Java JTextArea中选择文本触发哪个事件? [英] Which event a selection of text trigger in Java JTextArea?

问题描述

我想监视JTextArea中文本的选择.我不知道选择文本触发会发生什么情况.

I want to monitor the selection of text into the a JTextArea. I don't know what event a selection of text triggers.

我只想在从JTextArea中选择了某些文本(例如在菜单中复制和剪切选项)后立即启用某些菜单项.我应该为此监视什么?

I just want to enable some of the menu items as soon as some text is selected out of the JTextArea like copy and cut options into the menu. What should I monitor for that?

推荐答案

我不知道文本组件的任何选择侦听器"(尽管它们可能有用)，但是您可以使用CaretListener来监视更改到插入符号位置并检查选择状态...

I don't know about any "selection listeners" for text components (although they might be useful), but you could use a CaretListener to monitor changes to the caret position and check the selection state...

public class TestSelectionMonitor {

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

    public TestSelectionMonitor() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                }

                final JTextArea ta = new JTextArea();
                ta.addCaretListener(new CaretListener() {
                    @Override
                    public void caretUpdate(CaretEvent e) {
                        int length = ta.getSelectionEnd() - ta.getSelectionStart();
                        System.out.println(length);
                    }
                });

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new JScrollPane(ta));
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

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