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javaswingjava-2d

Java 2D - JLabel only partially painted inside JList

I'm experimenting with 2D painting in Swing, and I'd like to paint a JLabel in the middle of an empty JList.
Thus I came up with:

public class MyJList<T> extends JList<T> {
  private final JLabel emptyLabel = new JLabel("Whatever");

  @Override
  public void paint(final Graphics g) {
    super.paint(g);

    if (getModel().getSize() == 0 && !emptyLabel.getText().isBlank()) {
      final var preferredSize = emptyLabel.getPreferredSize();
      final var x = (getWidth() - preferredSize.width) / 2;
      final var y = (getHeight() - preferredSize.height) / 2;
      final var g2 = (Graphics2D) g.create(x, y, preferredSize.width, preferredSize.height);

      try {
        emptyLabel.setBounds(0, 0, preferredSize.width, preferredSize.height);
        emptyLabel.paint(g2);
      } finally {
        g2.dispose();
      }
    }
  }
}

However when the text reaches the bounds of the list, it seems to get truncated:

enter image description here

If I increase the clipping rectangle width, the label is fully painted.
What am I doing wrong? Is this a good way to paint?

Complete minimal example:

class Main {
  public static void main(final String[] args) {
    final var myFrame = new MyFrame();
    myFrame.setVisible(true);
  }

  public static class MyFrame extends JFrame {
    public MyFrame() {
      super("Example");

      final var list = new MyJList<String>();

      final var contentPane = getContentPane();
      contentPane.setLayout(new BorderLayout());
      contentPane.add(list, BorderLayout.CENTER);

      pack();
      setMinimumSize(new Dimension(160, 200));
      setLocationRelativeTo(null);
    }
  }

  public static class MyJList<T> extends JList<T> {
    private final JLabel emptyLabel = new JLabel("Selezionare un oggetto");

    {
      emptyLabel.setEnabled(false);
    }

    @Override
    public void paint(final Graphics g) {
      super.paint(g);

      if (getModel().getSize() == 0) {
        final var preferredSize = emptyLabel.getPreferredSize();
        final var listBounds = getBounds();
        final var x = (listBounds.width - preferredSize.width) / 2;
        final var y = (listBounds.height - preferredSize.height) / 2;
        final var g2 = (Graphics2D) g.create(x, y, preferredSize.width, preferredSize.height);

        try {
          emptyLabel.setBounds(0, 0, preferredSize.width, preferredSize.height);
          emptyLabel.paint(g2);
        } finally {
          g2.dispose();
        }
      }
    }
  }
}
Solution

  • Text layout is tricky at the best of times, and the more you can avoid it, the better (IMHO).

    Personally, I avoid the custom paint route, but this is me, and try something a little more simpler.

    With the use of a PropertyChangeListener, to monitor when the ListModel changes, and a custom ListDataListener, to monitor when the ListModel itself changes, you can create a similar result.

    One addition here is the fact that I've wrapped the text in <html> tags, this will trigger the "word" wrapping.

    Example

    import java.awt.BorderLayout;
import java.awt.GridBagLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.beans.PropertyChangeEvent;
import java.beans.PropertyChangeListener;
import javax.swing.DefaultListModel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JList;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.ListModel;
import javax.swing.SwingUtilities;
import javax.swing.event.ListDataEvent;
import javax.swing.event.ListDataListener;

public class Test {

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

    public Test() {
        SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                JFrame frame = new JFrame();
                frame.add(new TestPane());
                frame.pack();
                frame.setVisible(true);
            }
        });
    }

    public class TestPane extends JPanel {

        private DefaultListModel<String> model = new DefaultListModel<String>();

        public TestPane() {
            setLayout(new BorderLayout());

            JPanel panel = new JPanel(new GridBagLayout());
            JButton add = new JButton("Add");
            JButton remove = new JButton("Remove");

            panel.add(add);
            panel.add(remove);

            MyList<String> myList = new MyList<>();
            myList.setModel(model);

            add(new JScrollPane(myList));
            add(panel, BorderLayout.SOUTH);

            add.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent evt) {
                    model.addElement("Hello");
                }
            });
            remove.addActionListener(new ActionListener() {
                @Override
                public void actionPerformed(ActionEvent evt) {
                    if (model.size() > 0) {
                        model.remove(0);
                    }
                }
            });
        }

    }

    public class MyList<T> extends JList<T> {

        final private ModelHandler modelHandler = new ModelHandler();

        final private JLabel emptyLabel = new JLabel("<html>Selezionare un oggetto</html>");

        public MyList() {
            emptyLabel.setHorizontalAlignment(JLabel.CENTER);
            setLayout(new BorderLayout());
            add(emptyLabel);
            emptyLabel.setVisible(false);
            addPropertyChangeListener("model", new PropertyChangeListener() {
                @Override
                public void propertyChange(PropertyChangeEvent evt) {
                    if ((evt.getOldValue() instanceof ListModel)) {
                        ListModel model = (ListModel) evt.getOldValue();
                        model.removeListDataListener(modelHandler);
                    }
                    if ((evt.getNewValue() instanceof ListModel)) {
                        ListModel model = (ListModel) evt.getNewValue();
                        model.addListDataListener(modelHandler);
                    }
                    updateEmptyLabel();
                }
            });
        }

        protected void updateEmptyLabel() {
            emptyLabel.setVisible(getModel().getSize() == 0);
        }

        protected class ModelHandler implements ListDataListener {

            @Override
            public void intervalAdded(ListDataEvent evt) {
                updateEmptyLabel();
            }

            @Override
            public void intervalRemoved(ListDataEvent evt) {
                updateEmptyLabel();
            }

            @Override
            public void contentsChanged(ListDataEvent evt) {
                updateEmptyLabel();
            }

        }

    }
}