JList with EmptyBorder inside JScrollPane moves against my will

[Mack Wilmot]

I have been looking for a reason for this to no avail. I have a JList with an EmptyBorder (for some margin). It is in a JScrollPane. When there is a list entry that is wider than the viewport, I can click on the JList and if I move the mouse cursor any when clicking, the JList scrolls to the left, the width of the border, putting the text up next to the edge of the viewport again. This is rather annoying as it defeats the purpose of using the EmptyBorder for margin.

[Darryl Burke]

Post an SSCCE.

[Mack Wilmot]

Although I am using the free design in NetBeans, I generated the simplest case with a null layout and it behaves the same. This is the Windows L&F, but it does the same with Metal, Nimbus L&F.

package javaapplication1;

/**
 *
 * @author User06
 */
public class NewJFrame extends javax.swing.JFrame {

    /**
     * Creates new form NewJFrame
     */
    public NewJFrame() {
        initComponents();
    }

     @SuppressWarnings("unchecked")
    private void initComponents() {

        jScrollPane1 = new javax.swing.JScrollPane();
        jList1 = new javax.swing.JList();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        getContentPane().setLayout(null);

        jList1.setBorder(javax.swing.BorderFactory.createEmptyBorder(0, 4, 0, 0));
        jList1.setModel(new javax.swing.AbstractListModel() {
            String[] strings = { "Item 12345678910111213141516", "Item 2", "Item 3", "Item 4", "Item 5" };
            public int getSize() { return strings.length; }
            public Object getElementAt(int i) { return strings[i]; }
        });
        jScrollPane1.setViewportView(jList1);

        getContentPane().add(jScrollPane1);
        jScrollPane1.setBounds(140, 50, 70, 130);

        pack();
    }                  

    /**
     * @param args the command line arguments
     */
    public static void main(String args[]) {

        try {
            for (javax.swing.UIManager.LookAndFeelInfo info : javax.swing.UIManager.getInstalledLookAndFeels()) {
                if ("Windows".equals(info.getName())) {
                    javax.swing.UIManager.setLookAndFeel(info.getClassName());
                    break;
                }
            }
        } catch (ClassNotFoundException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (InstantiationException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (IllegalAccessException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        } catch (javax.swing.UnsupportedLookAndFeelException ex) {
            java.util.logging.Logger.getLogger(NewJFrame.class.getName()).log(java.util.logging.Level.SEVERE, null, ex);
        }


        java.awt.EventQueue.invokeLater(new Runnable() {
            public void run() {
                new NewJFrame().setVisible(true);
            }
        });
    }
               
    private javax.swing.JList jList1;
    private javax.swing.JScrollPane jScrollPane1;
        
}

[Darryl Burke]

Right. I see where that behavior is coming from. Take a look at line 2761 of BasicListUI.java, in the handler's mouseDragged(...) method.

                    list.scrollRectToVisible(cellBounds);

One way to get the behavior you desire is to use a custom renderer and set the left/right borders to the renderer, and the top/bottom borders to the JList.

import java.awt.Component;
import java.util.Random;
import javax.swing.*;
import javax.swing.border.Border;

public class EmptyBorderListDemo {

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

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

  public void makeUI() {
    String[] data = {"One", "Two", "Three", "Four", "Five",
      "Six", "Sevem", "Eight", "Nine", "Ten",
      "Eleven", "Twelve", "Thirteen", "Fourteen", "Fifteen",
      "Sixteen", "Seventeen", "Eighteen", "Nineteen", "Twenty"};
    int rand = new Random().nextInt(data.length);
    for (int i = 0; i < 5; i++) {
      data[rand] += " " + data[rand];
    }
    JList list = new JList(data);
    list.setCellRenderer(new DefaultListCellRenderer() {

      @Override
      public Component getListCellRendererComponent(JList list, Object value,
              int index, boolean isSelected, boolean cellHasFocus) {
        super.getListCellRendererComponent(list, value,
                index, isSelected, cellHasFocus);
        Border border = getBorder();
        if (border != null) {
          setBorder(BorderFactory
              .createCompoundBorder(BorderFactory.createEmptyBorder(0, 20, 0, 20),
              border));
        } else {
          setBorder(BorderFactory.createEmptyBorder(0, 20, 0, 20));
        }
        return this;
      }
    });
    list.setBorder(BorderFactory.createEmptyBorder(20, 0, 20, 0));

    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);
  }
}

You'll need to test whether that works with all LaFs.

[Mack Wilmot]

Thank you Darryl!

[Mack Wilmot]

It works on all the available L&F in NetBeans. I just added it to the form through the custom code properties, pre-adding for the JLabel (Lines 28-45), although I could add it in my controller. I see how it adds the border to the cell and no matter if I add it before or after adding a border to the JList, the code takes that into account. But in my case I don't need the border on the JList. Thanks again.

[Darryl Burke]

Mack Wilmot wrote:It works on all the available L&F in NetBeans.

Thank you for testing and reporting back.

[Mack Wilmot]

The check for a null border is not needed in my case. What it does is still detects a border, it is never null, even though I do not add one it still creates a compound border. This over pads the cell plus it causes a very thin dotted line to show around a cell when it is selected. So all I need is this code:

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

                setBorder(BorderFactory.createEmptyBorder(0, 8, 0, 8)); 

                return this;
            }
        });

        jScrollPane2.setViewportView(jListUserWordList);