java - 尝试获取 Radio Button.is Selected() 以设置标签的文本。不工作

Question

这是我的代码:

    panel2.add(question1);
    panel2.add(true1);
    panel2.add(false1);
    panel2.add(labelAnswer1);
    panel2.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));

    if(true1.isSelected()) {
        labelAnswer1.setText("You are CORRECT!");
    }

    else if(false1.isSelected()) {
        labelAnswer1.setText("You are wrong. The correct answer is " + true1.getText());
    }

    else if(true1.isSelected() && false1.isSelected()) {
        labelAnswer1.setText("You cannot select two answers!");
    }

不太确定我做错了什么。可能是晚上太晚了，哈哈。任何帮助，将不胜感激。谢谢并致以最诚挚的问候!

Answer 1

与大多数 GUI 框架一样，Swing 是事件驱动的，即发生某些事情然后您对其做出响应。您不知道这些事件可能发生的时间或顺序。

相反，您使用“监听器”(也称为 Observer Pattern)来注册您的组件，它会告诉您何时发生某些事情，并且您可以根据程序的当前状态采取适当的措施

看看How to Use Buttons, Check Boxes, and Radio Buttons和 How to Write an Action Listeners了解更多详情

import java.awt.EventQueue;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.ButtonGroup;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JRadioButton;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

    public Test() {
        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;
            gbc.anchor = GridBagConstraints.WEST;

            add(new JLabel("Is a banna:"), gbc);

            ButtonGroup bg = new ButtonGroup();
            ActionListener listener = new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    String cmd = e.getActionCommand();
                    System.out.println("You guessed " + cmd);
                    if ("Yellow".equalsIgnoreCase(cmd)) {
                        JOptionPane.showMessageDialog(TestPane.this, cmd + " is the answer");
                    } else {
                        JOptionPane.showMessageDialog(TestPane.this, cmd + " is not the answer");
                    }
                }
            };
            add(createGuess("Red", listener, bg), gbc);
            add(createGuess("Green", listener, bg), gbc);
            add(createGuess("Blue", listener, bg), gbc);
            add(createGuess("Yellow", listener, bg), gbc);
        }

        protected JRadioButton createGuess(String guess, ActionListener listener, ButtonGroup bg) {
            JRadioButton btn = new JRadioButton(guess);
            btn.addActionListener(listener);
            bg.add(btn);
            return btn;
        }

    }

}