向JtextArea添加键监听器

Question

我有一个名为input的JTextArea，我试图在按下向上箭头键时将字符串inputValue加载到它中。到目前为止，这段代码似乎不起作用，我不确定原因。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

你应该覆盖无效的keyPressed代替的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"); 

     } 

，因为它不是一个卡拉科特

Answer 2

使用低级别的听众像Swing文本组件，如JTextAreas KeyListeners时，你要小心，因为搞乱这些可能会导致文本组件行为不当。

更好的方法是使用DocumentListener，如果您正在寻找文档或DocumentFilter的更改，如果您想要侦听并阻止或更改之前的文本条目它发生。

如果你只是想要得到诸如向上箭头之类的关键字的通知，我会使用键绑定--JTextArea使用它自己来通知键响应并对其作出反应，并将键替换新的一个。如果您谨慎操作，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()); 
    } 
}