java如何使用图像填充边框布局制作JLabel。居中

Question

我得到了一个JFrame并将LayoutManager设置为BorderLayout，然后继续添加带有图像的JLabel。但是，当我调整帧的大小时，JLabel不会调整大小。我没有向North、S、E等添加任何组件。我只是希望标签里的图像能填满整个画面，当然，我的菜单也能保持原样

Answer 1

如果这看起来很傲慢，请原谅我，但我没有别的事要说

我做了一个快速样品

请参见图像周围的红线，这是JLabel的边界。如您所见，标签已重新调整大小以填充整个区域

这是我用来生成示例的代码

public class LayoutFrame extends JFrame {

    public LayoutFrame() throws HeadlessException {

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        Image image = null;
        URL url = getClass().getResource("/layout/issue78.jpg");
        try {
            image = ImageIO.read(url);
        } catch (IOException ex) {

            ex.printStackTrace();

        }

        JLabel label = new JLabel(new ImageIcon(image));
        label.setHorizontalAlignment(JLabel.CENTER);
        label.setVerticalAlignment(JLabel.CENTER);
        label.setBorder(new LineBorder(Color.RED, 4));

        setLayout(new BorderLayout());

        add(label);

    }

    public static void main(String[] args) {

        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {

                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                LayoutFrame frame = new LayoutFrame();
                frame.setSize(200, 200);
                frame.setLocationByPlatform(true);
                frame.setVisible(true);

            }
        });

    }

}

显然，您需要提供自己的映像；）

别忘了，标签不会为您扩展内容，如果这是您的目标，您需要实现自己的组件来实现这一点

如果您仍然有问题，我建议（在没有进一步证据的情况下）您的标签可能不在您认为的容器中，或者容器布局管理器不是您认为的那样

更新

我不知道您为什么会遇到组件丢失或菜单问题。是否混合了重量重和重量轻的成分

带有菜单栏的示例

在仔细阅读您的问题之后，我设计了一个简单的调整图像窗格大小的示例。为了提高速度，我依赖于我的库，但是实现自己的代码来代替我的调用应该相当容易

public class ImagePane extends JPanel {

    protected static final Object RESIZE_LOCK = new Object();

    private BufferedImage image;
    private BufferedImage scaledImage;
    private Timer resizeTimer;

    public ImagePane() {

        URL url = getClass().getResource("/layout/issue78.jpg");
        try {
            image = ImageIO.read(url);
        } catch (IOException ex) {

            ex.printStackTrace();

        }

        resizeTimer = new Timer(250, new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {

                // Simple thread factory to start a slightly lower 
                // priority thread.
                CoreThreadFactory.getUIInstance().execute(new ResizeTask());

            }

        });

        resizeTimer.setCoalesce(true);
        resizeTimer.setRepeats(false);

    }

    @Override
    public void setBounds(int x, int y, int width, int height) {

        super.setBounds(x, y, width, height);

        resizeTimer.restart();

    }

    @Override
    protected void paintComponent(Graphics g) {

        super.paintComponent(g);

        Graphics2D g2d = (Graphics2D) g;
        if (scaledImage != null) {

            // This simply returns a rectangle that takes into consideration
            //the containers insets
            Rectangle safeBounds = UIUtilities.getSafeBounds(this);

            System.out.println("scaledImage = " + scaledImage.getWidth() + "x" + scaledImage.getWidth());

            int x = ((safeBounds.width - scaledImage.getWidth()) / 2) + safeBounds.x;
            int y = ((safeBounds.height - scaledImage.getHeight()) / 2) + safeBounds.y;

            g2d.drawImage(scaledImage, x, y, this);

        }

    }

    protected class ResizeTask implements Runnable {

        @Override
        public void run() {

            synchronized (RESIZE_LOCK) {

                if (image != null) {

                    int width = getWidth();
                    int height = getHeight();

                    System.out.println("width = " + width);
                    System.out.println("height = " + height);

                    // A simple divide and conquer resize implementation
                    // this will scale the image so that it will fit within
                    // the supplied bounds
                    scaledImage = ImageUtilities.getScaledInstanceToFit(image, new Dimension(width, height), ImageUtilities.RenderQuality.High);

                    System.out.println("scaledImage = " + scaledImage.getWidth() + "x" + scaledImage.getWidth());

                    repaint(); // this is one of the few thread safe calls

                }

            }

        }

    }

}

Answer 2

最好的选择是对ImageIcon进行子类化，并覆盖其paintIcon方法，以便使用图形简单地绘制图像。油漆（x、y、宽度、高度…）