arrange multiple JPanels with different heights

Question

Im trying to show multiple JPanels in a JScrollPane.

The Panels contain a header-subpanel with a collapse/expand button and a content-subpanel with a JTable and some JButtons.

The height of each Panel is determined by the size of a JTable inside the Panel.

If there arent enough JPanels to fill the JScrollPane, the remaining space should be empty.

My approach with BoxLayout works quite well, as long as there are enough Panels.

If i set TEST_NUMBER_OF_PANELS to 50, it behaves like excpeted. If i set TEST_NUMBER_OF_PANELS to 2, the Panel´s heights are adjusted to fill the whole scrollpane.

I use a JXCollapsiblePane from the swingx library as content-subpanel. If i collapse a Panel and there are just a few Panels visible the LayoutManager starts resizing the header-subpanel which should always stay the same size. (i guess thats a subsequent error of my incorrect usage of LayoutManager)

the following SSCCE compiles without any external libraries. i added "TODO: un/comment line" where i replaced the JXCollapsiblePane with JPanel. (import, initialisation, binding)

im not sure which LayoutManager fits best to arrange my Panels. i guess i could ditch some JPanels as well if i used the LayoutManager correctly.

thank you in advance

package test;

import java.awt.BorderLayout;
import java.awt.CardLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.util.Random;
import java.util.Vector;

import javax.swing.BorderFactory;
import javax.swing.BoxLayout;
import javax.swing.GroupLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.JTabbedPane;
import javax.swing.JTable;
import javax.swing.SwingConstants;
import javax.swing.SwingUtilities;
import javax.swing.table.DefaultTableModel;

// TODO: uncomment line
//import org.jdesktop.swingx.JXCollapsiblePane;

public class Test extends JFrame {
    private static final int TEST_NUMBER_OF_PANELS = 50;
    private static JTabbedPane tabbedPane = new JTabbedPane();
    Test() {
        this.setLayout(new BorderLayout());
        this.setSize(1050, 700);
        this.setMinimumSize(new Dimension(400,200));
        this.add(tabbedPane, BorderLayout.CENTER);

        tabbedPane.addTab("tab1", new TestTabContent());
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                new Test().setVisible(true);
            }
        });
    }

    private class TestTabContent extends JPanel {
        TestTabContent() {
            JPanel boxContainer = new JPanel();
            boxContainer.setLayout(new BoxLayout(boxContainer, BoxLayout.Y_AXIS));
            JScrollPane mainScrollPane = new JScrollPane(boxContainer);

            // create toolbar
            JPanel toolBar = new JPanel();
            toolBar.setLayout(new BorderLayout());

            //east
            JPanel InfoPanel = new JPanel();
            InfoPanel.setLayout(new BoxLayout(InfoPanel, BoxLayout.X_AXIS));
            InfoPanel.add(new JLabel("test: some info ..."));
            toolBar.add(InfoPanel, BorderLayout.WEST);
            //west
            JPanel viewOptionPanel = new JPanel();
            viewOptionPanel.setLayout(new BoxLayout(viewOptionPanel, BoxLayout.X_AXIS));
            viewOptionPanel.add(new JLabel("some controls.."));
            toolBar.add(viewOptionPanel, BorderLayout.EAST);

            // set main panel´s layout
            GroupLayout layout = new GroupLayout(this);
            this.setLayout(layout);
            layout.setHorizontalGroup(
                    layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                    .addComponent(toolBar, GroupLayout.DEFAULT_SIZE, GroupLayout.DEFAULT_SIZE, Short.MAX_VALUE)
                    .addComponent(mainScrollPane)
                    );
            layout.setVerticalGroup(
                    layout.createParallelGroup(GroupLayout.Alignment.LEADING)
                    .addGroup(layout.createSequentialGroup()
                            .addComponent(toolBar, GroupLayout.PREFERRED_SIZE, GroupLayout.DEFAULT_SIZE, GroupLayout.PREFERRED_SIZE)
                            .addGap(0, 0, 0)
                            .addComponent(mainScrollPane, GroupLayout.DEFAULT_SIZE, 413, Short.MAX_VALUE))
                    );

            // create controls 4 test ...
            for (int i = 0; i < TEST_NUMBER_OF_PANELS; i++) {
                TestPanel newTestPanel = new TestPanel();

                // seperator panels for spacing
                JPanel seperator = new JPanel(new BorderLayout());
                seperator.setBackground(Color.black);
                seperator.add(newTestPanel);

                boxContainer.add(seperator);
            }
        }
    }
    private class TestPanel extends JPanel { 
        //private static final Icon COLLAPSE_ICON = new ImageIcon(Test.class.getResource("images/collapse_1616.png"));
        //private static final Icon EXPAND_ICON = new ImageIcon(Test.class.getResource("images/expand_1616.png"));
        private JTable table;
        private DefaultTableModel tableModel;
        private JButton collapsingButton;

        // TODO: uncomment line
        //private JXCollapsiblePane collapsiblePane = new JXCollapsiblePane();
        // TODO: comment line
        private JPanel collapsiblePane = new JPanel();

        public TestPanel() {

            this.setLayout(new BorderLayout()); 

            this.setBorder(BorderFactory.createLineBorder(Color.BLACK));

            // container with boxLayout for collapsiblePane
            JPanel boxContainer = new JPanel();
            boxContainer.setLayout(new BoxLayout(boxContainer, BoxLayout.Y_AXIS));
            boxContainer.setBorder(BorderFactory.createMatteBorder(0, 1, 1, 1, Color.BLACK));

            // set table stuff
            tableModel = new DefaultTableModel();
            // column headers
            Vector<String> title = new Vector<String>();
            title.add("A");
            title.add("B");
            title.add("C");
            title.add("D");
            // some random data
            Random randomGenerator = new Random();
            int rnd = randomGenerator.nextInt(10) + 1;
            Vector<Vector<String>> data = new Vector<Vector<String>>();
            Vector<String> row = new Vector<String>();
            for (int i=0; i<rnd; i++) {
                row.add("1");
                row.add("2");
                row.add("3");
                row.add("4");
                data.add(row);
            }
            tableModel.setDataVector(data, title);
            table = new JTable(tableModel);

            boxContainer.add(table.getTableHeader(), BorderLayout.NORTH);
            boxContainer.add(table, BorderLayout.CENTER);

            // other controls / toolbar
            JPanel toolbar = new JPanel();
            toolbar.setLayout(new BorderLayout());

            // buttons to the right
            JPanel toolbarButtonGroup = new JPanel();
            toolbarButtonGroup.setLayout(new BoxLayout(toolbarButtonGroup, BoxLayout.X_AXIS));

            // Button1
            JButton button = new JButton("Button1");
            JPanel sepPanel = new JPanel();
            sepPanel.add(button);
            toolbarButtonGroup.add(sepPanel);

            // Button2
            button = new JButton("Button2");
            sepPanel = new JPanel();
            sepPanel.add(button);
            toolbarButtonGroup.add(sepPanel);

            // Button3
            button = new JButton("Button3");
            sepPanel = new JPanel();
            sepPanel.add(button);

            toolbarButtonGroup.add(sepPanel);

            toolbar.add(toolbarButtonGroup, BorderLayout.EAST);
            boxContainer.add(toolbar);

            JPanel subPanel = new JPanel();
            subPanel.setLayout(new BoxLayout(subPanel, BoxLayout.Y_AXIS));          

            // add panel with collapse/expand button
            JPanel buttonPanel = new JPanel(); 
            buttonPanel.setLayout(new BorderLayout());
            buttonPanel.setMaximumSize(new Dimension(Integer.MAX_VALUE, 24));

            collapsingButton = new JButton("foo"); // , COLLAPSE_ICON
            collapsingButton.setName("toggleButton");
            collapsingButton.setHorizontalAlignment(SwingConstants.LEFT);
            collapsingButton.setBorderPainted(false);
            collapsingButton.setFocusPainted(false);

            buttonPanel.add(collapsingButton, BorderLayout.CENTER); 
            buttonPanel.setBorder(BorderFactory.createLineBorder(Color.BLACK));

            subPanel.add(buttonPanel);

            collapsiblePane.setName("collapsiblePane"); 
            collapsiblePane.setLayout(new CardLayout()); 

            collapsiblePane.add(boxContainer, ""); 
            subPanel.add(collapsiblePane); 

            add(subPanel);

            // TODO: uncomment line
            //collapsingButton.addActionListener(collapsiblePane.getActionMap().get( 
            //      JXCollapsiblePane.TOGGLE_ACTION)); 
        } 
    } 
}

Answer 1

You may just encapsulate your panel into another layout which reduces size as much as possible (code inside TestTabContent()):

JPanel boxContainer = new JPanel();
boxContainer.setLayout(new BoxLayout(boxContainer, BoxLayout.Y_AXIS));

JPanel boxContainerOuter = new JPanel();
boxContainerOuter.setLayout(new BorderLayout());
boxContainerOuter.add(boxContainer, BorderLayout.NORTH);

JScrollPane mainScrollPane = new JScrollPane(boxContainerOuter);

In the code above the boxContainer is contained in another panel boxContainerOuter. Its layout and position (BoxLayout.NORTH) is chosen such that the outer container shrinks the panel included.