如何确定哪些行在可滚动的JTextArea中可见? [英] How to determine which lines are visible in scrollable JTextArea?

问题描述

如何确定可滚动JTextArea(JScrollPane内部的JTextArea)中的第一条可见行的数量和当前可见的行数?

How to determine number of the first visible line and the number of lines currently visible in scrollable JTextArea (JTextArea inside a JScrollPane)?

推荐答案

好的，这是我对这个问题的看法...(虽然是个好问题)

Okay, this is my take on the problem... (Nice question though)

此解决方案需要您考虑一些问题.它将返回部分显示的行.

There is a small consideration you need to have with this solution. It will return partially displayed lines.

public class TestTextArea {

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

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

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(new TestTextAreaPane());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class TestTextAreaPane extends JPanel {

        private JTextArea textArea;
        private JTextArea viewText;

        public TestTextAreaPane() {
            setLayout(new GridLayout(2, 1));
            textArea = new JTextArea(20, 100);
            textArea.setWrapStyleWord(true);
            textArea.setLineWrap(true);
            textArea.setText(loadText());

            viewText = new JTextArea(20, 100);
            viewText.setWrapStyleWord(false);
            viewText.setLineWrap(false);
            viewText.setEditable(false);

            JScrollPane scrollPane = new JScrollPane(textArea);
            add(scrollPane);

            add(viewText);

            scrollPane.getViewport().addChangeListener(new ChangeListener() {
                @Override
                public void stateChanged(ChangeEvent e) {
                    if (textArea.getText().length() > 0) {
                        JViewport viewport = (JViewport) e.getSource();
                        Rectangle viewRect = viewport.getViewRect();

                        Point p = viewRect.getLocation();
                        int startIndex = textArea.viewToModel(p);

                        p.x += viewRect.width;
                        p.y += viewRect.height;
                        int endIndex = textArea.viewToModel(p);

                        if (endIndex - startIndex >= 0) {

                            try {
                                viewText.setText(textArea.getText(startIndex, (endIndex - startIndex)));
                            } catch (BadLocationException ex) {
                                ex.printStackTrace();
                                viewText.setText(ex.getMessage());
                            }

                        }

                    }

                }
            });

        }

        protected String loadText() {
            String text = null;
            File file = new File("src/testtextarea/TestTextArea.java");

            BufferedReader br = null;
            try {
                br = new BufferedReader(new FileReader(file));
                StringBuilder sb = new StringBuilder(128);
                String read = null;
                while ((read = br.readLine()) != null) {
                    sb.append(read).append("\n");
                }

                text = sb.toString();
            } catch (IOException exp) {
                exp.printStackTrace();
            } finally {
                try {
                    br.close();
                } catch (Exception e) {
                }
            }

            return text;
        }
    }
}

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