java - 监听 ButtonGroup 的“子”变化，并打印选定的 JRadioButton 的文本

Question

我想要的是：如果选择了 ButtonGroup 中包含的 JRadioButton，则创建一个触发的事件，然后打印 JRadioButton 上的文本。

Answer 1

根据我的评论，您不能将侦听器添加到 ButtonGroup。您可能必须使用添加到单个 JRadioButtons 的 ActionListener。

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编辑 1
我想你总是可以扩展ButtonGroup 以便它接受 ActionListeners。例如：

import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.AbstractButton;
import javax.swing.ButtonGroup;
import javax.swing.ButtonModel;
import javax.swing.event.EventListenerList;

@SuppressWarnings("serial")
public class MyButtonGroup extends ButtonGroup {
   private ActionListener btnGrpListener = new BtnGrpListener();
   private EventListenerList listenerList = new EventListenerList();

   @Override
   public void add(AbstractButton b) {
      b.addActionListener(btnGrpListener);
      super.add(b);
   }

   public void addActionListener(ActionListener listener) {
      listenerList.add(ActionListener.class, listener);
   }

   public void removeActionListener(ActionListener listener) {
      listenerList.remove(ActionListener.class, listener);
   }

   protected void fireActionListeners() {
      Object[] listeners = listenerList.getListenerList();
      String actionCommand = "";
      ButtonModel model = getSelection();
      if (model != null) {
         actionCommand = model.getActionCommand();
      }
      ActionEvent ae = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, actionCommand);
      for (int i = listeners.length-2; i>=0; i-=2) {
          if (listeners[i]== ActionListener.class) {
              ((ActionListener)listeners[i+1]).actionPerformed(ae);
          }
      }
   }

   private class BtnGrpListener implements ActionListener {

      public void actionPerformed(ActionEvent ae) {
         fireActionListeners();
      }
   }
}

并通过以下测试：

import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.*;

public class MyButtonGroupTest {
   private static void createAndShowUI() {
      String[] data = {"Monday", "Tuesday", "Wednesday", "Thursday", "Friday"};

      JPanel panel = new JPanel(new GridLayout(0, 1));
      MyButtonGroup myBtnGrp = new MyButtonGroup();
      myBtnGrp.addActionListener(new ActionListener() {
         public void actionPerformed(ActionEvent e) {
            System.out.println("Action Command is: " + e.getActionCommand());
         }
      });

      for (String text : data) {
         JRadioButton radioBtn = new JRadioButton(text);
         radioBtn.setActionCommand(text);
         myBtnGrp.add(radioBtn);
         panel.add(radioBtn);
      }

      JFrame frame = new JFrame("MyButtonGroupTest");
      frame.getContentPane().add(panel);
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

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

但这最终仍然会为每个 JRadioButton 添加 ActionListers 以达到其目的；它只是在 MyButtonGroup 的 add 方法覆盖的幕后执行此操作。