java - 当我拖动它时，swing 中的可拖动圆圈会闪烁

Question

我正在实现一个 Swing 程序，它将形状绘制到屏幕上，然后让用户拖动它们。我可以很好地绘制一个形状，但是一旦我单击一个形状来拖动它，该形状就会在拖动时开始闪烁。

这是我的 GUI 类和 MouseAdapter 类:

public class GUI extends JFrame {
    private JMenu addShapeMenu = new JMenu("Add Shape");
    private JLabel statusBar = new JLabel();
    private List<Shape> _shapes;
    private Shape chosenShape;
    private boolean isShapeClicked = false;
    private List<String> shapeSubclasses = new ArrayList<>();

    public GUI() throws IOException, ClassNotFoundException, IllegalAccessException, InstantiationException {
        super("DrawingBoard");
        setSize(500, 500);
        setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);

        JMenuBar menuBar = new JMenuBar();
        setJMenuBar(menuBar);
        menuBar.add(addShapeMenu);

        getContentPane().setLayout(new BorderLayout());

        getLoadedShapes();
        for(String shape : shapeSubclasses)
        {
            Class drawableShape = Class.forName("gui.Drawable" + shape);
            addShapeMenu.add(((DrawableShape)drawableShape.newInstance()).getInstance().getMenuItem());
        }

        add(statusBar, BorderLayout.SOUTH);
        statusBar.setText("Add a shape.");

        MouseHandler mouseHandler = new MouseHandler();
        addMouseListener(mouseHandler);
        addMouseMotionListener(mouseHandler);

        setVisible(true);
    }

    public void paint(Graphics graphics)
    {
        super.paint(graphics);
        for(Shape shape : _shapes)
        try
        {
            Class painter = Class.forName("gui.Drawable" + shape.getClass().getSimpleName());
            ((DrawableShape)painter.newInstance()).getInstance().paint(getGraphics(), shape);
        }

        catch(Exception e)
        {
            JOptionPane.showMessageDialog(this, "Failed to load Drawable" + shape);
        }
    }

    private class MouseHandler extends MouseAdapter implements MouseMotionListener {
        public void mousePressed(MouseEvent event) {
            _shapes.forEach(shape -> {
                if(shape.isPointInside(event.getX(), event.getY()))
                    chosenShape = shape;
                isShapeClicked = true;
            });
        }

        public void mouseDragged(MouseEvent event) {
            if (isShapeClicked) {
                chosenShape.moveTo(event.getX(), event.getY());
                repaint();
            }
        }

        public void mouseReleased(MouseEvent event) {
            isShapeClicked = false;
                chosenShape = null;
        }
    }
}

我的 DrawableCircle 类有一个方法 Paint:

public void paint(Graphics graphics, Shape shape)
    {
        int radius = ((Circle)shape).getRadius();
        graphics.fillOval(shape.getX() - radius, shape.getY() - radius, radius * 2, radius * 2);
    }

DrawRectangle 类类似。

Answer 1

• 正在 paint 中加载类方法不是一个好主意，因为这可能会花费宝贵的时间，从而可能导致屏幕更新延迟
• 不要覆盖paint顶级容器的，它们不是双缓冲的。相反，创建一个自定义组件，从类似 JPanel 扩展而来。并覆盖它的 paintComponent方法，将您的自定义绘画放入 to (不要忘记先调用 super.paintComponent)。

参见Performing Custom Painting和 Painting in AWT and Swing了解更多详情