Question

Code in Question:

    textArea.addMouseListener(new MouseAdapter() {
        public void mousePressed(MouseEvent e) {
            posX = e.getX();
            posY = e.getY();
        }
    });
    textArea.addMouseMotionListener(new MouseAdapter() {
        public void mouseDragged(MouseEvent e) {
            setLocation(e.getXOnScreen() - posX, e.getYOnScreen() - posY);
        }
    });

Background:

I have a JFrame, in that JFrame there is a JScrollPane, and in the JScrollPane there is a JTextArea called “textArea”. This JTextArea take up the entire JFrame and the JFrame is undecorated. So to give some perspective, here is generally what the JFrame looks like…

When the mouse clicks within the JTextArea and moves, the entire window is dragged. Everything is setup to not be focus able for this work, it’s meant to be an overlay.

Issue:

The code listed above works fine and the world is at peace. But once there is enough text for the vertical scroll bar to appear (There is no horizontal because of line wrapping), dragging the window becomes an issue. When you click and just begin to move, the JFrame instantly moves much higher on the screen. The lines in JTextArea, the higher it moves up when you try to move it. I assume that the get*OnScreen() methods are issue because it’s all relevant to the JTextArea.

Class in Question:

import java.awt.Color;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Main extends JFrame {
    private JTextArea textArea;
    private JScrollPane textAreaScroll;
    private int posX = 0;
    private int posY = 0;

public Main() {
    initComponents();
    initListeners();
    for(int i = 0; i < 20; i++){
        addLine(i+" Hello");            
    }
}

public void addLine(String line){
    textArea.append("\n> "+line);
    textArea.setCaretPosition(textArea.getDocument().getLength());
}

private void initListeners(){
    textArea.addMouseListener(new MouseAdapter() {
        public void mousePressed(MouseEvent e) {
            posX = e.getX();
            posY = e.getY();
        }
    });
    textArea.addMouseMotionListener(new MouseAdapter() {
        public void mouseDragged(MouseEvent e) {
            setLocation(e.getXOnScreen() - posX, e.getYOnScreen() - posY);
        }
    });
}

private void initComponents() {
    try {
        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
    } catch (UnsupportedLookAndFeelException | ClassNotFoundException | InstantiationException | IllegalAccessException e) {}

    textAreaScroll = new JScrollPane();
    textArea = new JTextArea();

    setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
    setUndecorated(true);
    setAlwaysOnTop(true);
    setAutoRequestFocus(false);
    setBackground(new Color(130,210,255,130));
    setFocusCycleRoot(false);
    setFocusable(false);
    setFocusableWindowState(false);
    setName("main");
    setOpacity(0.4f);
    setResizable(false);

    textAreaScroll.setBorder(null);
    textAreaScroll.setFocusable(false);
    textAreaScroll.setRequestFocusEnabled(false);

    textArea.setEditable(false);
    textArea.setBackground(new Color(0, 0, 0));
    textArea.setColumns(20);
    textArea.setFont(new Font("Consolas", 0, 14));
    textArea.setForeground(new Color(255, 255, 255));
    textArea.setLineWrap(true);
    textArea.setRows(5);
    textArea.setText("> Hello world!\n> another line!");
    textArea.setBorder(null);
    textArea.setFocusable(false);
    textArea.setRequestFocusEnabled(false);
    textAreaScroll.setViewportView(textArea);

    javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
    getContentPane().setLayout(layout);
    layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(textAreaScroll, javax.swing.GroupLayout.DEFAULT_SIZE, 400, Short.MAX_VALUE)
            );
    layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addComponent(textAreaScroll, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 214, Short.MAX_VALUE)
            );

    pack();
}

public static void main(String args[]) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            new Main().setVisible(true);
        }
    });
}

}

Answer 1

Well your diagnosis was absolutely spot on:

When you click and just begin to move, the JFrame instantly moves
much higher on the screen. The lines in JTextArea, the higher it moves
up when you try to move it. I assume that the get*OnScreen() methods
are issue because it’s all relevant to the JTextArea.

So to resolve this use GlassPane of JFrame to attach MouseXXXListeners thus we can get correct co-ordinates when dragging, the main problem with this solution is glasspane will consume events that are meant for other components on JFrame, this can be overcome by redispatching the MouseEvents appropriately):

• Create JPanel (this glassPane/JPanel will be transparent via setOpaque(false)), attach xxxAdapters here.

• Create custom listener class to redispacth MouseEvents to the necessary components (as glasspane will consume all events to the JTextArea/JScollPane)

• Set JPanel as GlassPane of your JFrame via JFrame#setGlassPane(..) .

• set JFrame visible than set glassPane visible via setVisible(true) (this has been a Swing glitch for some time if you set it visible before the frame is visible it wont be shown).

Here is your fixed code:

import java.awt.Color;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Font;
import java.awt.Point;
import java.awt.Toolkit;
import java.awt.event.MouseEvent;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextArea;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.MouseInputAdapter;

public class Main extends JFrame {

    private JTextArea textArea;
    private JScrollPane textAreaScroll;
    private JPanel glassPane;//create variable for glasspane

    public Main() {
        initComponents();
        initListeners();
        for (int i = 0; i < 20; i++) {
            addLine(i + " Hello");
        }
    }

    public void addLine(String line) {
        textArea.append("\n> " + line);
        textArea.setCaretPosition(textArea.getDocument().getLength());
    }

    private void initListeners() {
        GlassPaneListener gpl = new GlassPaneListener(textAreaScroll.getVerticalScrollBar(), this);
        //add the adapters/listeners to the glasspane
        glassPane.addMouseMotionListener(gpl);
        glassPane.addMouseListener(gpl);
    }

    private void initComponents() {
        try {
            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
        } catch (UnsupportedLookAndFeelException | ClassNotFoundException | InstantiationException | IllegalAccessException e) {
        }

        textAreaScroll = new JScrollPane();
        textArea = new JTextArea();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setUndecorated(true);
        setAlwaysOnTop(true);
        setAutoRequestFocus(false);
        setBackground(new Color(130, 210, 255, 130));
        setFocusCycleRoot(false);
        setFocusable(false);
        setFocusableWindowState(false);
        setName("main");
        setOpacity(0.4f);
        setResizable(false);

        textAreaScroll.setBorder(null);
        textAreaScroll.setFocusable(false);
        textAreaScroll.setRequestFocusEnabled(false);

        textArea.setEditable(false);
        textArea.setBackground(new Color(0, 0, 0));
        textArea.setColumns(20);
        textArea.setFont(new Font("Consolas", 0, 14));
        textArea.setForeground(new Color(255, 255, 255));
        textArea.setLineWrap(true);
        textArea.setRows(5);
        textArea.setText("> Hello world!\n> another line!");
        textArea.setBorder(null);
        textArea.setFocusable(false);
        textArea.setRequestFocusEnabled(false);
        textAreaScroll.setViewportView(textArea);
        textAreaScroll.setPreferredSize(new Dimension(200, 200));

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(textAreaScroll, javax.swing.GroupLayout.DEFAULT_SIZE, 400, Short.MAX_VALUE));
        layout.setVerticalGroup(
                layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
                .addComponent(textAreaScroll, javax.swing.GroupLayout.Alignment.TRAILING, javax.swing.GroupLayout.DEFAULT_SIZE, 214, Short.MAX_VALUE));

        //create and make glasspane not opaque
        glassPane = new JPanel();
        glassPane.setOpaque(false);

        //set glasspane as JFrame glassPane
        setGlassPane(glassPane);

        pack();

        setVisible(true);//set JFrame visible

        //glassPane can only be setVisible after JFrame is visible
        glassPane.setVisible(true);
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Main();
            }
        });
    }
}

class GlassPaneListener extends MouseInputAdapter {

    private int posX = 0;
    private int posY = 0;
    Toolkit toolkit;
    private final Container contentPane;
    private final Component textAreaScroll;
    private final Component glassPane;
    private final JFrame frame;
    private boolean wasClickOnInterestedComponent = false;

    public GlassPaneListener(Component textAreaScroll, JFrame frame) {
        toolkit = Toolkit.getDefaultToolkit();
        this.textAreaScroll = textAreaScroll;
        this.frame = frame;
        this.glassPane = frame.getGlassPane();
        this.contentPane = frame.getContentPane();
    }

    @Override
    public void mouseDragged(MouseEvent e) {
        if (!redispatchMouseEvent(e)) {
            frame.setLocation(e.getXOnScreen() - posX, e.getYOnScreen() - posY);
        }
    }

    @Override
    public void mousePressed(MouseEvent e) {
        if (!redispatchMouseEvent(e)) {//check if event was redispatched if not its meant for us :)
            posX = e.getX();
            posY = e.getY();
        }
    }

    @Override
    public void mouseReleased(MouseEvent me) {
        wasClickOnInterestedComponent = false;
    }

    private boolean redispatchMouseEvent(MouseEvent e) {
        Point glassPanePoint = e.getPoint();
        Container container = contentPane;
        Point containerPoint = SwingUtilities.convertPoint(glassPane, glassPanePoint, contentPane);

        // The mouse event is probably over the content pane.
        // Find out exactly which component it's over.
        Component component = SwingUtilities.getDeepestComponentAt(container, containerPoint.x,
                containerPoint.y);

        if ((component != null) && (component.equals(textAreaScroll)) || wasClickOnInterestedComponent) {
            wasClickOnInterestedComponent = true;//so that if we drag iur cursor off JScrollBar tghe window wont be moved
            // Forward events over the scrollbar
            Point componentPoint = SwingUtilities.convertPoint(glassPane, glassPanePoint, component);
            component.dispatchEvent(new MouseEvent(component, e.getID(), e.getWhen(), e.getModifiers(),
                    componentPoint.x, componentPoint.y, e.getClickCount(), e.isPopupTrigger()));
            return true;//the event was redispatched
        } else {
            return false;//event was not redispatched
        }
    }
}