为什么JOptionPane中的JScrollPane没有显示其所有内容？

Question

我正在尝试将组件添加到JPanel，然后将此面板放入JScrollPane，然后将JScrollPane放入JOptionPane。

问题：只添加了19行组件。有一个for循环可以确定组件的行数，如果将条件计数器更改为19或更小，则会显示所有这些。

这是问题的SSCCE

import java.awt.Dimension;
import javax.swing.GroupLayout;
import javax.swing.JButton;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.SwingConstants;

public class DynamicGroupLayout extends JPanel
{

    JButton addRecordButton;
    JTextField[] FieldsArray;
    JLabel[] LabelsArray;
    GroupLayout layout;
    JScrollPane scrollPane;

    public DynamicGroupLayout()
    {
        addRecordButton = new JButton("add record");
        layout = new GroupLayout(this);
        this.setLayout(layout);
        layout.setAutoCreateGaps(true);
        layout.setAutoCreateContainerGaps(true);

        scrollPane = new JScrollPane(this);
        scrollPane.getVerticalScrollBar().setUnitIncrement(16);
        scrollPane.setPreferredSize(this.getPreferredSize());

        setTextFields();
        showDialog();
    }

    @Override
    public Dimension getPreferredSize()
    {
        return new Dimension(400, 500);
    }

    private void setTextFields()
    {
        int num = 30;  //If 19 or less, all components shown.
        String[] labelsNames =
        {
            "1", "2", "3", "4", "5", "6", "7", "8", "9", "10",
            "11", "12", "13", "14", "15", "16", "17", "18", "19", "20",
            "21", "22", "23", "24", "25", "26", "27", "28", "29", "30"
        };
        FieldsArray = new JTextField[num];
        LabelsArray = new JLabel[num];

        GroupLayout.ParallelGroup parallelGroupHoriz = layout.createParallelGroup();
        layout.setHorizontalGroup(layout.createSequentialGroup().addGroup(parallelGroupHoriz));
        for (int i = 0; i < num; i++)
        {
            System.out.println(i);
            LabelsArray[i] = new JLabel(labelsNames[i]);
            FieldsArray[i] = new JTextField(10);
            FieldsArray[i].setMaximumSize(new Dimension(200, 3));
            LabelsArray[i].setLabelFor(FieldsArray[i]);
            parallelGroupHoriz.addGroup(layout.createSequentialGroup()
                    .addComponent(LabelsArray[i])
                    .addComponent(FieldsArray[i]));
        }
        parallelGroupHoriz.addComponent(addRecordButton, GroupLayout.Alignment.CENTER);

        GroupLayout.SequentialGroup sequentialGroupVert = layout.createSequentialGroup();

        layout.setVerticalGroup(sequentialGroupVert);
        for (int i = 0; i < num; i++)
        {
            sequentialGroupVert.addGroup(layout.createParallelGroup().
                    addComponent(LabelsArray[i])
                    .addComponent(FieldsArray[i]));
        }
        sequentialGroupVert.addComponent(addRecordButton);

        for (int i = 0; i < num; i++)
        {
            layout.linkSize(SwingConstants.HORIZONTAL, LabelsArray[i], LabelsArray[0]);
        }
    }

    private void showDialog()
    {
        JOptionPane.showOptionDialog(null, scrollPane, "Update data",
                JOptionPane.DEFAULT_OPTION, JOptionPane.PLAIN_MESSAGE, null,
                null, null);
    }

    public static void main(String[] args)
    {
        DynamicGroupLayout d = new DynamicGroupLayout();
    }
}

Answer 1

如此相关的example所示，您可以覆盖视口的首选大小。

import java.awt.Dimension;
import java.awt.EventQueue;
import javax.swing.GroupLayout;
import javax.swing.JLabel;
import javax.swing.JOptionPane;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTextField;
import javax.swing.SwingConstants;

/**
 * @see https://stackoverflow.com/a/14858272/230513
 * @see https://stackoverflow.com/a/8504753/230513
 * @see https://stackoverflow.com/a/14011536/230513
 */
public class DynamicGroupLayout {

    private static final int NUM = 30;
    private JTextField[] fields = new JTextField[NUM];
    private JLabel[] labels = new JLabel[NUM];

    private JPanel create() {
        JPanel panel = new JPanel();
        GroupLayout layout = new GroupLayout(panel);
        panel.setLayout(layout);
        layout.setAutoCreateGaps(true);
        layout.setAutoCreateContainerGaps(true);
        GroupLayout.ParallelGroup parallel = layout.createParallelGroup();
        layout.setHorizontalGroup(layout.createSequentialGroup().addGroup(parallel));
        GroupLayout.SequentialGroup sequential = layout.createSequentialGroup();
        layout.setVerticalGroup(sequential);
        for (int i = 0; i < NUM; i++) {
            labels[i] = new JLabel(String.valueOf(i + 1), JLabel.RIGHT);
            fields[i] = new JTextField(String.valueOf("String " + (i + 1)));
            labels[i].setLabelFor(fields[i]);
            parallel.addGroup(layout.createSequentialGroup().
                addComponent(labels[i]).addComponent(fields[i]));
            sequential.addGroup(layout.createParallelGroup(GroupLayout.Alignment.BASELINE).
                addComponent(labels[i]).addComponent(fields[i]));
            layout.linkSize(SwingConstants.HORIZONTAL, labels[i], labels[0]);
        }
        return panel;
    }

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                final JPanel panel = new DynamicGroupLayout().create();
                JScrollPane jsp = new JScrollPane(panel) {
                    @Override
                    public Dimension getPreferredSize() {
                        return new Dimension(320, 240);
                    }
                };
                JOptionPane.showMessageDialog(null,
                    jsp, "Data", JOptionPane.PLAIN_MESSAGE);
            }
        });
    }
}