Tabs at fixed positions in JTabbedPane or in one row

Question

In our application that has a JTabbedPane with unlimited tabs, when the width of the tabs exceeds the tabbed pane's width, the tabs start wrapping into several rows. When you then click on a tab in one of the upper rows, the complete row comes down and to the foreground. For users who click around between several tabs, it's highly confusing as it's not possible to keep track of the tab order.

How can I either - nail the tabs to fixed positions while bringing their contents to the front (though this would optically corrupt the tab metaphor but I don't care), or - limit the number of rows to one (so the tabs get very narrow instead of wrapping)?

Answer 1

After some hours of research I have finally found a clean solution.

First, figure out which UI class you are using. Put the following code after you initialize the L&F with UIManager.setLookAndFeel():

for (Map.Entry<Object, Object> entry : UIManager.getDefaults().entrySet()) {
    boolean isStringKey = entry.getKey().getClass() == String.class ;
    String key = isStringKey ? ((String) entry.getKey()):"";   
    if (key.equals("TabbedPaneUI")) {
        System.out.println(entry.getValue());
    }
}

In my case, it prints com.sun.java.swing.plaf.windows.WindowsTabbedPaneUI. If you are using a different L&F, this may be another class (or even if you are using another OS, if you take the OS default).

Next, just instantiate that class (which extends BasicTabbedPaneUI), and override the problematic method:

WindowsTabbedPaneUI jtpui = new WindowsTabbedPaneUI() {
    @Override protected boolean shouldRotateTabRuns(int i) {
        return false;
    }
};

If eclipse does not recognize the class, and gives you an "access restriction" error if you type the full name of the class, see this question: Access restriction: The type 'Application' is not API (restriction on required library rt.jar)

Finally, just set that UI for your JTabbedPane:

JTabbedPane jtp = new JTabbedPane();
jtp.setUI(jtpui);

However, there is a problem: some L&F don't take into account the non-scrolling of tabs rows, and it turns out ugly.

To fix this (I only tested on the Windows L&F), add the following immediately after initializing the L&F: UIManager.getDefaults().put("TabbedPane.tabRunOverlay", 0);

Answer 2

Really quick and dirty (definitely needs improvements and changes), but I would imagine that something like that could work for you (but is not a JTabbePane):

import java.awt.BorderLayout;
import java.awt.Component;
import java.awt.Container;
import java.awt.Dimension;
import java.awt.FlowLayout;
import java.awt.Insets;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.ArrayList;
import java.util.List;

import javax.swing.JButton;
import javax.swing.JComponent;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingUtilities;

public class Test {

    /**
     * FlowLayout subclass that fully supports wrapping of components.
     */
    public static class WrapLayout extends FlowLayout {
        private Dimension preferredLayoutSize;

        /**
         * Constructs a new <code>WrapLayout</code> with a left alignment and a
         * default 5-unit horizontal and vertical gap.
         */
        public WrapLayout() {
            super();
        }

        /**
         * Constructs a new <code>FlowLayout</code> with the specified alignment
         * and a default 5-unit horizontal and vertical gap. The value of the
         * alignment argument must be one of <code>WrapLayout</code>,
         * <code>WrapLayout</code>, or <code>WrapLayout</code>.
         * 
         * @param align
         *            the alignment value
         */
        public WrapLayout(int align) {
            super(align);
        }

        /**
         * Creates a new flow layout manager with the indicated alignment and
         * the indicated horizontal and vertical gaps.
         * <p>
         * The value of the alignment argument must be one of
         * <code>WrapLayout</code>, <code>WrapLayout</code>, or
         * <code>WrapLayout</code>.
         * 
         * @param align
         *            the alignment value
         * @param hgap
         *            the horizontal gap between components
         * @param vgap
         *            the vertical gap between components
         */
        public WrapLayout(int align, int hgap, int vgap) {
            super(align, hgap, vgap);
        }

        /**
         * Returns the preferred dimensions for this layout given the
         * <i>visible</i> components in the specified target container.
         * 
         * @param target
         *            the component which needs to be laid out
         * @return the preferred dimensions to lay out the subcomponents of the
         *         specified container
         */
        @Override
        public Dimension preferredLayoutSize(Container target) {
            return layoutSize(target, true);
        }

        /**
         * Returns the minimum dimensions needed to layout the <i>visible</i>
         * components contained in the specified target container.
         * 
         * @param target
         *            the component which needs to be laid out
         * @return the minimum dimensions to lay out the subcomponents of the
         *         specified container
         */
        @Override
        public Dimension minimumLayoutSize(Container target) {
            Dimension minimum = layoutSize(target, false);
            minimum.width -= getHgap() + 1;
            return minimum;
        }

        /**
         * Returns the minimum or preferred dimension needed to layout the
         * target container.
         * 
         * @param target
         *            target to get layout size for
         * @param preferred
         *            should preferred size be calculated
         * @return the dimension to layout the target container
         */
        private Dimension layoutSize(Container target, boolean preferred) {
            synchronized (target.getTreeLock()) {
                // Each row must fit with the width allocated to the containter.
                // When the container width = 0, the preferred width of the
                // container
                // has not yet been calculated so lets ask for the maximum.

                int targetWidth = target.getSize().width;

                if (targetWidth == 0) {
                    targetWidth = Integer.MAX_VALUE;
                }

                int hgap = getHgap();
                int vgap = getVgap();
                Insets insets = target.getInsets();
                int horizontalInsetsAndGap = insets.left + insets.right + hgap * 2;
                int maxWidth = targetWidth - horizontalInsetsAndGap;

                // Fit components into the allowed width

                Dimension dim = new Dimension(0, 0);
                int rowWidth = 0;
                int rowHeight = 0;

                int nmembers = target.getComponentCount();

                for (int i = 0; i < nmembers; i++) {
                    Component m = target.getComponent(i);

                    if (m.isVisible()) {
                        Dimension d = preferred ? m.getPreferredSize() : m.getMinimumSize();

                        // Can't add the component to current row. Start a new
                        // row.

                        if (rowWidth + d.width > maxWidth) {
                            addRow(dim, rowWidth, rowHeight);
                            rowWidth = 0;
                            rowHeight = 0;
                        }

                        // Add a horizontal gap for all components after the
                        // first

                        if (rowWidth != 0) {
                            rowWidth += hgap;
                        }

                        rowWidth += d.width;
                        rowHeight = Math.max(rowHeight, d.height);
                    }
                }

                addRow(dim, rowWidth, rowHeight);

                dim.width += horizontalInsetsAndGap;
                dim.height += insets.top + insets.bottom + vgap * 2;

                // When using a scroll pane or the DecoratedLookAndFeel we need
                // to
                // make sure the preferred size is less than the size of the
                // target containter so shrinking the container size works
                // correctly. Removing the horizontal gap is an easy way to do
                // this.

                Container scrollPane = SwingUtilities.getAncestorOfClass(JScrollPane.class, target);

                if (scrollPane != null) {
                    dim.width -= hgap + 1;
                }

                return dim;
            }
        }

        /*
         *  A new row has been completed. Use the dimensions of this row
         *  to update the preferred size for the container.
         *
         *  @param dim update the width and height when appropriate
         *  @param rowWidth the width of the row to add
         *  @param rowHeight the height of the row to add
         */
        private void addRow(Dimension dim, int rowWidth, int rowHeight) {
            dim.width = Math.max(dim.width, rowWidth);

            if (dim.height > 0) {
                dim.height += getVgap();
            }

            dim.height += rowHeight;
        }
    }

    public static class MyTabbedPane extends JPanel {
        private JPanel buttonPanel;
        private JPanel currentview;

        private Tab currentTab;

        private class Tab {
            String name;
            JComponent component;
        }

        private List<Tab> tabs = new ArrayList<Tab>();

        public MyTabbedPane() {
            super(new BorderLayout());
            buttonPanel = new JPanel(new WrapLayout());
            currentview = new JPanel();
            add(buttonPanel, BorderLayout.NORTH);
            add(currentview);
        }

        public void addTab(String name, JComponent tabView, int index) {
            if (index < 0 || index > tabs.size()) {
                throw new IllegalArgumentException("Index out of bounds");
            }
            final Tab tab = new Tab();
            tab.component = tabView;
            tab.name = name;
            tabs.add(index, tab);
            JButton b = new JButton(name);
            b.addActionListener(new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    setCurrentTab(tab);
                }

            });
            buttonPanel.add(b, index);
            buttonPanel.validate();
        }

        public void removeTab(int i) {
            Tab tab = tabs.remove(i);

            if (tab == currentTab) {
                if (tabs.size() > 0) {
                    if (i < tabs.size()) {
                        setCurrentTab(tabs.get(i));
                    } else {
                        setCurrentTab(tabs.get(i - 1));
                    }
                } else {
                    setCurrentTab(null);
                }
            }
            buttonPanel.remove(index);
        }

        void setCurrentTab(final Tab tab) {
            if (currentTab == tab) {
                return;
            }
            if (currentTab != null) {
                currentview.remove(currentTab.component);
            }
            if (tab != null) {
                currentview.add(tab.component);
            }
            currentTab = tab;
            currentview.validate();
        }
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame();
        MyTabbedPane tabbedPane = new MyTabbedPane();
        for (int i = 0; i < 100; i++) {
            tabbedPane.addTab("Button " + (i + 1), new JLabel("Dummy Label " + (i + 1)), i);
        }
        frame.add(tabbedPane);
        frame.pack();
        frame.setSize(new Dimension(1000, 800));
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

}

The WrapLayout was taken from another post on SO.