Java ActionListener 将变量返回到包含 ActionListener 的方法

Question

我有一个这样的方法，给定一个JButton 数组，并在按下它们时返回它们的文本：

public static String foo(JButton[] buttons) {
    for (JButton i : buttons) {
        i.addActionListener(new ActionListener() {
            @Override
            public void actionPerformed(ActionEvent e) {
                return i.getText();
            }
        });
    }
}

但是，当然，这段代码不会编译，因为我将一个变量返回给一个 null 方法。那么，我如何让i.getText() 也通过foo() 方法返回其输出？

---

编辑，所有代码：

import java.awt.Color;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;

import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class JCustomFrame {
    public static void showMessageFrame(String title, String message,
            String[] textOnButtons, ImageIcon icon) {
        final JFrame frame = new JFrame();
        JPanel panel = new JPanel();

        panel.setLayout(new GridBagLayout());
        panel.setBackground(Color.WHITE);

        GridBagConstraints c = new GridBagConstraints();
        c.anchor = GridBagConstraints.EAST;
        c.fill = GridBagConstraints.RELATIVE;
        c.gridx = 0;
        c.gridy = 0;
        c.insets = new Insets(5, 5, 5, 5);

        JLabel messageLabel = new JLabel(message);
        messageLabel.setFont(messageLabel.getFont().deriveFont(16.0f));

        panel.add(messageLabel, c);

        c.gridy = 1;
        c.gridx = 0;
        for (int i = 0; i < textOnButtons.length; i++) {
            JButton button = new JButton(textOnButtons[i]);
            button.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent arg0) {
                    return ((JButton) arg0.getSource()).getText();
                    frame.dispose();
                }
            });
            button.setFont(button.getFont().deriveFont(16.0f));
            panel.add(button, c);
            c.gridx++;
        }

        if (icon == null) {
            frame.setIconImage(new BufferedImage(1, 1,
                    BufferedImage.TYPE_INT_ARGB_PRE));
        } else {
            frame.setIconImage(icon.getImage());
        }
        frame.add(panel);
        frame.setTitle(title);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.pack();
    }

    public static void main(String[] args) {
        JCustomFrame.showMessageFrame("Test Frame",
                "Do you really want to do this?", new String[] { "Hell No",
                        "Sure, Why Not" }, null);
    }
}

Answer 1

这个说法没有意义：

那么，我如何让 i.getText() 也通过 foo() 方法返回其输出？

根据事件驱动编程的规则，在将 ActionListener 添加到按钮后，方法 foo() 将不再运行，并且肯定会在用户按下按钮时结束。相反，尽管您可以让 ActionListeners 更改类的状态，但任何类都应该足够了。例如：

class FooClass {
    private String text;

    public void foo(JButton[] buttons) {
        for (JButton i : buttons) {
            i.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    text = e.getActionCommand(); 
                }
            });
        }
    }
}

如果您需要有关可行解决方案的更多详细信息，请告诉我们有关您的实际程序和具体问题的更多详细信息。

现在，如果您确实需要一种方法来返回所按下按钮的值，则需要通过通知机制和回调方法来完成此操作，但同样，解决方案的细节将取决于实际的细节问题和代码。

---

编辑

您正在尝试模拟 JOptionPane。您的解决方案是使用 JOptionPane，向其中添加 JPanel，或者使用模态 JDialog 创建自己的：

import java.awt.Color;
import java.awt.Component;
import java.awt.Dialog.ModalityType;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.Window;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.image.BufferedImage;
import javax.swing.ImageIcon;
import javax.swing.JButton;
import javax.swing.JDialog;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class JCustomFrame2 {

   public static String showMessageFrame(Window owner, String title,
         String message, String[] textOnButtons, ImageIcon icon) {
      final JDialog dialog = new JDialog(owner);
      StringBuilder sb = new StringBuilder();

      // make it application modal!
      dialog.setModalityType(ModalityType.APPLICATION_MODAL);
      JPanel panel = new JPanel();

      panel.setLayout(new GridBagLayout());
      panel.setBackground(Color.WHITE);

      GridBagConstraints c = new GridBagConstraints();
      c.anchor = GridBagConstraints.EAST;
      c.fill = GridBagConstraints.RELATIVE;
      c.gridx = 0;
      c.gridy = 0;
      c.insets = new Insets(5, 5, 5, 5);

      JLabel messageLabel = new JLabel(message);
      messageLabel.setFont(messageLabel.getFont().deriveFont(16.0f));

      panel.add(messageLabel, c);

      c.gridy = 1;
      c.gridx = 0;
      for (int i = 0; i < textOnButtons.length; i++) {
         JButton button = new JButton(textOnButtons[i]);
         button.addActionListener(new ButtonListener(sb));
         button.setFont(button.getFont().deriveFont(16.0f));
         panel.add(button, c);
         c.gridx++;
      }

      if (icon == null) {
         dialog.setIconImage(new BufferedImage(1, 1,
               BufferedImage.TYPE_INT_ARGB_PRE));
      } else {
         dialog.setIconImage(icon.getImage());
      }
      dialog.add(panel);
      dialog.setTitle(title);
      dialog.setDefaultCloseOperation(JDialog.DISPOSE_ON_CLOSE);
      dialog.pack();
      dialog.setVisible(true);

      return sb.toString();
   }

   private static class ButtonListener implements ActionListener {
      private StringBuilder sb;

      public ButtonListener(StringBuilder sb) {
         this.sb = sb;
      }


      @Override
      public void actionPerformed(ActionEvent e) {
         sb.append(e.getActionCommand());
         Component component = (Component) e.getSource();
         Window win = SwingUtilities.getWindowAncestor(component);
         if (win != null) {
            win.dispose();
         }
      }
   }

   public static String showMessageFrame(String title,
         String message, String[] textOnButtons, ImageIcon icon) {
      return showMessageFrame(null, title, message, textOnButtons, icon);
   }


   public static void main(String[] args) {
      String result = JCustomFrame2.showMessageFrame("Test Frame",
            "Do you really want to do this?", new String[] { "Hell No",
                  "Sure, Why Not" }, null);

      System.out.println(result);
   }
}

Answer 2

为什么这么复杂？无论foo 应该做什么，只要简单地从ActionListener 内部调用另一个方法，并将按钮的名称作为参数，就会容易得多。或者，如果你真的想实现这样的目标，让线程等待用户按下按钮。

public void doSomething(){
    JButton[] someButtons = ...;//whereever you create the buttons

    System.out.println(foo(someButtons));
}

public static String foo(JButton[] buttons){
    final String someString = "";

    final Object lock = new Object();

    for(JButton b : buttons){
        b.addActionListener(e -> {
             someString.concat(b.getName());

             synchronized(lock){
                 lock.notifyAll();
             }
        });
    }

    synchronized(lock){
        try{
            lock.wait();
        }catch(InterruptedException e){}
    }

    return someString;
}