Java - PaintComponent 中的 MouseListener Action 事件

Question

这里我有一个代码，它使用paintComponent在mouseClicked位置绘制一个矩形。我可以获得输出消息，但任何与图形和.draw()相关的东西都不起作用。

代码:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

public final class testclass extends JFrame {

    static JPanel p;
    Timer t;
    int x = 1;
    int y = 1;
    int xspeed = 1;
    int yspeed = 1;

    public testclass() {
        initComponents();
        this.setBounds(100, 300, 500, 500);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        t.start();
        this.add(p);
    }

    public void initComponents() {
        final ActionListener action = new ActionListener() {

            public void actionPerformed(ActionEvent evt) {
                System.out.println("Hello!");
                p.repaint();
            }
        };

        t = new Timer(50, action);
        p = new JPanel() {

            public void paintComponent(Graphics g) {
                super.paintComponent(g);
                final Graphics2D gD = (Graphics2D) g;
                moveBALL();
                gD.drawOval(x, y, 25, 25);

                p.addMouseListener(new MouseListener() {

                    @Override
                    public void mouseReleased(MouseEvent e) {
                        System.out.println("a");
                    }

                    @Override
                    public void mousePressed(MouseEvent e) {
                        System.out.println("b");
                    }

                    @Override
                    public void mouseExited(MouseEvent e) {
                        System.out.println("c");
                    }

                    @Override
                    public void mouseEntered(MouseEvent e) {
                        System.out.println("d");
                    }

                    @Override
                    public void mouseClicked(MouseEvent e) {
                        gD.drawRect(e.getX(), e.getY(), 10, 60);
                        gD.setColor(Color.green);
                        System.out.println("clicked");
                    }
                });
            }

            void moveBALL() {
                x = x + xspeed;
                y = y + yspeed;
                if (x < 0) {
                    x = 0;
                    xspeed = -xspeed;
                } else if (x > p.getWidth() - 20) {
                    x = p.getWidth() - 20;
                    xspeed = -xspeed;
                }
                if (y < 0) {
                    y = 0;
                    yspeed = -yspeed;
                } else if (y > p.getHeight() - 20) {
                    y = p.getHeight() - 20;
                    yspeed = -yspeed;
                }
            }
        };
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            public void run() {
                new testclass().setVisible(true);
                p.setBackground(Color.WHITE);
            }
        });
    }
}

在这个程序中实现 mouseListener() 的正确方法是什么？
谢谢。

Answer 1

关于当前代码的一些建议:

观察类命名方案，即 testclass应该是 TestClass甚至更好Test (但那是挑剔)。所有类名都以大写字母开头，之后的每个新词都大写。

不要扩展JFrame不必要的。

不要调用setBounds在 JFrame而是使用适当的LayoutManager和/或覆盖 getPreferredSize()的 JPanel并返回适合其内容的尺寸。

随时调用pack()在 JFrame在将其设置为可见之前(考虑到上述情况)。

使用MouseAdapter对比 MouseListener

不要调用moveBall()在 paintComponent而是在您的 Timer 中调用它重新绘制屏幕，​​不仅设计稍微好一点，而且我们也不应该在绘制方法中执行可能长时间运行的任务。

至于你的问题，我认为你的逻辑有点歪曲。

一种方法是看到 Rectangle (或 Rectangle2D )被它自己的自定义类替换(这将允许我们存储颜色等属性)。你的球也会有自己的类，它有方法 moveBall()。及其属性如 x和 y位置等。在每个 repaint()您的 JPanel会调用方法来移动球， JPanel本身可以包装 moveBall()在它自己的公共(public)方法中，我们可以从重绘屏幕的计时器中调用它。

这是一个实现了上述修复的代码示例(请分析它，如果您有任何问题，请告诉我):

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Rectangle2D;
import java.util.ArrayList;
import javax.swing.*;

public class Test {

    private MyPanel p;
    private Timer t;

    public Test() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        initComponents();
        frame.add(p);

        frame.pack();
        frame.setVisible(true);

        t.start();
    }

    private void initComponents() {
        final ActionListener action = new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent evt) {
                p.moveEntities();//moves ball etc
                p.repaint();
            }
        };

        t = new Timer(50, action);
        p = new MyPanel();

        p.addMouseListener(new MouseAdapter() {
            @Override
            public void mouseClicked(MouseEvent e) {
                p.addEntity(e.getX(), e.getY(), 10, 50, Color.GREEN);
                System.out.println("clicked");
            }
        });

        p.setBackground(Color.WHITE);
    }

    public static void main(String args[]) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Test();
            }
        });
    }
}

class MyPanel extends JPanel {

    int width = 300, height = 300;
    ArrayList<MyRectangle> entities = new ArrayList<>();
    MyBall ball = new MyBall(10, 10, 25, 25, Color.RED, width, height);

    void addEntity(int x, int y, int w, int h, Color c) {
        entities.add(new MyRectangle(x, y, w, h, c));
    }

    void moveEntities() {
        ball.moveBALL();
    }

    @Override
    protected void paintComponent(Graphics grphcs) {
        super.paintComponent(grphcs);
        Graphics2D g2d = (Graphics2D) grphcs;

        g2d.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        g2d.setColor(ball.getColor());
        g2d.fillOval((int) ball.x, (int) ball.y, (int) ball.width, (int) ball.height);

        for (MyRectangle entity : entities) {
            g2d.setColor(entity.getColor());
            g2d.fillRect((int) entity.x, (int) entity.y, (int) entity.width, (int) entity.height);
        }
    }

    @Override
    public Dimension getPreferredSize() {
        return new Dimension(width, height);
    }
}

class MyRectangle extends Rectangle2D.Double {

    Color color;

    public MyRectangle(double x, double y, double w, double h, Color c) {
        super(x, y, w, h);
        color = c;
    }

    public void setColor(Color color) {
        this.color = color;
    }

    public Color getColor() {
        return color;
    }
}

class MyBall extends Ellipse2D.Double {

    int xspeed = 1;
    int yspeed = 1;
    Color color;
    private final int maxWidth;
    private final int maxHeight;

    public MyBall(double x, double y, double w, double h, Color c, int maxWidth, int maxHeight) {
        super(x, y, w, h);
        color = c;
        this.width = w;//set width and height of Rectangle2D
        this.height = h;
        //set max width and height ball can move
        this.maxWidth = maxWidth;
        this.maxHeight = maxHeight;
    }

    public void setColor(Color color) {
        this.color = color;
    }

    public Color getColor() {
        return color;
    }

    void moveBALL() {
        x = x + xspeed;
        y = y + yspeed;
        if (x < 0) {
            x = 0;
            xspeed = -xspeed;
        } else if (x > maxWidth - ((int) getWidth() / 2)) {// i dont like hard coding values its not good oractice and resuaibilty is diminshed
            x = maxWidth - ((int) getWidth() / 2);
            xspeed = -xspeed;
        }
        if (y < 0) {
            y = 0;
            yspeed = -yspeed;
        } else if (y > maxHeight - ((int) getHeight() / 2)) {
            y = maxHeight - ((int) getHeight() / 2);
            yspeed = -yspeed;
        }
    }
}