Java: Override table cell renderer, but with default background and properties

Question

If you want to add a custom renderer, normally, you'd either extend some JComponent (like JLabel) and implement TableCellRenderer, or you'd extend DefaultTableCellRenderer. However, in either case, what I find is that the cell style is completely overridden.

What I'd really like is to be able to paint the default L&F background and then paint on top of it using other L&F defaults like foreground color and font.

So, here's what I tried to do. First, the class:

public class IntervalHeaderRenderer extends JLabel implements TableCellRenderer {

    private TableCellRenderer delegate;
    private Component component;

    public IntervalHeaderRenderer(TableCellRenderer defaultRenderer)
    {
        this.delegate = defaultRenderer;
    }

    @Override
    public Component getTableCellRendererComponent(JTable table, Object value,
                           boolean isSelected, boolean hasFocus, int row, int column)
    {
        component = delegate.getTableCellRendererComponent(table, value, isSelected, hasFocus, row, column);

        // Maybe override some settings.  
        // You could make the label bold, for instance.

        return component;
        // return this;
    }

    @Override
    public void paint(Graphics g) {
        // What I really want to do is paint the original component
        component.paint(g);
        // And then draw on top of it.
    }
}

And then I override the cell (header) renderer like this:

TableCellRenderer renderer = table.getTableHeader().getDefaultRenderer();
table.getColumnModel().getColumn(1).setHeaderRenderer(new IntervalHeaderRenderer(renderer));

I'm basically just following the suggestions here: TableCellRenderer, Part 2 - How To Create A Custom Renderer

If I return component, it renders as if I had overridden nothing. That is, I get the header with the label I had programmed with the chosen L&F background and style and everything. But, of course, there no way to render my stuff afterwards.

On the other hand, if I return this, then I get absolutely nothing. Mac native L&F gives me a white background, while Nimbus gives me a solid of some other color.

I'm clearly missing something. Are there other methods on the Component that I need to override and forward to the original? How does the default component get drawn if not by overriding paint? (I've also tried overriding paintComponent. No difference.)

Is there another way to do this? I've thought about trying to drop a native styled JPanel in there and then making a custom (transparent background) component its child, although I'm not sure about how to go about it, and I'm not really sure I'd get the native L&F table header background anyhow. In fact, I highly doubt I'd get the native header style, just the native JPanel style.

Basically, I need a custom table header (and separately, the cells too, actually), but I want to avoid messing too much with the native L&F.

Thanks!

Answer 1

You might look at the approach taken in updateUI() in SelectAllHeaderTest, as well as the helpful caveats in the accepted answer.

Addendum: By way of explanation, note that the header's appearance falls under the aegis of the host platform's corresponding UI delegate, usually derived from TableHeaderUI. You may want to confine your changes to the UIManager Defaults common to popular Look & Feel implementations. Also, don't override paint(). I would avoid overriding paintComponent(); and, if necessary, override paintIcon(), as shown in TableSorter.

Answer 2

Check the DefaultTableCellRenderer source code, there you will see how the default behavior reads the defaults colors like:

        fg = DefaultLookup.getColor(this, ui, "Table.dropCellForeground");
        bg = DefaultLookup.getColor(this, ui, "Table.dropCellBackground");