向 JtextArea 添加关键侦听器

Question

我有一个名为 input 的 JTextArea，当我按下向上箭头键时，我试图将字符串 inputValue 加载到其中。到目前为止，这段代码似乎不起作用，我不确定为什么。请帮忙。

    input.addKeyListener(new KeyListener() {            
        public void keyTyped(KeyEvent e) {
            System.out.println("test");
            if(e.getKeyCode() == KeyEvent.VK_UP) {
                input.setText(inputValue);
                System.out.println("up is pressed");
            }       
        }

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

        @Override
        public void keyReleased(KeyEvent e) {
            // TODO Auto-generated method stub      
        }
    });

Answer 1

在 JTextAreas 之类的 Swing 文本组件上使用 KeyListeners 之类的低级侦听器时应该小心，因为弄乱这些侦听器会导致文本组件行为异常。

如果您要查找对文档的更改，最好使用 DocumentListener；如果您想在发生之前侦听并阻止或更改文本条目，则使用 DocumentFilter。

如果您只想收到向上箭头等键的通知，我会使用键绑定——JTextArea 使用自己来通知按键并对按键做出反应，并将键绑定替换为新的一。如果您小心地执行此操作，您甚至可以在新操作中调用与按键相关的原始操作。例如：

import java.awt.event.ActionEvent;
import java.awt.event.KeyEvent;
import javax.swing.*;

@SuppressWarnings("serial")
public class TextAreaTrapUp extends JPanel {
    private JTextArea textArea = new JTextArea(20, 40);

    public TextAreaTrapUp() {
        // get JTextArea's InputMap and ActionMap
        int condition = JComponent.WHEN_FOCUSED;
        InputMap inputMap = textArea.getInputMap(condition);
        ActionMap actionMap = textArea.getActionMap();

        // get the up keystroke
        KeyStroke upKeyStroke = KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0);
        String upKey = (String) inputMap.get(upKeyStroke); // get the input map's key for this keystorke
        Action originalUpAction = actionMap.get(upKey); // and get the action map's original action for this key

        Action newUpAction = new NewUpAction(originalUpAction); // create our new up action passing in the old one
        actionMap.put(upKey, newUpAction); // and set this into our ActionMap

        textArea.setWrapStyleWord(true);
        textArea.setLineWrap(true);
        add(new JScrollPane(textArea));
    }

    // Action called when up-arrow pressed
    private class NewUpAction extends AbstractAction {
        private Action originalUpAction; // the original action

        public NewUpAction(Action originalUpAction) {
            this.originalUpAction = originalUpAction;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            System.out.println("Up Arrow Pressed");

            // if you want to move the caret up, then call the original action
            // as well
            if (originalUpAction != null) {
                originalUpAction.actionPerformed(e);
            }
        }
    }

    private static void createAndShowGui() {
        TextAreaTrapUp mainPanel = new TextAreaTrapUp();

        JFrame frame = new JFrame("TextAreaTrapUp");
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationByPlatform(true);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}

Answer 2

你应该覆盖 void keypressed 而不是 keytyped

@Override
        public void keyPressed(KeyEvent e) {
            System.out.println("test");
            if(e.getKeyCode() == KeyEvent.VK_UP) {
                input.setText(inputValue);
                System.out.println("up is pressed");

        }

因为它不是角色