Java Swing 上的事件链

Question

我基本上想制作一个用户可以在其中绘制分段线的单一窗口应用程序。申请流程应该是：

1. 用户单击应用程序的唯一按钮以启动进程
2. 用户通过单击段的第一个点进行选择
3. 用户通过单击段的第二个点进行选择

我已经有了以下代码：

public class LineEditor extends JComponent{

        private class Point{
            int x, y;

            public Point(int x, int y){
                this.x = x;
                this.y = y;
            }
        }
        private class Line{
            Point a, b;

            public Line(Point a, Point b){
                this.a = a;
                this.b = b;
            }
        }

        private ArrayList<Line> lines = new ArrayList<Line>();

        public void setLine(Point a, Point b){
            lines.add(new Line(a, b));
            repaint();
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            for (Line line : lines) {
                g.setColor(line.color);
                g.drawLine(line.a.x, line.a.y, line.b.x, line.b.y);
            }
        }

        public static void main(String[] args){
            int height = 500, width = 500;

            JFrame frame = new JFrame();
            frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

            // Properties of the main window
            frame.setAlwaysOnTop(true);
            final LineEditor lineEditor = new LineEditor();
            lineEditor.setPreferredSize(new Dimension(width, height));

            JPanel panelCanvas = new JPanel(); 
            panelCanvas.setPreferredSize(new Dimension(width, height));


            JPanel secondaryPanel = new JPanel();
            JButton addLineButton = new JButton("Add new line");
            secondaryPanel.add(addLineButton);


            frame.getContentPane().add(lineEditor, BorderLayout.CENTER);
            frame.getContentPane().add(panelCanvas, BorderLayout.CENTER);
            frame.getContentPane().add(secondaryPanel, BorderLayout.NORTH);

            panelCanvas.addMouseListener(new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    int x = e.getX();
                    int y = e.getY();
                }
            });

            addLineButton.addActionListener(new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    // x
                }
            });

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

        }
    }

我不知道怎么做：

1. 仅在用户按下按钮后激活 panelCanvas.addMouseListener。
2. 从 addLineButton.addActionListener 获取鼠标坐标（点击后），这样我就可以创建两个 Point 对象，然后调用 lineEditor.setLine(pointA, pointB)

我想实现以下目标：

addLineButton.addActionListener(new ActionListener() {
    @Override
    public void actionPerformed(ActionEvent e) {

        // Wait for the first user click
        int x1 = mouseListener.getX();
        int y1 = mouseListener.getY();
        Point a = new Point(x1, y1);

        // Wait for the second user click
        int x2 = mouseListener.getX();
        int y2 = mouseListener.getY();
        Point b = new Point(x2, y2);

        lineEditor.setLine(a, b);
    }
});

Answer 1

我终于通过在绘制新线时强制用户遵循下一个流程来解决问题：

1. 当用户第一次尝试单击线条的第一个点时，会打开一个 JColor 框，以便轻松选择线条颜色。
2. 然后，用户必须单击要设置线的第一个点的第一个点。
3. 线的第二个点将位于用户释放点击按钮的坐标中。

请注意，这只是我正在寻找的一种方法（第一次点击&释放=第一个点，第二次点击&释放=第二个点），但我仍然认为它对于挥杆初学者来说可能是一个不错的示例。

public class LineEditor extends JComponent{

    private static class Point{
        final int x, y;

        public Point(int x, int y){
            this.x = x;
            this.y = y;
        }
    }
    private static class Line{
        final Point a, b;  
        final Color color;

        public Line(Point a, Point b, Color color) {
            this.a = a;
            this.b = b;
            this.color = color;
        }               
    }

    private final LinkedList<Line> lines = new LinkedList<Line>();

    public void addLine(int xa, int ya, int xb, int yb, Color color) {
        lines.add(new Line(new Point(xa, ya), new Point(xb, yb), color));        
        repaint();
    }

    public void clearScreen() {
        if(lines.size() > 0){
            lines.remove(lines.getLast());
            repaint();
        }   
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        for (Line line : lines) {
            g.setColor(line.color);
            g.drawLine(line.a.x, line.a.y, line.b.x, line.b.y);
        }
    }

    public static void main(String[] args) {
        int width, height;
        width = 500;
        height = 500;

        JFrame backgroundFrame = new JFrame();
        backgroundFrame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);

        final LineEditor lineEditor = new LineEditor();
        lineEditor.setPreferredSize(new Dimension(width, height));
        backgroundFrame.getContentPane().add(lineEditor, BorderLayout.CENTER);

        JPanel buttonsPanel = new JPanel();
            JButton clearScreen = new JButton("Remove last line");
            buttonsPanel.add(clearScreen);
            backgroundFrame.getContentPane().add(buttonsPanel, BorderLayout.SOUTH);

        backgroundFrame.addMouseListener(new MouseAdapter() {
            int ax, ay, bx, by;
            Color color;
            Boolean colorSetted = false;
            @Override
            public void mouseEntered(MouseEvent e) {
                if(!colorSetted){
                    JColorChooser colorChooser =new JColorChooser();
                    this.color = colorChooser.showDialog(null, "Select a color", Color.BLACK);
                    colorSetted = true;
                }
            }
            @Override
            public void mousePressed(MouseEvent e) {
                ax = e.getX();
                ay = e.getY();
                System.out.println("Mouse pressed: " + ax + ", " + ay);


            }

            @Override
            public void mouseReleased(MouseEvent e) {
                bx = e.getX();
                by = e.getY();
                System.out.println("Mouse released: " + bx + ", " + by);
                lineEditor.addLine(ax, ay, bx, by, color);
                colorSetted = false;
            }
        });

        clearScreen.addActionListener(new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                lineEditor.clearScreen();
            }
        });

        backgroundFrame.pack();
        backgroundFrame.setVisible(true);
    }
}