Attaching A Single Action Listener To All Buttons

Question

I have a program with many buttons, all of which will be performing the same function. I was wondering if there was a way to attach a single listener to all existing JButtons in the program.

Answer 1

Something like:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;

public class CalculatorPanel extends JPanel
{
    private JTextField display;

    public CalculatorPanel()
    {
        Action numberAction = new AbstractAction()
        {
            @Override
            public void actionPerformed(ActionEvent e)
            {
                display.setCaretPosition( display.getDocument().getLength() );
                display.replaceSelection(e.getActionCommand());
            }
        };

        setLayout( new BorderLayout() );

        display = new JTextField();
        display.setEditable( false );
        display.setHorizontalAlignment(JTextField.RIGHT);
        add(display, BorderLayout.NORTH);

        JPanel buttonPanel = new JPanel();
        buttonPanel.setLayout( new GridLayout(0, 5) );
        add(buttonPanel, BorderLayout.CENTER);

        for (int i = 0; i < 10; i++)
        {
            String text = String.valueOf(i);
            JButton button = new JButton( text );
            button.addActionListener( numberAction );
            button.setBorder( new LineBorder(Color.BLACK) );
            button.setPreferredSize( new Dimension(50, 50) );
            buttonPanel.add( button );

            KeyStroke pressed = KeyStroke.getKeyStroke(text);
            InputMap inputMap = button.getInputMap(JComponent.WHEN_IN_FOCUSED_WINDOW);
            inputMap.put(pressed, text);
            button.getActionMap().put(text, numberAction);
        }
    }

    private static void createAndShowUI()
    {
//      UIManager.put("Button.margin", new Insets(10, 10, 10, 10) );

        JFrame frame = new JFrame("Calculator Panel");
        frame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        frame.add( new CalculatorPanel() );
        frame.pack();
        frame.setLocationRelativeTo( null );
        frame.setVisible(true);
    }

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

The Action will get the source object from the Event so that it knows which button was clicked.

If you need to use if/else logic in your Action, then you should be creating a separate Action. Don't force code into one Action if it doesn't belong.

Answer 2

Simply add the ActionListener to the buttons.

For the specific action depending on the source, you can use what I wrote or use ActionCommands (which basically links certain components to 'commands' that are sent to the ActionListener on an event).

Here's a little example:

public class MyClass implements ActionListener
{
    JButton button1;
    JButton button2;
    JButton button3;

    public MyClass()
    {
        button1 = new JButton();
        button2 = new JButton();
        button3 = new JButton();

        button1.addActionListener(this);
        button2.addActionListener(this);
        button3.addActionListener(this);
    }

    @Override
    public void ActionPerformed(ActionEvent e)
    {
        //do stuff

        //if you want to do something depending on the button pressed
        //check the source
        if (e.getSource() == button1)
        {
            //do stuff
        }
    }

}

Answer 3

You Could...

Create a single instance of the ActionListner and apply it to all the buttons

You Could...

Make use if the Actions API, which will allow you to create a self contained ActionListerner, which also includes the details to configure the buttons as well.

Answer 4

There are many ways to do it.

Do you control creation of these buttons? If yes, create a factory and attach a listener before returning the object

Otherwise, you may traverse swing tree and check for instance of JButton and attach on a match

You can also think about ActionMap/InputMap approach where an action can be stored and invoked based on the focus policy.

Also, you may extend JButton....