Java Tips - How to block mouse and key events in an application

This Java Swing tip illustrates a method of implementing blocking of mouse and key events in an applicatoin. This tip uses a glass pane for blocking the mouse and key events. This tip may be useful for developers where they want users to use the application with limited controls.

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;



public class GlassExample extends JFrame {

    

    JPanel glass = new JPanel(new GridLayout(0, 1));

    // add a label to help trap focus while the glass pane is active

    JLabel padding = new JLabel();

    JProgressBar waiter = new JProgressBar(0, 100);

    Timer timer;

    

    public GlassExample() {

        super("GlassPane Demo");

        setSize(500, 300);

        setDefaultCloseOperation(EXIT_ON_CLOSE);

        

        // Set up the glass pane with a little message and a progress bar...

        JPanel controlPane = new JPanel(new GridLayout(2,1));

        controlPane.setOpaque(false);

        controlPane.add(new JLabel("Please wait..."));

        controlPane.add(waiter);

        glass.setOpaque(false);

        glass.add(padding);

        glass.add(new JLabel());

        glass.add(controlPane);

        glass.add(new JLabel());

        glass.add(new JLabel());

        

        // trap both mouse and key events.  Could provide a smarter 

        // key handler if you wanted to allow things like a keystroke 

        // that would cancel the long-running operation.

        glass.addMouseListener(new MouseAdapter() {});

        glass.addMouseMotionListener(new MouseMotionAdapter() {});

        glass.addKeyListener(new KeyAdapter() {});

        

        // make sure the focus won't leave the glass pane

        // glass.setFocusCycleRoot(true);  // 1.4

        padding.setNextFocusableComponent(padding);  // 1.3

        setGlassPane(glass);

        

        // Now set up a few buttons & images for the main application

        JPanel mainPane = new JPanel();

        mainPane.setBackground(Color.white);

        JButton redB = new JButton("Red");

        JButton blueB = new JButton("Blue");

        JButton greenB = new JButton("Green");

        mainPane.add(redB);

        mainPane.add(greenB);

        mainPane.add(blueB);

        mainPane.add(new JLabel(new ImageIcon("java-tip.gif")));

        

        // Attach the popup debugger to the main app buttons so you

        // see the effect of making a glass pane visible

        PopupDebugger pd = new PopupDebugger(this);

        redB.addActionListener(pd);

        greenB.addActionListener(pd);

        blueB.addActionListener(pd);

        

        // And last but not least, our button to launch the glass pane

        JButton startB = new JButton("Start the big operation!");

        

        startB.addActionListener(new ActionListener() {

            public void actionPerformed(java.awt.event.ActionEvent A) {

                glass.setVisible(true);

                padding.requestFocus();  // required to trap key events

                startTimer();

            }

        });

        

        Container contentPane = getContentPane();

        contentPane.add(mainPane, BorderLayout.CENTER);

        contentPane.add(startB, BorderLayout.SOUTH);

    }

    

    // A quick method to start up a 10 second timer and update the

    // progress bar

    public void startTimer() {

        

        if (timer == null) {

            

            timer = new Timer(1000, new ActionListener() {

                

                int progress = 0;

                

                public void actionPerformed(ActionEvent A) {

                    progress += 10;

                    waiter.setValue(progress);

                    

                    // Once we hit 100%, remove the glass pane and 

                    // reset the progress bar stuff

                    if (progress >= 100) {

                        progress = 0;

                        timer.stop();

                        glass.setVisible(false);

                        waiter.setValue(0);

                    }

                }

            });

        }

        

        if (timer.isRunning()) {

            timer.stop();

        }

        

        timer.start();

    }

    

    // A graphical debugger that pops up anytime a button is pressed

    public class PopupDebugger implements ActionListener {

        

        private JFrame parent;

        

        public PopupDebugger(JFrame f) {

            parent = f;

        }

        

        public void actionPerformed(ActionEvent ae) {

            JOptionPane.showMessageDialog(parent, ae.getActionCommand());

        }

    }

    

    public static void main(String[] args) {

        GlassExample ge = new GlassExample();

        ge.setVisible(true);

    }

}
Related Tips
