Java只addMouseListener一次

Question

我的程序中有一个组合框，其中包含三个选项“圆形”、“矩形”、“徒手画”。每个选项都连接到一个鼠标监听器。如果我在三个选项之间切换，鼠标监听器会给我带来一些问题。因此，我只想添加一次鼠标监听器(例如在构造函数中或在方法的开头或其他地方)。这是否可能，代码会是什么样子？如果不行的话还有其他办法可以解决吗？

public void actionPerformed(ActionEvent e) {      

         if (e.getSource().equals(comboBox)) {            

            JComboBox cb = (JComboBox)e.getSource();

                if (cb.getSelectedItem().equals("Rectangle")) {                
                contentPane.addMouseListener(new MouseAdapter() {       //First mouseListener     
                    @Override
                    public void mousePressed(MouseEvent e) {  
                        startX = e.getX();     
                        startY = e.getY(); 
                    }
                    @Override
                    public void mouseReleased(MouseEvent e) {
                        endX = e.getX();
                        endY = e.getY();

                        int width = startX - endX;
                        int height = startY - endY;
                        w = Math.abs(width);
                        h = Math.abs(height);

                        Rectangle r =  new Rectangle(startX, startY, w, h, pickedColor, thickness);
                        shapeList.add(r);
                        repaint(); 
                    }                    
                });   

            }
            else if (cb.getSelectedItem().equals("Circle")) {

                contentPane.addMouseListener(new MouseAdapter() {            //Second
                    @Override
                    public void mousePressed(MouseEvent e) {  
                        startX = e.getX();     
                        startY = e.getY();
                    }
                    @Override
                    public void mouseReleased(MouseEvent e) {
                        endX = e.getX();
                        endY = e.getY();

                        int width = startX - endX;
                        int height = startY - endY;
                        w = Math.abs(width);
                        h = Math.abs(height);

                        Circle c =  new Circle(startX, startY, w, h, pickedColor, thickness);

                        shapeList.add(c);
                        repaint();
                    }
                });  
            }
            else if (cb.getSelectedItem().equals("Freehand")) {   

                contentPane.addMouseListener(new MouseAdapter() {            //Third
                    @Override
                    public void mousePressed(MouseEvent e) {            
                        startX = e.getX();
                        startY = e.getY();
                    }
                    @Override
                    public void mouseDragged(MouseEvent e) {                       

                        FreeHand fh =  new FreeHand(startX, startY, e.getX(), e.getY(), pickedColor, thickness);

                        shapeList.add(fh);
                        repaint();                       
                    }
                });    
            }                    

        }

Answer 1

您应该在构造函数中向面板添加一个鼠标监听器，而不是每次在组合框中进行选择时向面板添加不同的监听器。并且此监听器在调用其方法之一时，应首先检查选择了哪个选项，并采取相应的操作(即绘制矩形或圆形，或根据选择徒手绘制)。