }
        else
        {
            a.draw(g);
        }
    }
}

Answer 1

你的逻辑有点不对劲...

ShapeListener test = new ShapeListener(); // First instance
JButton button = new JButton("Hello");
test.setBackground(Color.CYAN);
button.addActionListener(new ShapeListener()); // Second instance...
test.add(button);
add(test);

创建 ShapeListener 类的两个实例，将一个添加到容器，并将另一个用作操作侦听器。 双方都不会知道对方，这意味着你可以点击到奶牛回家，第一次ShapeListener永远不会改变。

此外，除非您打算覆盖ShapeListener窗格的preferredSize方法，否则我会在框架上使用类似BorderLayout的东西，以确保面板布局正确，否则看起来面板没有被绘制......

尝试类似...

public class ShapeGUI extends JFrame {
    public static final int WIDTH = 500;
    public static final int HEIGHT = 500;
    public ShapeGUI() {
        setSize(WIDTH, HEIGHT);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
        JMenuBar menu = new JMenuBar();
        JMenu file = new JMenu("File");
        menu.add(file);
        JMenuItem save = new JMenuItem("Save Information");
        JMenuItem exit = new JMenuItem("Exit");
        file.add(save);
        file.add(exit);
        setJMenuBar(menu);
        setLayout(new BorderLayout());
        ShapeListener test = new ShapeListener();
        JButton button = new JButton("Hello");
        test.setBackground(Color.CYAN);
        button.addActionListener(test);
        test.add(button);
        add(test);
        setVisible(true);
    }
    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }
                new ShapeGUI();
            }
        });
    }
    public class ShapeListener extends JPanel implements ActionListener {
        Shape s = new Ellipse2D.Float(0, 0, 20, 20);
        Shape a = new Rectangle2D.Float(0, 0, 20, 20);
        private Shape paintMe = a;
        @Override
        public void actionPerformed(ActionEvent e) {
            paintMe = s;
            repaint();
        }
        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            int x = (getWidth() - paintMe.getBounds().width) / 2;
            int y = (getHeight() - paintMe.getBounds().height) / 2;
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.translate(x, y);
            g2d.draw(paintMe);
            g2d.dispose();
        }
    }
}

相反。。。