ListCellRenderer

[Dawid Skrzypczynski]

Hi,
I have a JList and if the cursor is in the cells that i want to change his background. My code:

class MyCellRenderer extends JLabel implements ListCellRenderer, MouseListener {
	private static final long serialVersionUID = 1L;

	@Override
	public Component getListCellRendererComponent(JList list, 
											      Object value,
											      int index, 
											      boolean isSelected,
											      boolean cellHasFocus) {
		setBackground(Color.green);
		setText("test");
		setOpaque(true);
		return this;
	}

	@Override
	public void mouseClicked(MouseEvent e) {
		// TODO Auto-generated method stub
		
	}
	@Override
	public void mouseEntered(MouseEvent e) {
		setBackground(Color.red);	
	}
	@Override
	public void mouseExited(MouseEvent e) {
		// TODO Auto-generated method stub
		
	}
	@Override
	public void mousePressed(MouseEvent e) {
		// TODO Auto-generated method stub
		
	}
	@Override
	public void mouseReleased(MouseEvent e) {
		// TODO Auto-generated method stub
		
	}	
}

Doesn't work... the cells has green background even if the cursor is in the cells.

p.s. Sorry for my English

[Luigi Plinge]

I'm guessing, but could try calling repaint() and revalidate(), or one or the other, after changing the background colour.

[Campbell Ritchie]

Don't know. But it looks like something which would sit better on our GUIs forum, so I shall move it.

[Dawid Skrzypczynski]

still the same...

[Luigi Plinge]

Instead of implementing MouseListener here, how about giving your JList a MouseListener (prefer composition over inheritance). You probably need to repaint the JList rather than this cell renderer. Also, I would extend a MouseAdapter rather than a MouseListener - it's easier.

[Darryl Burke]

Notice that one of the parameters to the getListCellRendererComponent(...) method is "boolean isSelected' ... then think what you can do with that.

edit:It's usually more convenient to extend DefaultListCellRenderer than to implement ListCellRenderer. But for merely changing background/selection background colors, you don't need to extend or implement anything -- just use the methods available in the JList API. Moreover, renderers aren't added to any component hierarchy so can't respond to input events. And in any case, implementing MouseListener in a lass extending JLabel doesn't automagically add the class as its own MouseListener, without code that explicitly does just that.

Finally, do you really want all the cells in the JList to display the word "test"?

@Luigi: No. Those method calls are relevant when adding/removing components to/from an already visible container.

[Dawid Skrzypczynski]

Darryl
I want to get the same effect what you have if you click start in the Windows and moving the cursor. IsSelected returns true if i click on the item but this is not that i want

[Dawid Skrzypczynski]

This code is just short example. The finally code will be more complicated: besides the text i set icon ect.

[Darryl Burke]

So you want a 'hover' effect?

import java.awt.Color;
import java.awt.Component;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import javax.swing.*;

public class HoverListDemo {

  public static void main(String[] args) throws Exception {
    SwingUtilities.invokeLater(new Runnable() {

      @Override
      public void run() {
        new HoverListDemo().makeUI();
      }
    });
  }

  public void makeUI() {
    Object[] data = {
      "One",
      "Two",
      "Three",
      "Four",
      "Five",};
    JList list = new JList(data);
    HoverListCellRenderer renderer = new HoverListCellRenderer();
    list.setCellRenderer(renderer);
    list.addMouseListener(renderer.getHandler(list));
    list.addMouseMotionListener(renderer.getHandler(list));

    JFrame frame = new JFrame();
    frame.add(new JScrollPane(list));

    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.setSize(400, 400);
    frame.setLocationRelativeTo(null);
    frame.setVisible(true);
  }
}

class HoverListCellRenderer extends DefaultListCellRenderer {

  private static final Color HOVER_COLOR = Color.YELLOW;
  private int hoverIndex = -1;
  private MouseAdapter handler;

  @Override
  public Component getListCellRendererComponent(JList list, Object value, int index, boolean isSelected, boolean cellHasFocus) {
    super.getListCellRendererComponent(list, value, index, isSelected, cellHasFocus);

    if (!isSelected) {
      setBackground(index == hoverIndex
              ? HOVER_COLOR : list.getBackground());
    }
    return this;
  }

  public MouseAdapter getHandler(JList list) {
    if (handler == null) {
      handler = new HoverMouseHandler(list);
    }
    return handler;
  }

  class HoverMouseHandler extends MouseAdapter {

    private final JList list;

    public HoverMouseHandler(JList list) {
      this.list = list;
    }

    @Override
    public void mouseExited(MouseEvent e) {
      setHoverIndex(-1);
    }

    @Override
    public void mouseMoved(MouseEvent e) {
      int index = list.locationToIndex(e.getPoint());
      setHoverIndex(list.getCellBounds(index, index).contains(e.getPoint())
              ? index : -1);
    }

    private void setHoverIndex(int index) {
      if (hoverIndex == index) return;
      hoverIndex = index;
      list.repaint();
    }
  }
}

[Dawid Skrzypczynski]

yes this is it
Thanks!

[Darryl Burke]

Note that the code I posted has scope for improvement. For example, now that I've thought about it some more, I should pass the JList to the constructor of the outer renderer class and construct the handler and add the listeners in that constructor. In the get...Component method I would check that the passed-in JList is the same list, and if not then throw an exception.

Doc comments should mention that this renderer implementation can't be shared between lists.