Question

I am trying to extend the StyledEditorKit in Swing to be able to include a JLabel inside the editor. I was able to do that and this is what I got so far. In the image below, the highlighted text button is of type JLabel whereas the rest of the text is normal text.

As you can see the label renders a little below than the normal text. How do I align its top with top of the remaining text?

Here is the code for the view that is used to create this label element:

class ComponentView(Element elem) {
      @Override
      protected Component createComponent() {
        JLabel lbl = new JLabel("");
        lbl.setOpaque(true);
        lbl.setBackground(Color.red);
        try {
               int start = getElement().getStartOffset();
               int end = getElement().getEndOffset();
               String text = getElement().getDocument().getText(start, end - start);
               lbl.setText(text);
         } catch (BadLocationException e) {}
         return lbl;
       }
}

Answer 1

Try adjusting Component.getAlignmentY that controls the positioning of component relative to the text baseline as suggested in ComponentView.

You could also try using JTextPane that provides easier support for embedded components. Components can be added using insertComponent() method. Here is an example, it also demos setAlignmentY:

import java.awt.BorderLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextPane;
import javax.swing.SwingUtilities;

public class TextPaneDemo {
    private static void createAndShowGUI() {
        final JTextPane pane = new JTextPane();
        pane.setText("Some text");

        JButton buttonButton = new JButton("Insert label");
        buttonButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent event) {
                JLabel label = new JLabel("label");
                label.setAlignmentY(0.85f);
                pane.insertComponent(label);
            }
        });

        JPanel panel = new JPanel(new BorderLayout());
        panel.add(buttonButton, BorderLayout.SOUTH);
        panel.add(pane, BorderLayout.CENTER);

        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(panel);
        frame.setSize(400, 200);
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

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