java - Swing JLayeredPane 未在调用 PaintAll 时绘制所有元素

Question

我有 JLayeredPane，其中包含 0 级的 Canvas(在 Paint 方法中填充自身黄色)和 JPanel > 在第 1 级(在构造函数中将其背景设置为红色)。

在 paintAllToImage 方法中单击按钮时，我创建 BufferedImage 并使用 component.paintAll(image.getGraphics) 在此图像上绘制 JLayerePane ());
问题是，该图像仅绘制了 Canvas(它完全填充为黄色)。请参阅附图。

(按钮上面的部分是实际绘制的，按钮下面的部分是图像，从 JLayeredPane 创建)

完整代码如下:

public class LayeredPaneEx extends JPanel {

    private JLayeredPane layeredPane;
    public LayeredPaneEx()    {
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));

        layeredPane = new JLayeredPane();
        layeredPane.setPreferredSize(new Dimension(300, 310));
        layeredPane.setLayout(null);

        Canvas panel = new CustomCanvas();
        panel.setSize(300, 400);
        CustomPanel customPanel = new CustomPanel();
        layeredPane.add(panel, new Integer(0));
        layeredPane.add(customPanel, new Integer(1));

        add(layeredPane);

        JButton paintBtn = new JButton("Paint All");
        paintBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                ImageIcon icon = new ImageIcon(paintAllToImage(layeredPane));
                JLabel imageLabel = new JLabel(icon);
                add(imageLabel);
            }
        });
        add(paintBtn);

        JLabel paintLabel = new JLabel();
        paintLabel.setPreferredSize(new Dimension(300, 300));
    }

    private class CustomCanvas extends Canvas  {
        @Override
        public void paint(Graphics g) {
            g.setColor(Color.YELLOW);
            g.fillRect(0, 0, getWidth(), getHeight());
        }
    }

    private class CustomPanel extends JPanel {
        CustomPanel() {
            setSize(100, 100);
            setBackground(Color.RED);
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("LayeredPaneDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComponent newContentPane = new LayeredPaneEx();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    public static BufferedImage paintAllToImage(Component component) {
        BufferedImage image;
        image = new BufferedImage(
                component.getWidth(),
                component.getHeight(),
                BufferedImage.TYPE_INT_RGB
        );
        component.paintAll(image.getGraphics());
        return image;
    }
}

Answer 1

编辑:新答案

通过调整此Stack Overflow answer ，似乎可以将轻量级 CustomPanel 放入重量级 Panel 中，并将它们放在另一个重量级 Panel 之上。这是屏幕截图:

这是程序:

import java.awt.*;
import javax.swing.*;

/**
 * Adapted from https://stackoverflow.com/a/1428298/1694043.
 */
public class GuiTest {
    public static void main(String[] arguments) {
        new GuiTest();
    }

    public GuiTest() {
        JFrame frame = new JFrame("Heavyweight versus lightweight");
        frame.setSize(500, 500);
        frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
        addPanelsToFrame(frame);

        SwingUtilities.invokeLater(() -> frame.setVisible(true));
    }

    private void addPanelsToFrame(JFrame frame) {
        CustomCanvas customCanvas = new CustomCanvas(300, 400, Color.YELLOW);
        Panel awtPanel1 = new Panel(new BorderLayout());
        awtPanel1.setSize(300, 400);
        awtPanel1.add(customCanvas, BorderLayout.CENTER);
        frame.getLayeredPane().add(awtPanel1, JLayeredPane.DEFAULT_LAYER);

        CustomPanel customPanel = new CustomPanel(100, 100, Color.RED);
        Panel awtPanel2 = new Panel(new BorderLayout());
        awtPanel2.setSize(100, 100);
        awtPanel2.add(customPanel, BorderLayout.CENTER);
        frame.getLayeredPane().add(awtPanel2, JLayeredPane.PALETTE_LAYER);
    }


    private class CustomCanvas extends Canvas {
        private Color backgroundColor;

        public CustomCanvas(int width, int height, Color backgroundColor) {
            setSize(width, height);
            this.backgroundColor = backgroundColor;
        }

        @Override
        public void paint(Graphics g) {
            g.setColor(backgroundColor);
            g.fillRect(0, 0, getWidth(), getHeight());
        }
    }


    private class CustomPanel extends JPanel {
        public CustomPanel(int width, int height, Color backgroundColor) {
            setSize(width, height);
            setBackground(backgroundColor);
        }
    }
}

<小时/>

旧答案

使用 MadProgrammer 的建议为了避免使用 Canvas 类，您可以使用 CustomPanel 类的两个实例。该类扩展了基于 Swing 的轻量级 JPanel，而不是基于重量级 AWT 的 Canvas。请参阅https://stackoverflow.com/a/13769255/1694043有关轻量级与重量级 Java GUI 组件的更多信息。

这是屏幕截图:

修改后的代码如下:

import java.awt.*;
import java.awt.event.*;
import java.awt.image.*;
import javax.swing.*;

public class LayeredPaneEx extends JPanel {
    private JLayeredPane layeredPane;

    public LayeredPaneEx()    {
        setLayout(new BoxLayout(this, BoxLayout.PAGE_AXIS));

        layeredPane = new JLayeredPane();
        layeredPane.setPreferredSize(new Dimension(300, 310));
        layeredPane.setLayout(null);

        //Canvas panel = new CustomCanvas();
        //panel.setSize(300, 400);
        //CustomPanel customPanel = new CustomPanel();
        //layeredPane.add(panel, new Integer(0));
        //layeredPane.add(customPanel, new Integer(1));
        layeredPane.add(new CustomPanel(300, 400, Color.YELLOW), new Integer(0));
        layeredPane.add(new CustomPanel(100, 100, Color.RED), new Integer(1));

        add(layeredPane);

        JButton paintBtn = new JButton("Paint All");
        paintBtn.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                ImageIcon icon = new ImageIcon(paintAllToImage(layeredPane));
                JLabel imageLabel = new JLabel(icon);
                add(imageLabel);
            }
        });
        add(paintBtn);

        JLabel paintLabel = new JLabel();
        paintLabel.setPreferredSize(new Dimension(300, 300));
    }

//    private class CustomCanvas extends Canvas  {
//        @Override
//        public void paint(Graphics g) {
//            g.setColor(Color.YELLOW);
//            g.fillRect(0, 0, getWidth(), getHeight());
//        }
//    }

    private class CustomPanel extends JPanel {
        public CustomPanel(int width, int height, Color backgroundColor) {
            setSize(width, height);
            setBackground(backgroundColor);
        }
    }

    private static void createAndShowGUI() {
        JFrame frame = new JFrame("LayeredPaneDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JComponent newContentPane = new LayeredPaneEx();
        newContentPane.setOpaque(true);
        frame.setContentPane(newContentPane);

        frame.pack();
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }

    public BufferedImage paintAllToImage(Component component) {
        BufferedImage image = new BufferedImage(
                component.getWidth(),
                component.getHeight(),
                BufferedImage.TYPE_INT_RGB
        );
        component.paintAll(image.getGraphics());

        return image;
    }
}