Java Swing JTextArea Line number

问题

This count line number of textarea. The code works correctly, but when run this code the textarea is not active, the caret is hidden and the keyboard
keys not work unless I click on textarea.

code:

import java.awt.BorderLayout;
import java.awt.Color;

import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.event.DocumentEvent;
import javax.swing.event.DocumentListener;
import javax.swing.text.Element;

public class LineNumber extends JFrame implements DocumentListener {

    private static final long serialVersionUID = -1093726028044203117L;

    private JScrollPane scroll;
    private JTextArea textArea, lineArea;

    public static void main(String[] args) {

        new LineNumber().setVisible(true);

    }

    public LineNumber() {

        super("Line Numbers");

        setSize(500, 500);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        setUI();
    }

    private void setUI() {

        textArea = new JTextArea();

        lineArea = new JTextArea(0, 3);
        lineArea.setEditable(false);
        lineArea.setForeground(Color.GRAY);

        scroll = new JScrollPane(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

        textArea.getDocument().addDocumentListener(this);

        scroll.setViewportView(textArea);
        scroll.setRowHeaderView(lineArea);
        getContentPane().add(scroll, BorderLayout.CENTER);

    }

    public void changedUpdate(DocumentEvent event) {

        lineArea.setFont(textArea.getFont());
        lineArea.setText(getLine());

    }

    public void insertUpdate(DocumentEvent event) {

        lineArea.setFont(textArea.getFont());
        lineArea.setText(getLine());
    }

    public void removeUpdate(DocumentEvent event) {

        lineArea.setFont(textArea.getFont());
        lineArea.setText(getLine());
    }

    public String getLine() {

        int caretPos = 0;
        String lines;

        caretPos = textArea.getDocument().getLength();
        Element root = textArea.getDocument().getDefaultRootElement();
        lines = String.format("%s%s", 1, System.lineSeparator());

        for (int i = 2; i < root.getElementIndex(caretPos) + 2; i++) {
            lines += String.format("%s%s", i, System.lineSeparator());

        }

        return lines;

    }

}

If I do not add lineArea to the scrollpane the textarea work correctly but after add to setRowHeaderView the textarea only gets active with a mouse click....

回答1:

You can prevent the line number text area from gaining focus by using:

lineArea = new JTextArea(0, 3);
lineArea.setEditable(false);
lineArea.setFocusable(false);

You can also check out Text Component Line Number for a fancier implementation that supports:

wrapped text
text with different size fonts (when using a JTextPane)

回答2:

By default it focus on first component, so if you want to focus on another one try this code in the constructor.

addWindowFocusListener(new WindowAdapter() {
    @Override
    public void windowGainedFocus(WindowEvent e) {
        textArea.requestFocusInWindow();
    }
});

textArea is now focused, more on this.

来源：https://stackoverflow.com/questions/52179097/java-swing-jtextarea-line-number

标签

java

swing

jscrollpane

jtextarea

caret