Swing: Intercept click on a JRadiobutton-CodePudding

I want to intercept the click on a JRadioButton in a button group. More precise: When JRadioButton A is chosen and the user clicks on JRadioButton B, I want to show a Yes/No-option pane. Only when the user clicks "Yes", radio button B be will be selected. If the user clicks on "No" nothing is supposed to change. Is this or rather how is this possible?

Thanks for your time

CodePudding user response：

You want to listen for ItemEvents to know when the first button is selected (see this). You can use AbstractButton#isSelected to check that the other button is selected. Finally, you can use JOptionPane#showConfirmDialog(Component, Object, String, int) to prompt the user for "Yes" or "No," and use something like AbstractButton#setSelected(boolean) or ButtonGroup#clearSelection to control which buttons are selected.

This should get you started down the right tract.

CodePudding user response：

Add an ItemListener to the B radio button. Refer to How to Use Radio Buttons. The listener is invoked after the selection has changed.

If the B button is selected, display a JOptionPane asking the user to confirm. Refer to How to Make Dialogs. A JOptionPane can also be closed by hitting the ESC key or pressing the X button in the top, right corner.

If the user closes the JOptionPane by clicking the YES button, we do nothing since button B is actually already selected. If the user closes the JOptionPane any other way, then we need to reset the selection to button A.

import java.awt.EventQueue;
import java.awt.event.ItemEvent;

import javax.swing.ButtonGroup;
import javax.swing.JFrame;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;

public class Intercep {
    private JFrame frame;
    private JRadioButton aRadioButton;
    private JRadioButton bRadioButton;

    private void buildAndDisplayGui() {
        frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.add(createButtons());
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    private JPanel createButtons() {
        JPanel panel = new JPanel();
        ButtonGroup bg = new ButtonGroup();
        aRadioButton = new JRadioButton("A");
        bRadioButton = new JRadioButton("B");
        bRadioButton.addItemListener(this::handleItem);
        bg.add(aRadioButton);
        bg.add(bRadioButton);
        panel.add(aRadioButton);
        panel.add(bRadioButton);
        return panel;
    }

    private void handleItem(ItemEvent event) {
        if (event.getStateChange() == ItemEvent.SELECTED) {
            int result = JOptionPane.showConfirmDialog(frame,
                                                       "Are you sure?",
                                                       "Confirm",
                                                       JOptionPane.YES_NO_OPTION);
            switch (result) {
                case 0:
                    // YES
                    break;
                case -1:
                    // <ESC> or 'X'
                case 1:
                    // NO
                default:
                    aRadioButton.setSelected(true);
            }
            System.out.println("result = "   result);
        }
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(() -> new Intercep().buildAndDisplayGui());
    }
}

Note this line in the above code:

bRadioButton.addItemListener(this::handleItem);

This is referred to as a method reference.