java - 为什么我的 JPanel 在 JScrollPane 中不滚动？

Question

我在 JScrollPane 中放置了一个 JPanel(黄色)。

当我在 JTextPane 中输入一些文本时，它会调整大小，但垂直滚动条仍未激活。 yelowPanel.getSize() 返回与之前相同的值。`(您可以在 redPanel 上看到它)。

那么如何刷新yellowPanel呢？我想垂直滚动面板。 我试图:

panelCreating.revalidate();
panelCreating.invalidate();
panelCreating.repaint();

仅适用于 panelCreating.setPreferredSize(new Dimension(333, 777)); 但我不知道要设置什么大小。这取决于内容。

有一个小例子:

package swingtest;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.GridBagConstraints;
import java.awt.GridBagLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.swing.BorderFactory;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;

public class SwingTest extends JFrame {

    public SwingTest() {
        initComponents();
    }

    public static void main(String[] args) {
        java.awt.EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                new SwingTest().setVisible(true);
            }
        });
    }
    private JPanel panelCenter, panelCreating;
    private JScrollPane scrollPaneCreating, scrollPaneCenter;
    private JTextPane textPane1, textPane2;
    private JButton button1;

    private void initComponents() {
        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setMinimumSize(new Dimension(300, 300));

        panelCreating = new JPanel();
        panelCreating.setMinimumSize(new Dimension(160, 200));
        panelCreating.setPreferredSize(new Dimension(160, 200));
        scrollPaneCreating = new JScrollPane(panelCreating,
            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
            JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

        textPane1 = new JTextPane();
        textPane1.setText("a\na");
        textPane2 = new JTextPane();
        textPane2.setText("b\nb");
        button1 = new JButton("+++");

        panelCenter = new JPanel();
        panelCenter.setBackground(Color.blue);
        scrollPaneCenter = new JScrollPane(panelCenter);



        // ----------------- Left Panel Init -----------------------

        panelCreating.setLayout(new GridBagLayout());
        panelCreating.setBackground(Color.ORANGE);
        panelCreating.setBorder(BorderFactory.createEmptyBorder(8, 8, 8, 8));

        GridBagConstraints c = new GridBagConstraints();
        c.insets = new Insets(0, 0, 4, 4);
        c.anchor = GridBagConstraints.FIRST_LINE_START;
        c.weightx = c.weighty = 0;

        c.gridx = 0;
        c.gridy = GridBagConstraints.RELATIVE;
        c.gridwidth = GridBagConstraints.REMAINDER;
        c.gridheight = 1;
        c.fill = GridBagConstraints.BOTH;
        panelCreating.add(textPane1, c);

        button1.addActionListener(new ActionListener() {

            int height = 50;

            @Override
            public void actionPerformed(ActionEvent e) {
                textPane1.setText(textPane1.getText() + "\na");
                textPane1.setPreferredSize(new Dimension(150, height));
                textPane2.setText(textPane2.getText() + "\nb");
                textPane2.setPreferredSize(new Dimension(150, height));
                height += 30;

                panelCreating.revalidate();
                panelCreating.repaint();
                scrollPaneCreating.revalidate();
            }
        });
        panelCreating.add(button1, c);

        panelCreating.add(textPane2, c);

        // -------------------------------------------------------

        getContentPane().setLayout(new GridBagLayout());
        c = new GridBagConstraints();

        c.ipadx = c.ipady = 0;
        c.insets = new Insets(0, 0, 0, 0);
        c.weighty = 0;
        c.gridheight = 1;
        c.gridx = 0;
        c.gridy = 1;
        c.gridwidth = 1;
        c.weightx = 0;
        c.fill = GridBagConstraints.BOTH;
        getContentPane().add(scrollPaneCreating, c);


        c.gridx = 1;
        c.gridy = 1;
        c.fill = GridBagConstraints.BOTH;
        c.weightx = 1;
        c.weighty = 1;
        getContentPane().add(scrollPaneCenter, c);

    }
}

黄色面板也使用了GridBagLayout。 对不起我的英语

Answer 1

不是在 panelCreating 上设置首选大小，而是在 scrollPaneCreating 上设置它。并且不要在文本组件上设置首选大小，它们会随着您向其中添加新文本行而增长。这个想法是让滚动 Pane 内的面板根据需要变大，并且只限制滚动 Pane 本身的大小。

    // [...]

    panelCreating = new JPanel();
    //panelCreating.setMinimumSize(new Dimension(160, 200));
    //panelCreating.setPreferredSize(new Dimension(160, 200));
    scrollPaneCreating = new JScrollPane(panelCreating,
        JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
        JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
    scrollPaneCreating.setMinimumSize(new Dimension(160, 200));
    scrollPaneCreating.setPreferredSize(new Dimension(160, 200));

    // [...]

        @Override
        public void actionPerformed(ActionEvent e) {
            textPane1.setText(textPane1.getText() + "\na");
            //textPane1.setPreferredSize(new Dimension(150, height));
            textPane2.setText(textPane2.getText() + "\nb");
            //textPane2.setPreferredSize(new Dimension(150, height));
            //height += 30;

            // This isn't necessary either
            //panelCreating.revalidate();
            //panelCreating.repaint();
            //scrollPaneCreating.revalidate();
        }

---

编辑添加:另一种方法是在附加到滚动 Pane 的 JViewport 上设置大小。视口(viewport)是显示内容的地方。您可以将滚动 Pane 视为由视口(viewport)和滚动条组成。如果滚动 Pane 设置为固定大小，则视口(viewport)大小通过减去滚动条大小来确定。但如果视口(viewport)设置为固定大小，则滚动 Pane 大小由滚动条大小与视口(viewport)大小相加决定。如果您想精确控制应在屏幕上显示多少内容，则最好在视口(viewport)上设置固定大小，因为滚动条大小会因操作系统而异。

scrollPaneCreating.getViewport().setMinimumSize(new Dimension(160, 200));
scrollPaneCreating.getViewport().setPreferredSize(new Dimension(160, 200));