How to change background color of list rows depending on value

[Dario]

Hi,
i have a short list of items and i'd like to set the background color of each row basing on the item type.
So i wrote a custom ListCellRenderer, but the final result is that the rows have all the same color, the one of the first item.
Here is my renderer:

public class DevicesRenderer extends Container implements ListCellRenderer {
    private Label nameLabel = new Label("");
    private Label typeLabel = new Label("");
  

    public DevicesRenderer() {
        setLayout(new BorderLayout());
        setCellRenderer(true);

        nameLabel.setUIID("ListTitle");
        typeLabel.setUIID("ListSubtitle");

        Container cnt = new Container(new BoxLayout(BoxLayout.Y_AXIS));
        cnt.addComponent(nameLabel);
        cnt.addComponent(typeLabel);
        addComponent(BorderLayout.WEST, cnt);
    }


    public Component getListCellRendererComponent(List list, Object value, int index, boolean isSelected) { 
        Device device = (Device) value;

        nameLabel.setText(device.getDescription());
        typeLabel.setText(device.getTypeId());

        int color = device.getColor();

        getUnselectedStyle().setBgColor(color);
        getSelectedStyle().setBgColor(color);
        getPressedStyle().setBgColor(color);
         
        return this;
    }

    public Component getListFocusComponent(List list) {
        return null;
    }

    public void repaint() {
    }
}

Thx for any help.

(Btw, is it ok that the getListCellRendererComponent method is invoked something like 700 times for a list of only 6 items?)

[Shai Almog]

Hi,
the renderer is invoked a lot to perform animations etc. so it will be called far more than what you would assume is necessary which is why its a very tricky component to create.
Use List.setMutableRendererBackgrounds(true) to enable this behavior.
We have an optimization in place that draws the background once for all renderers.

[dario....@archeometra.it]

Thx Shai, to make it work i applied the flag you suggested and also changed a couple of lines:

int color = device.getColor();
Style style = new Style(0, color, null, (byte)255);
setUnselectedStyle(style);
setSelectedStyle(style);
setPressedStyle(style);

[Shai Almog]

I would strongly recommend you don't do that. Replacing the style object is generally not a great idea but doing this in a renderer means you would be allocating dozens of objects per frame slowing down your app considerably.
Use getUnselectedStyle etc. and set the value on those styles.