java - 当我释放鼠标按钮时，MouseEvent未注册发布

public void mousePressed(MouseEvent e) {
    //Invoked when a mouse button has been pressed on a component.
    if (e.getButton() == MouseEvent.BUTTON1) {
        isDown = true;
        System.out.println("isDown is now true");
    }
    if (e.getButton() == MouseEvent.BUTTON3) {
        isDown2 = true;
        System.out.println("isDown2 is now true");
    }
    do {
        Point location = MouseInfo.getPointerInfo().getLocation();
        int x = location.x - (drawingPanel.getLocationOnScreen()).x;
        int y = location.y - (drawingPanel.getLocationOnScreen()).y;
        drawingPanel.paint(drawingPanel.getGraphics(), (x - (x % 20) - 1), (y - (y % 20) - 1), 19, 19);
    } while (isDown);
    System.out.println("Mouse has been pressed down.");
}

public void mouseReleased(MouseEvent e) {
    //Invoked when a mouse button has been released on a component.
    if (e.getButton() == MouseEvent.BUTTON1) {
        isDown = false;
        System.out.println("isDown is now false");
    }
    if (e.getButton() == MouseEvent.BUTTON3) {
        isDown2 = false;
        System.out.println("isDown2 is now false");
    }
    System.out.println("Mouse has been released.");
}

这是我到目前为止所拥有的。我的初衷是设计代码，以便在按下鼠标时将布尔值isDown设置为true，然后在while为true时运行isDown循环。如果释放鼠标按钮，则我将isDown设置为false，以终止while循环。

我在这里搞砸了吗？两个MouseEvent方法不能同时运行吗？ isDown布尔变量中的更改未注册，并且我的手上有一个无限的while循环。

最佳答案

这是对事件调度线程的经典违反。

所有UI代码都在单个线程中运行。所有事件都是从同一线程分派UI的，这意味着如果您阻塞该线程（使用循环或其他阻塞操作），则不会分派任何事件。这将使您的程序看起来已挂起。

有关更多详细信息，请参见Concurrency in Swing。

您真正应该做的是改为使用MouseMoitionListener跟踪拖动事件。查看How to use Mouse Listeners以获得更多详细信息。

这drawingPanel.paint(drawingPanel.getGraphics(), (x - (x % 20) - 1), (y - (y % 20) - 1), 19, 19);也让我无休止。

您永远不要使用getGraphics来执行自定义绘制。 getGraphics可以返回null，它只是最后一个绘制周期的快照。使用其他方法重新绘制时，使用此方法完成的任何绘制都将被删除/清除。

您应该创建一个自定义组件（例如JPanel）并覆盖它的paintComponent方法，并在其中进行所需的绘制。查看Performing Custom Painting了解更多详细信息

例

public class MouseDraggedTest {

    public static void main(String[] args) {
        new MouseDraggedTest();
    }

    public MouseDraggedTest() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (Exception ex) {
                }

                JFrame frame = new JFrame("Test");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private Map<Point, List<Point>> mapPoints;
        private Point currentPoint;

        public TestPane() {
            mapPoints = new HashMap<>(25);
            MouseAdapter mouseListener = new MouseAdapter() {
                @Override
                public void mousePressed(MouseEvent e) {
                    currentPoint = e.getPoint();
                    mapPoints.put(currentPoint, new ArrayList<Point>(25));
                }

                @Override
                public void mouseReleased(MouseEvent e) {
                    List<Point> points = mapPoints.get(currentPoint);
                    if (points.isEmpty()) {
                        mapPoints.remove(currentPoint);
                    }
                    currentPoint = null;
                }

                @Override
                public void mouseDragged(MouseEvent me) {
                    List<Point> points = mapPoints.get(currentPoint);
                    points.add(me.getPoint());
                    repaint();
                }
            };
            addMouseListener(mouseListener);
            addMouseMotionListener(mouseListener);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);

            for (Point startPoint : mapPoints.keySet()) {
                List<Point> points = mapPoints.get(startPoint);
                for (Point p : points) {
                    if (startPoint != null) {
                        g.drawLine(startPoint.x, startPoint.y, p.x, p.y);
                    }
                    startPoint = p;
                }
            }
        }
    }
}

关于java - 当我释放鼠标按钮时，MouseEvent未注册发布，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/14764157/