Wrong background colors in Swing ListCellRenderer

Question

I'm currently trying to write a custom ListCellRenderer for a JList. Unfortunately, nearly all examples simply use DefaultListCellRenderer as a JLabel and be done with it; I needed a JPanel, however (since I need to display a little more info than just an icon and one line of text).

Now I have a problem with the background colors, specifically with the Nimbus PLAF. Seemingly the background color I get from list.getBackground() is white, but paints as a shade of gray (or blueish gray). Outputting the color I get yields the following:

Background color: DerivedColor(color=255,255,255 parent=nimbusLightBackground offsets=0.0,0.0,0.0,0 pColor=255,255,255

However, as can be seen, this isn't what gets painted.

It obviously works fine for the selected item. Currently I even have every component I put into the JPanel the cell renderer returns set to opaque and with the correct foreground and background colors—to no avail.

Any ideas what I'm doing wrong here?

ETA: Example code which hopefully runs.

public class ParameterListCellRenderer implements ListCellRenderer {
  @Override
  public Component getListCellRendererComponent(JList list, Object value,
      int index, boolean isSelected, boolean cellHasFocus) {
    // some values we need
    Border border = null;
    Color foreground, background;
    if (isSelected) {
      background = list.getSelectionBackground();
      foreground = list.getSelectionForeground();
    } else {
      background = list.getBackground();
      foreground = list.getForeground();
    }
    if (cellHasFocus) {
      if (isSelected) {
        border = UIManager.getBorder("List.focusSelectedCellHighlightBorder");
      }
      if (border == null) {
        border = UIManager.getBorder("List.focusCellHighlightBorder");
      }
    } else {
      border = UIManager.getBorder("List.cellNoFocusBorder");
    }

    System.out.println("Background color: " + background.toString());

    JPanel outerPanel = new JPanel(new BorderLayout());
    setProperties(outerPanel, foreground, background);
    outerPanel.setBorder(border);

    JLabel nameLabel = new JLabel("Factory name here");
    setProperties(nameLabel, foreground, background);
    outerPanel.add(nameLabel, BorderLayout.PAGE_START);

    Box innerPanel = new Box(BoxLayout.PAGE_AXIS);
    setProperties(innerPanel, foreground, background);
    innerPanel.setAlignmentX(Box.LEFT_ALIGNMENT);
    innerPanel.setBorder(BorderFactory.createEmptyBorder(0, 10, 0, 0));

    JLabel label = new JLabel("param: value");

    label.setFont(label.getFont().deriveFont(
        AffineTransform.getScaleInstance(0.95, 0.95)));
    setProperties(label, foreground, background);

    innerPanel.add(label);

    outerPanel.add(innerPanel, BorderLayout.CENTER);

    return outerPanel;
  }

  private void setProperties(JComponent component, Color foreground,
      Color background) {
    component.setOpaque(true);
    component.setForeground(foreground);
    component.setBackground(background);
  }
}

The weird thing is, if I do

if (isSelected) {
  background = new Color(list.getSelectionBackground().getRGB());
  foreground = new Color(list.getSelectionForeground().getRGB());
} else {
  background = new Color(list.getBackground().getRGB());
  foreground = new Color(list.getForeground().getRGB());
}

it magically works. So maybe the DerivedColor with nimbusLightBackground I'm getting there may have trouble?

It looks as if the containted JLabels would paint their own background. Guess you are getting the same result when you set their `opaque` to `false`? I think in that case we will need some example code to reproduce... — Peter Lang, May 07 '10 at 10:26
@Peter: Added code and another curiosity. Hope I got each part of the code that depends on our code here. — Joey, May 07 '10 at 10:46
While I can perfectly reproduce your problem and your workaround, I can't explain it. This forum thread talks about Nimbus ignoring `UIResource` (your background-color is a `DerivedColor$UIResource`), so this could be related. Not sure though :) — Peter Lang, May 07 '10 at 14:09
@Peter: Ok, I think this question leads a little into the wrong direction anyway. At least the only answer I got seems to be about how to specifically cater for the Nimbus LAF. I think the whole point of the PLAF system was that you can swap looks easily so I was more on the lookout for a good, sensible way of implementing a ListCellRenderer. Sadly, even a tutorial by one of the Swing developers makes flawed assumptions and ignores things. — Joey, May 07 '10 at 20:23

score 3 · Answer 1 · edited May 23 '17 at 12:09

JPanels default to opaque=true while jLabels default to opaque=false.

So, when a DefaultCellRender uses a JLabel, it gets the background of its parent.

Try just setting opaque to false on your panel.

Update:

Nimbus is using its own custom ListCellRenderer. I've found 2 mentions of working around it, one here on SO and one in Google's code repository (look for UpdateUI and NimbusCellRenderer).

Wrong background colors in Swing ListCellRenderer

1 Answers1