JLayeredPane not adding a view on top

Question

Trying to create a translucent paint view over my application.

So far, I have a few objects at play.

paintView //a wrapper class of a JPane.
gScrollPane // the area I'm trying to cover
layeredPane // the layered pane

Here's my code so far

layeredPane = new JLayeredPane();
paintView = new PaintView//rest of constructor
layeredPane.add(gScrollPane);
layeredPane.add(paintView.getComponent(), new Integer(5));
layeredPane.moveToFront(paintView.getComponent());

For some reason, it's just not working. getComponent returns a jPane. So that shouldn't be the issue. I've made the panel red and opaque for testing but no luck. Have I missed something in the documentation?

Edit:

So I'm not seeing the paintview on top of the gScrollPane

and getComponent just returns the internally wrapped pane. That's not really the issue though.

I think it has to do with the layout of the layered pane. (Flow at the moment) Setting to box has the layers horizontally side by side (paintview left, gscrollpane right)

Answer 1

It's difficult to know exactly why you're having problems. It could be a paint issue, it could be a layout issue...

Don't forget, JLayeredPane has not layout manager by default. You could use one, but I simply overrode the doLayout method and "implemented" my own for the purpose of the example...

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Component;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FontMetrics;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Image;
import java.awt.Rectangle;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.io.Reader;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JLayeredPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.BadLocationException;
import javax.swing.text.Element;

public class TestLayeredPane02 {

    public static void main(String[] args) {
        new TestLayeredPane02();
    }

    public TestLayeredPane02() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestPane());
                frame.setSize(600, 400);
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JLayeredPane {

        private JTextPane tp;

        public TestPane() {
            tp = new JTextPane();

            Reader reader = null;
            try {
                reader = new FileReader(new File("sometextfile.txt"));
                tp.read(reader, "Help");
            } catch (Exception e) {
                e.printStackTrace();
            } finally {
                try {
                    reader.close();
                } catch (Exception e) {
                }
            }
            tp.setFont(UIManager.getFont("TextArea.font"));

            JScrollPane scrollPane = new JScrollPane(tp);
            scrollPane.setRowHeaderView(new LineNumberHeader(tp));

            OverLayPane overLayPane = new OverLayPane();

            add(scrollPane, new Integer(0));
            add(overLayPane, new Integer(5));

            moveToFront(overLayPane);
        }

        @Override
        public void doLayout() {
            for (Component comp : getComponents()) {
                comp.setBounds(0, 0, getWidth(), getHeight());
            }
        }

    }

    public class OverLayPane extends JPanel {

        public OverLayPane() {
            setLayout(new BorderLayout());
            try {
                BufferedImage img = ImageIO.read(new File("/path/to/image.png"));
                JLabel label = new JLabel(new ImageIcon(img.getScaledInstance(-1, 200, Image.SCALE_SMOOTH)));
                label.setHorizontalAlignment(JLabel.CENTER);
                label.setVerticalAlignment(JLabel.CENTER);
                add(label);
            } catch (IOException ex) {
                ex.printStackTrace();
            }
            setOpaque(false);
            setBackground(new Color(255, 0, 0, 128));
        }

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

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();
            g2d.setColor(getBackground());
            g2d.fill(new Rectangle(0, 0, getWidth(), getHeight()));
            g2d.dispose();
        }
    }
    public class LineNumberHeader extends JPanel {

        private JTextPane field;

        public LineNumberHeader(JTextPane field) {
            this.field = field;
            field.getDocument().addDocumentListener(new DocumentListener() {

                @Override
                public void insertUpdate(DocumentEvent e) {
                    revalidate();
                    repaint();
                }

                @Override
                public void removeUpdate(DocumentEvent e) {
                    revalidate();
                    repaint();
                }

                @Override
                public void changedUpdate(DocumentEvent e) {
                    revalidate();
                    repaint();
                }

            });
        }

        @Override
        public Dimension getPreferredSize() {
            int height = field.getPreferredSize().height;
            Element root = field.getDocument().getDefaultRootElement();
            int lineCount = root.getElementCount();
            FontMetrics fm = getFontMetrics(getFont());
            int width = fm.stringWidth(Integer.toString(lineCount)) + 4;
            return new Dimension(width, height);
        }

        protected void drawLineNumber(Graphics2D g2d, int line, Element element) {
            int startIndex = element.getStartOffset();
            FontMetrics fm = g2d.getFontMetrics();
            String strLine = Integer.toString(line);
            try {
                Rectangle rect = field.modelToView(startIndex);
                int strWidth = fm.stringWidth(strLine);
                g2d.drawString(strLine, getWidth() - 2 - strWidth, rect.y + fm.getAscent());
            } catch (BadLocationException ex) {
                ex.printStackTrace();
            }
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g.create();

            Element root = field.getDocument().getDefaultRootElement();
            drawLineNumber(g2d, 1, root);
            for (int index = 0; index < root.getElementCount(); index++) {
                Element element = root.getElement(index);
                drawLineNumber(g2d, index + 1, element);
            }
            g2d.dispose();
        }
    }        
}