JScrollPane scrolls beyond beginning when PAGE_UP key is pressed

Name: skT88420 Date: 09/24/99


In some cases, JScrollPane scrolls beyond the beginning
of the viewport contents when the PAGE_UP key is
pressed while the view position is at (0,0). Please
take a look at the test program below. If I press
PAGE_UP after starting the program, the viewport
contents disappear. They only become visible again
after hitting PAGE_DOWN or moving the scroll bar.
Maybe some kind of additional check is needed in
BasicScrollPaneUI.ScrollAction.

---

import java.awt.*;
import javax.swing.*;

public class JScrollPaneBug extends JDialog {
  public JScrollPaneBug() {
    super((Frame) null, "JScrollPane bug", true);
    
    JScrollPane scp = new JScrollPane();
    
    JPanel pnl = new JPanel();
    pnl.setLayout(new GridBagLayout());
    
      for (int i = 1; i <= 50; i++) {
        JTextField tf = new JTextField();
        tf.setText("Text field no." + i);
        pnl.add(tf, new GridBagConstraints(
          0, GridBagConstraints.RELATIVE, 1, 1, 1, 0,
          GridBagConstraints.CENTER, GridBagConstraints.HORIZONTAL,
          new Insets(0, 0, 0, 0), 0, 0));
      }
    
    scp.getViewport().add(pnl);
    
    getContentPane().add(scp);
    
    setSize(new Dimension(400, 300));
    setVisible(true);
  }
  
  public static void main(String args[]) {
    new JScrollPaneBug();
    System.exit(0);
  }
}
(Review ID: 95677)
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