Java Swing 上的事件链

Question

我基本上想制作一个 window 应用程序，用户可以在其中绘制分段线。申请流程应该是：

用户单击应用程序的唯一按钮以启动进程
用户通过点击线段的第一个点进行选择
用户通过点击线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);

        }
    }

我不知道如何：

仅在用户按下按钮后激活 panelCanvas.addMouseListener。
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)

我想实现这样的目标：

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

我终于解决了这个问题，方法是在绘制新线时强制用户遵循下一个流程：

当用户第一次尝试点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。
然后，用户必须单击要设置线的第一个点的第一个点。
线的第二个点将位于用户释放点击按钮的坐标。

请注意，这只是我正在寻找的一种方法（第一次点击&释放=第一点，第二次点击&释放=第二点），但我仍然认为这对于挥杆初学者来说可能是一个很好的示例。

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);
    }
}

Java Swing 上的事件链

Events chain on Java Swing

java

swing

lines

draw