Question

我有一个名为input的JTextArea，当我按向上箭头键时，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Swing文本组件（如JTextAreas）上使用像KeyListeners这样的低级侦听器时应该注意，因为搞乱这些可能会导致文本组件出错。

如果您想要在之前监听和阻止或更改文本条目，那么如果您正在寻找对文档或DocumentFilter的更改，那么使用DocumentListener会更好。

如果您只是希望收到诸如向上箭头之类的密钥的通知，我将使用密钥绑定 - JTextArea使用什么来通知和响应按键，并将替换密钥绑定新的那一个。如果您小心翼翼地执行此操作，您甚至可以在新操作中调用与按键相关联的原始操作。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");

        }

因为它不是一个特色

将关键侦听器添加到JtextArea

2 个答案: