How can I set a JLabel's background and border

问题:

I want to recreate a table header looks using JLabel. The look and feel of the JLabel needs to be exactly like the JTableHeader would be, specified by the system.

This is what I have tried so far:

JLabel header = new JLabel("Title");
header.setOpaque(true);
header.setBackground(UIManager.getColor(new JTableHeader().getBackground()));
header.setBorder(UIManager.getBorder(new JTableHeader().getBorder()));

But, the UIManager returns null for the color and border.

Any ideas?

This is how I set the Look and Feel:

javax.swing.UIManager.setLookAndFeel(javax.swing.UIManager.getSystemLookAndFeelClassName());

回答1:

There are more issues involved then just getting the color and border of the table header. Each cell/column is rendered by a TableCellRenderer meaning that the values return by the UIManager may be ignored...

For example, the following renders the JTableHeader and applies border/background to a JLabel based on values returned by the UIManager under the Window's Look and Feel...

As you can see, there's quite a difference between them

How ever, if all you're interested in is display a "group header" of some kind over the top of another component on a scroll pane, you could simply add a JTableHeader to the scroll panes column view directly...

public class TestHeader {

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

    public TestHeader() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                TableColumnModel model = new DefaultTableColumnModel();
                final TableColumn column = new TableColumn(0, 250);
                column.setHeaderValue("Test");
                model.addColumn(column);

                JTableHeader header = new JTableHeader();
                header.setColumnModel(model);

                final JTextArea textArea = new JTextArea();

                JScrollPane scrollPane = new JScrollPane(textArea);
                scrollPane.setColumnHeaderView(header);

                textArea.addComponentListener(new ComponentAdapter() {
                    @Override
                    public void componentResized(ComponentEvent e) {
                        column.setWidth(textArea.getWidth());
                    }
                });

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(scrollPane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }
}

UPDATED

public class TestHeader {

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

    public TestHeader() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                } catch (ClassNotFoundException ex) {
                } catch (InstantiationException ex) {
                } catch (IllegalAccessException ex) {
                } catch (UnsupportedLookAndFeelException ex) {
                }

                TableColumnModel model = new DefaultTableColumnModel();
                final TableColumn column = new TableColumn(0, 250);
                column.setHeaderValue("I don't see the problem");
                model.addColumn(column);

                final JTableHeader header = new JTableHeader();
                header.setColumnModel(model);

                DefaultTableModel tm = new DefaultTableModel(new Object[]{"A", "B", "C"}, 0);
                tm.addRow(new Object[]{"1", "2", "3", "4"});
                tm.addRow(new Object[]{"5", "6", "7", "8"});
                tm.addRow(new Object[]{"9", "10", "11", "12"});
                tm.addRow(new Object[]{"13", "14", "15", "16"});
                final JTable table = new JTable(tm);

                final JScrollPane scrollPane = new JScrollPane(table);
                /**
                 * For some reason, the header isn't being applied as soon as the
                 * table is added to the scroll pane, so we need to jump our next
                 * request to the end of the of event queue so that it will
                 * occur some time in the future
                 */
                SwingUtilities.invokeLater(new Runnable() {
                    @Override
                    public void run() {
                        scrollPane.setColumnHeaderView(header);
                    }

                });

                table.addComponentListener(new ComponentAdapter() {
                    @Override
                    public void componentResized(ComponentEvent e) {
                        column.setWidth(table.getWidth());
                    }

                });

                JFrame frame = new JFrame();
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.setLayout(new BorderLayout());
                frame.add(scrollPane);
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }

        });
    }

}

回答2:

Try taking the defaults from UIManager:

Color color = UIManager.getColor("TableHeader.background");
Border border = UIManager.getBorder("TableHeader.CellBorder");

回答3:

You need to set a look and feel for the application before trying:

header.setBackground(UIManager.getColor(new JTableHeader().getBackground()));
header.setBorder(UIManager.getBorder(new JTableHeader().getBorder()));

you should set a look and feel first like so:

  try {
    for (LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
        if ("Nimbus".equals(info.getName())) {
            UIManager.setLookAndFeel(info.getClassName());
            break;
        }
    }
} catch (Exception e) {
    // If Nimbus is not available, you can set the GUI to another look and feel.
}

Here is an example:

import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.SwingUtilities;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.table.JTableHeader;

public class Test {

    public Test() {
        initComponents();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    //set nimbus look and feel
                    for (UIManager.LookAndFeelInfo info : UIManager.getInstalledLookAndFeels()) {
                        if ("Nimbus".equals(info.getName())) {
                            UIManager.setLookAndFeel(info.getClassName());
                            break;
                        }
                    }
                } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException e) {
                    e.printStackTrace();
                }

                new Test();
            }
        });
    }

    private void initComponents() {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        JLabel header = new JLabel("Title");
        header.setBackground(UIManager.getColor(new JTableHeader().getBackground()));
        header.setBorder(UIManager.getBorder(new JTableHeader().getBorder()));

        frame.add(header);

        frame.pack();
        frame.setVisible(true);
    }
}

回答4:

I figured I'll create a JTable without any rows and place a JTextPane right underneath. And it works like charm.

JTextPane textPane = new JTextPane();
JPanel panel = new JPanel(new BorderLayout());

JTable table = new JTable(0, 1);
table.setPreferredScrollableViewportSize(new Dimension(600, 0));
JScrollPane js = new JScrollPane(table)

panel.add(js, BorderLayout.NORTH);
panel.add(new JScrollPane(textPane),BorderLayout.CENTER);