java - 如何检查 Swing 中的文本是否被选中？

Question

我有简单的 JTextField 和 KeyListener。

JTextField textField = new JTextField();
textField.addKeyListener(new KeyListener() {

@Override
   public void keyTyped(KeyEvent e)
   {
   }

   @Override
   public void keyPressed(KeyEvent e)
   {
   }

   @Override
   public void keyReleased(KeyEvent e)
   {
      validateThatTextWasSelectedWithShiftAndArrow();
   }
});

如何检查某人是否使用组合键(SHIFT + 向左或向右箭头)选择了文本？

Answer 1

Swing 大量使用 Key Bindings API以便轻松使用现有功能。我们已经知道JTextField完全有能力执行选择，我们只需要能够插入它即可。

JTextField使用 selection-backward和selection-forward要在激活系统相关击键时执行所需的功能，我们只需将代码注入(inject)其中即可。

为此，我写了一个简单的ReplaceAction行动，需要旧的 Action我们感兴趣，并调用两个方法，一个在旧的 Action 之前，一个在旧的之后叫做。这允许您将所需的功能注入(inject)到实现您尝试实现的任何功能所需的任何点...

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.Action;
import javax.swing.ActionMap;
import javax.swing.InputMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class MonitorSelection {

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

    public MonitorSelection() {
        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 {

        public TestPane() {
            setLayout(new GridBagLayout());
            JTextField field = new JTextField(10);
            add(field);
            InputMap im = field.getInputMap(WHEN_FOCUSED);
            ActionMap am = field.getActionMap();

            Action oldAction = am.get("selection-backward");
            am.put("selection-backward", new ReplacedAction(oldAction){
                @Override
                protected void doAfterReplacedAction() {
                    System.out.println("Before selection-backward");
                }

                @Override
                protected void doBeforeReplacedAction() {
                    System.out.println("After selection-backward");
                }

            });
            oldAction = am.get("selection-forward");
            am.put("selection-forward", new ReplacedAction(oldAction){
                @Override
                protected void doAfterReplacedAction() {
                    System.out.println("Before selection-forward");
                }

                @Override
                protected void doBeforeReplacedAction() {
                    System.out.println("After selection-forward");
                }

            });
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

    }

    public class ReplacedAction extends AbstractAction {
        private Action replaced;

        public ReplacedAction(Action replaced) {
            this.replaced = replaced;
        }

        @Override
        public void actionPerformed(ActionEvent e) {
            doBeforeReplacedAction();
            replaced.actionPerformed(e);
            doAfterReplacedAction();
        }

        protected void doBeforeReplacedAction() {
        }

        protected void doAfterReplacedAction() {
        }

    }

}