未选择单选按钮时调用ActionEvent

Question

I've noticed that ActionEvent would still be triggered within my group of JRadioButtonMenuItem even when specifying the conditional statement:

if(!button.isSelected())
    //Do stuff

---

defaultTheme = new JRadioButtonMenuItem("Default theme");
    defaultTheme.addActionListener(new ActionListener() {
        @Override
        public void actionPerformed(ActionEvent e) {
            if(!defaultTheme.isSelected())  
                System.out.println("temp");
        }
    });

---

I have multiple theme options within my settings menu, however if a say (say default) is already selected, I don't want to execute any redundant code if the default menu is already selected and the user clicks on the already selected Radio Button.

Answer 1

ActionListener will tell you whenever the button is "actioned" (clicked, pressed, what ever), which doesn't always change it's state. Instead, you could attach a ItemListener to the buttons model, which will tell, more accurately, when the actual state of the button changes, for example...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.ItemEvent;
import java.awt.event.ItemListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class ButtonTest {

    public static void main(String[] args) {
        new ButtonTest();
    }

    public ButtonTest() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                    ex.printStackTrace();
                }

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new TestPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setLayout(new GridBagLayout());
            GridBagConstraints gbc = new GridBagConstraints();
            gbc.gridwidth = GridBagConstraints.REMAINDER;

            ButtonGroup bg = new ButtonGroup();
            final JRadioButton bananas = new JRadioButton("Bananas");
            final JRadioButton apples = new JRadioButton("Apples");
            bg.add(bananas);
            bg.add(apples);

            bananas.getModel().addItemListener(new ItemListener() {
                @Override
                public void itemStateChanged(ItemEvent e) {
                    System.out.println("Bananas " + bananas.isSelected());
                }
            });
            apples.getModel().addItemListener(new ItemListener() {
                @Override
                public void itemStateChanged(ItemEvent e) {
                    System.out.println("Apples " + apples.isSelected());
                }
            });

            add(bananas, gbc);
            add(apples, gbc);

        }

    }

}

Answer 2

Not sure since I haven't seen the rest of your program, but you have to put all the radiobuttons in a ButtonGroup. Because if you don't it would be impossible to deselect the radiobutton.