JScrollPane problem

[Eoin Mac Aoidh]

Hi all,
I am having a bit of trouble making a window that will provide scroll capabilities and contain a JPanel.
My code works fine for creating a window to provide scroll capabilities for a JLabel that is too big for the window (Just not for a panel, and I cant figure out why!!!)

Heres what Ive got:

    
import ...all the required imports...
 
public class TimeLineWindow extends JFrame {
           
           JFrame frame = new JFrame("Timeline Window Display");
 
           private JPanel mypanel;
               
 
 public TimeLineWindow () {
 

           mypanel=new JPanel();
           mypanel.setLayout(null);
           mypanel.setBackground(Color.red);
           mypanel.setBounds(2,2,500,500);
 
   Icon ii = new ImageIcon("C:/workspace/sample.jpg");
   JLabel displayLabel = new JLabel(ii);
   //heres the problem: displays the label fine, but wont work for mypanel!
     JScrollPane scrollPane = new JScrollPane(displayLabel);
  // JScrollPane scrollPane = new JScrollPane(mypanel);
 
   frame.getContentPane().add(scrollPane, BorderLayout.CENTER);
   frame.setSize(400, 400);
   frame.setVisible(true);
 }
 

Is it just not possible to do this for a panel?
I would be delighted with any pointers.
Many thanks,

Eoin.

[Craig Wood]

ScrollPanes need to know the preferredSize of their child/view components. If the child/view component does not have any children then its layout manager, null here, will not have a preferredSize computed to answer the parent containers call for it as part of the layout process. So you have to provide this information for the component so the parent/scrollPane can get it in when it asks for it.

import java.awt.*;
import javax.swing.*;
 
public class TLW extends JFrame {
 
    public TLW() {
        JPanel mypanel=new JPanel();
        mypanel.setLayout(null);
        mypanel.setBackground(Color.red);
        mypanel.setBounds(2,2,500,500);
        mypanel.setPreferredSize(mypanel.getSize());
 
        Icon ii = new ImageIcon(//"C:/workspace/sample.jpg");
                                "images/hawk.jpg");
        JLabel displayLabel = new JLabel(ii);
        //heres the problem: displays the label fine, but wont work for mypanel!
//        JScrollPane scrollPane = new JScrollPane(displayLabel);
        JScrollPane scrollPane = new JScrollPane(mypanel);
 
        getContentPane().add(scrollPane, BorderLayout.CENTER);
        setSize(400, 400);
        setVisible(true);
    }
 
    public static void main(String[] args) {
        new TLW();
    }
}