Java JTextPane 向 JScrollPane 添加空白区域

Question

我在 JScrollPane 中有一个 JTextPane。我想要实现的是在 JTextPane 下添加一个空白空间，以允许用户进一步向下滚动文本 Pane ，以便最后一行(在框架底部可见) 可以向上滚动到第一行位置。很难解释所以这里有一些照片:

我尝试解决这个问题是在 JTextPane 下添加一个带有 Borderlayout.SOUTH 的 JPanel。并更新 setPreferredSize(0, frameHeight - (const+ fontHeight))

const = A constant value I got from experimenting

int fontHeight = textPane.getFontMetrics(textPane.getFont()).getHeight();

在您调整字体大小之前，它工作正常...基本上它非常 hacky 并且似乎不是很可靠。

问题:是否有内部方法可以添加此功能？如果没有，我该如何改进现有解决方案以提高稳定性？

编辑----------------这里是工作代码:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Insets;
import java.awt.Rectangle;
import java.awt.event.ComponentAdapter;
import java.awt.event.ComponentEvent;

import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.JViewport;
import javax.swing.SwingUtilities;
import javax.swing.border.EmptyBorder;
import javax.swing.text.BadLocationException;


public class Main extends JFrame{
    private JTextPane zNum, tField;
    private JPanel scrollPanel;
    private JScrollPane tScrollPane;
    private Font font = new Font("Source Code Pro", Font.PLAIN, 12);

public Main(){
    super("Test Editor");
    getContentPane().setLayout(new BorderLayout());

    zNum = new JTextPane();
    zNum.setText("1");
    zNum.setEditable(false);
    zNum.setBorder(new EmptyBorder(2, 6, 2, 6));
    zNum.setBackground(Color.GRAY);
    zNum.setFont(font);

    tField = new JTextPane();
    tField.setBorder(new EmptyBorder(2, 6, 2, 6));
    tField.setBackground(Color.LIGHT_GRAY);
    tField.setFont(font);

    scrollPanel = new JPanel();
    scrollPanel.setLayout(new BorderLayout());
    scrollPanel.add(zNum, BorderLayout.LINE_START);
    scrollPanel.add(tField, BorderLayout.CENTER);
    scrollPanel.setBackground(Color.LIGHT_GRAY);

    tScrollPane = new JScrollPane(scrollPanel);
    tScrollPane.setBorder(BorderFactory.createEmptyBorder());
    getContentPane().add(tScrollPane, BorderLayout.CENTER);

    setPreferredSize(new Dimension(300, 200));
    setDefaultCloseOperation(DISPOSE_ON_CLOSE);
    setResizable(true);
    pack();
    setLocationRelativeTo(null);
    setVisible(true);

    // Resize
    this.addComponentListener(new ComponentAdapter() {
        public void componentResized(ComponentEvent event) {
            updateMargin(tField);
        }
    });
}

void updateMargin(JTextPane textPane) {
    JViewport viewport = (JViewport)
        SwingUtilities.getAncestorOfClass(JViewport.class, textPane);

    if (viewport != null) {
        int len = textPane.getDocument().getLength();
        try {
            Rectangle end = textPane.modelToView(len);
            if (end != null) {
                tField.setBorder(new EmptyBorder(0, 0, viewport.getHeight() - (end.height + 4), 0));
            }
        } catch (BadLocationException e) {
            throw new RuntimeException(e);
        }
    }
}

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

Answer 1

您可以根据其封闭的 JViewport 的边界及其文档的最后一行来设置 JTextPane 的边距:

static void updateMargin(JTextPane textPane) {
    JViewport viewport = (JViewport)
        SwingUtilities.getAncestorOfClass(JViewport.class, textPane);

    if (viewport != null) {
        Insets margin = textPane.getMargin();

        int len = textPane.getDocument().getLength();
        try {
            Rectangle end = textPane.modelToView(len);
            if (end != null) {
                margin.bottom = viewport.getHeight() - end.height;
                textPane.setMargin(margin);
            }
        } catch (BadLocationException e) {
            throw new RuntimeException(e);
        }
    }
}

每当调整 JTextPane 的大小时、当它变得可显示时以及当它的文本发生更改时，您都希望调用该方法。为了更好地衡量，如果调用 JTextPane 的继承 setPage 方法，我也会调用它:

static void configureMargin(final JTextPane textPane) {
    textPane.addPropertyChangeListener("page", new PropertyChangeListener() {
        @Override
        public void propertyChange(PropertyChangeEvent event) {
            updateMargin(textPane);
        }
    });

    textPane.addHierarchyListener(new HierarchyListener() {
        @Override
        public void hierarchyChanged(HierarchyEvent event) {
            long flags = event.getChangeFlags();
            if ((flags & HierarchyEvent.DISPLAYABILITY_CHANGED) != 0) {
                updateMargin(textPane);
            }
        }
    });

    textPane.addComponentListener(new ComponentAdapter() {
        @Override
        public void componentResized(ComponentEvent event) {
            updateMargin(textPane);
        }
    });

    textPane.getDocument().addDocumentListener(new DocumentListener() {
        private void updateTextPane() {
            EventQueue.invokeLater(new Runnable() {
                public void run() {
                    updateMargin(textPane);
                }
            });
        }

        @Override
        public void changedUpdate(DocumentEvent event) {
            updateTextPane();
        }

        @Override
        public void insertUpdate(DocumentEvent event) {
            updateTextPane();
        }

        @Override
        public void removeUpdate(DocumentEvent event) {
            updateTextPane();
        }
    });
}