无法找出 ActionListener 的错误

Question

以下是我的程序。目标是在用户输入数字并按下回车键后，将罗马数字转换为阿拉伯数字。

这是一项家庭作业，我们被迫使用 JTextAreas 代替 JTextFields。

我的错误存在于行：enterRomanNumber.addActionListener(handler)；错误内容为：

"The method addActionListener(ArabicToRomanGUI.HandlerForTextArea) is undefined for the type JTextArea"

我似乎无法弄清楚为什么我会收到此错误或如何更正它，请有人指教。

import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.ActionEvent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JTextField;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JTextArea;
public class ArabicToRomanGUI extends JFrame
{
private static final long serialVersionUID = 1L;
private JTextArea enterRomanNumber = new JTextArea();
JLabel label = new JLabel();
JPanel panel = new JPanel();
JFrame frame = new JFrame();


//TestArea contructor adds jtextArea to jframe
public ArabicToRomanGUI()
{
    super("Convert a Roman Numeral");
    setLayout(new FlowLayout());

    //Text field to enter a roman numeral
    enterRomanNumber = new JTextArea(1,25);
    enterRomanNumber.setText("Delete this text and Enter a Roman Numerial Here!");
    //enterRomanNumber.setAlignmentX(0);
    //enterRomanNumber.setAlignmentY(0);

    add(enterRomanNumber);

    HandlerForTextArea handler = new HandlerForTextArea();
    enterRomanNumber.addActionListener(handler);
}

private class HandlerForTextArea implements ActionListener
{
    //used to process textArea events
    @Override
    public void actionPerformed(ActionEvent e) 
    {
        String userInput = "";
        userInput = enterRomanNumber.getText();
        userInput = userInput.toUpperCase();

        ConversionLogic.ConvertFromRomanToArabic(userInput); //converts user string of Roman numerals to an int in arabic
        String arabicNumberAsString = ConversionLogic.getConvertedRomanNumeral();
        enterRomanNumber.setText(arabicNumberAsString);

        //user pressed enter in JTextField enterNumberField
        if(e.getSource() == enterRomanNumber)
        {
            //enterRomanNumber.setText(arabicNumberAsString);
            if (ConversionLogic.getCheckFail() == true)
            {
                JOptionPane.showMessageDialog(frame, "The Roman Numeral entered is Invalid", "Error", JOptionPane.ERROR_MESSAGE);
            }
            else
            {
                JOptionPane.showMessageDialog(frame, "The arabic equivalent is " + arabicNumberAsString + "." , "Conversion Successful", JOptionPane.PLAIN_MESSAGE);
            }
        }

    }
}
}//end inner class TextAreaHandler

Answer 1

要获得更好的答案，请参阅@MadProgrammer 的答案。

我的解决方案：

JTextArea 没有 ActionListener。

所以只用KeyListener代替

HandlerForTextArea handler = new HandlerForTextArea();
enterRomanNumber.addKeyListener(handler);

实现 KeyListener

private class HandlerForTextArea implements KeyListener
{

    @Override
    public void keyPressed(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }

    @Override
    public void keyReleased(KeyEvent arg0) {
        // TODO Auto-generated method stub
        if (arg0.getKeyCode() == VK_ENTER){
            // TODO Your bussiness
        }
    }

    @Override
    public void keyTyped(KeyEvent arg0) {
        // TODO Auto-generated method stub
    }
}

Answer 2

KeyListeners 从来都不是与文本组件一起使用的合适解决方案，如果你想在文本组件更改时得到通知，你可以使用 DocumentListener，如果你想 change/filter 什么可以输入到文本组件中，你使用DocumentFilter，如果你需要更改一个特殊的键，比如Enter，你应该使用一个键绑定[=22] =]

有关详细信息，请参阅 How to Use Key Bindings。

使用 KeyListener 可能遇到的一个问题是不知道文本组件何时处理击键，在您的情况下，这可能不是主要问题，但它可能会改变方式该程序适用于不同的平台。

相反，您可以覆盖 JTextArea 对 Enter 键（名为 insert-break）的键绑定。这为您提供了实际更改击键行为的能力，或者，在您的情况下，管理您处理事件的方式。例如，这将替换文本区域的 Enter 键的 Action，但保留 previous/default 行为...

import java.awt.BorderLayout;
import java.awt.EventQueue;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextArea;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class KeyBindingsTest {

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

    public KeyBindingsTest() {
        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 {

        private JTextArea ta;

        public TestPane() {
            ta = new JTextArea(10, 20);
            ActionMap am = ta.getActionMap();

            Action proxy = am.get("insert-break");
            am.put("insert-break", new AbstractAction() {
                @Override
                public void actionPerformed(ActionEvent e) {
                    // You can process the event through the original action BEFORE
                    // you do your own processing
                    //proxy.actionPerformed(e);
                    System.out.println("You pressed the enter key, you can have candy");
                    // Or you can process the event through the original action AFTER
                    // you do your own processing, you have now gained control
                    proxy.actionPerformed(e);
                }
            });

            setLayout(new BorderLayout());
            add(ta);
        }

    }

}

现在，您甚至可以创建自己的 JTextArea 支持 ActionPerformed...

public class ActionableTextArea extends JTextArea {

    private String actionCommand;

    public ActionableTextArea() {
        installKeyBindings();
    }

    public ActionableTextArea(String text) {
        super(text);
        installKeyBindings();
    }

    public ActionableTextArea(int rows, int columns) {
        super(rows, columns);
        installKeyBindings();
    }

    public ActionableTextArea(String text, int rows, int columns) {
        super(text, rows, columns);
        installKeyBindings();
    }

    public ActionableTextArea(Document doc) {
        super(doc);
        installKeyBindings();
    }

    public ActionableTextArea(Document doc, String text, int rows, int columns) {
        super(doc, text, rows, columns);
        installKeyBindings();
    }

    protected void installKeyBindings() {
        ActionMap am = getActionMap();
        Action proxy = am.get("insert-break");
        am.put("insert-break", new AbstractAction() {
            @Override
            public void actionPerformed(ActionEvent e) {
                    // You can process the event through the original action BEFORE
                // you do your own processing
                //proxy.actionPerformed(e);
                fireActionPerformed();
                    // Or you can process the event through the original action AFTER
                // you do your own processing, you have now gained control
                proxy.actionPerformed(e);
            }
        });
    }

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

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

    public void setActionCommand(String actionCommand) {
        this.actionCommand = actionCommand;
    }

    public String getActionCommand() {
        return actionCommand;
    }

    protected void fireActionPerformed() {
        ActionListener[] listeners = listenerList.getListeners(ActionListener.class);
        if (listeners.length > 0) {
            ActionEvent evt = new ActionEvent(this, ActionEvent.ACTION_PERFORMED, getActionCommand());
            for (ActionListener listener : listeners) {
                listener.actionPerformed(evt);
            }
        }
    }

}

无法找出 ActionListener 的错误

Can't figure out error with ActionListener

java

swing

actionlistener

jtextarea