如何修改JTextArea中Tab键的行为？
我正在Java
Swing中创建一个表单，其中一个字段是JTextArea。当我Tab在所有其他字段上使用键时，它将焦点移至下一个小部件，但在中JTextArea，它将在文本中插入制表符（水平空格）。
如何修改此行为？
回答：
/* This is my understanding of how tabbing works. The focus manager
recognizes the following default KeyStrokes for tabbing:
forwards: TAB or Ctrl-TAB
backwards: Shift-TAB or Ctrl-Shift-TAB
In the case of JTextArea, TAB and Shift-TAB have been removed from
the defaults which means the KeyStroke is passed to the text area.
The TAB KeyStroke inserts a tab into the Document. Shift-TAB seems
to be ignored.
This example shows different approaches for tabbing out of a JTextArea
Also, a text area is typically added to a scroll pane. So when
tabbing forward the vertical scroll bar would get focus by default.
Each approach shows how to prevent the scrollbar from getting focus.
*/
import java.awt.*;
import java.util.*;
import java.awt.event.*;
import javax.swing.*;
public class TextAreaTab extends JFrame
{
public TextAreaTab()
{
Container contentPane = getContentPane();
contentPane.setLayout(new BoxLayout(contentPane, BoxLayout.Y_AXIS));
contentPane.add( nullTraversalKeys() );
contentPane.add( writeYourOwnAction() );
contentPane.add( useKeyListener() );
contentPane.add( addTraversalKeys() );
}
// Reset the text area to use the default tab keys.
// This is probably the best solution.
private JComponent nullTraversalKeys()
{
JTextArea textArea = new JTextArea(3, 30);
textArea.setText("Null Traversal Keys\n2\n3\n4\n5\n6\n7\n8\n9");
JScrollPane scrollPane = new JScrollPane( textArea );
// scrollPane.getVerticalScrollBar().setFocusable(false);
textArea.setFocusTraversalKeys(KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, null);
textArea.setFocusTraversalKeys(KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, null);
return scrollPane;
}
// Replace the Tab Actions. A little more complicated but this is the
// only solution that will place focus on the component, not the
// vertical scroll bar, when tabbing backwards (unless of course you
// have manually prevented the scroll bar from getting focus).
private JComponent writeYourOwnAction()
{
JTextArea textArea = new JTextArea(3, 30);
textArea.setText("Write Your Own Tab Actions\n2\n3\n4\n5\n6\n7\n8\n9");
JScrollPane scrollPane = new JScrollPane( textArea );
InputMap im = textArea.getInputMap();
KeyStroke tab = KeyStroke.getKeyStroke("TAB");
textArea.getActionMap().put(im.get(tab), new TabAction(true));
KeyStroke shiftTab = KeyStroke.getKeyStroke("shift TAB");
im.put(shiftTab, shiftTab);
textArea.getActionMap().put(im.get(shiftTab), new TabAction(false));
return scrollPane;
}
// Use a KeyListener
private JComponent useKeyListener()
{
JTextArea textArea = new JTextArea(3, 30);
textArea.setText("Use Key Listener\n2\n3\n4\n5\n6\n7\n8\n9");
JScrollPane scrollPane = new JScrollPane( textArea );
scrollPane.getVerticalScrollBar().setFocusable(false);
textArea.addKeyListener(new KeyAdapter()
{
public void keyPressed(KeyEvent e)
{
if (e.getKeyCode() == KeyEvent.VK_TAB)
{
e.consume();
KeyboardFocusManager.
getCurrentKeyboardFocusManager().focusNextComponent();
}
if (e.getKeyCode() == KeyEvent.VK_TAB
&& e.isShiftDown())
{
e.consume();
KeyboardFocusManager.
getCurrentKeyboardFocusManager().focusPreviousComponent();
}
}
});
return scrollPane;
}
// Add Tab and Shift-Tab KeyStrokes back as focus traversal keys.
// Seems more complicated then just using null, but at least
// it shows how to add a KeyStroke as a focus traversal key.
private JComponent addTraversalKeys()
{
JTextArea textArea = new JTextArea(3, 30);
textArea.setText("Add Traversal Keys\n2\n3\n4\n5\n6\n7\n8\n9");
JScrollPane scrollPane = new JScrollPane( textArea );
scrollPane.getVerticalScrollBar().setFocusable(false);
Set set = new HashSet( textArea.getFocusTraversalKeys(
KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS ) );
set.add( KeyStroke.getKeyStroke( "TAB" ) );
textArea.setFocusTraversalKeys(
KeyboardFocusManager.FORWARD_TRAVERSAL_KEYS, set );
set = new HashSet( textArea.getFocusTraversalKeys(
KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS ) );
set.add( KeyStroke.getKeyStroke( "shift TAB" ) );
textArea.setFocusTraversalKeys(
KeyboardFocusManager.BACKWARD_TRAVERSAL_KEYS, set );
return scrollPane;
}
class TabAction extends AbstractAction
{
private boolean forward;
public TabAction(boolean forward)
{
this.forward = forward;
}
public void actionPerformed(ActionEvent e)
{
if (forward)
tabForward();
else
tabBackward();
}
private void tabForward()
{
final KeyboardFocusManager manager =
KeyboardFocusManager.getCurrentKeyboardFocusManager();
manager.focusNextComponent();
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
if (manager.getFocusOwner() instanceof JScrollBar)
manager.focusNextComponent();
}
});
}
private void tabBackward()
{
final KeyboardFocusManager manager =
KeyboardFocusManager.getCurrentKeyboardFocusManager();
manager.focusPreviousComponent();
SwingUtilities.invokeLater(new Runnable()
{
public void run()
{
if (manager.getFocusOwner() instanceof JScrollBar)
manager.focusPreviousComponent();
}
});
}
}
public static void main(String[] args)
{
TextAreaTab frame = new TextAreaTab();
frame.setDefaultCloseOperation( EXIT_ON_CLOSE );
frame.pack();
frame.setLocationRelativeTo(null);
frame.setVisible(true);
}
}
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