JScrollPane doesn't work.

[colin shuker]

Hi there, I'm trying to get an image drawn from within a JPanels' paintComponent(Graphics g) method inside a JScrollPane.

The Drawer object (drawer) extends JPanel, and has size 800 by 800.
This has an image also 800 by 800.

The JFrame class is shown here:

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

public class Main extends JFrame
{
    Drawer drawer;
    JPanel panel;
    JScrollPane jsp;
    
    public Main()
    {       
        drawer=new Drawer();
        drawer.setSize(800,800);
        
        jsp=new JScrollPane(drawer,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        jsp.setSize(400,400);
        jsp.setLocation(0,0);
        
        panel=new JPanel();
        panel.setSize(400,400);
        panel.setLayout(null);
        panel.add(jsp);
        
        
        this.setSize(500,500);
        this.getContentPane().add(panel,BorderLayout.CENTER);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
        
    }
    
    public static void main(String[] args)
    {
        new Main();
       
    }   
}

But what happens is, I can only see top left corner of image, and there are no ScrollBars present to move the image around inside of the JScrollPane jsp object.

Can anyone help me?
Thanks

[Michael Dunn]

you seem to be mixing the way to size:
null - setSize(..)
layoutManager - setPreferredSize(..)

(changed Drawer() to a JPanel with border)

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

class Main extends JFrame
{
    //Drawer drawer;
    JPanel drawer;
    JPanel panel;
    JScrollPane jsp;
 
    public Main()
    {
        //drawer=new Drawer();
        drawer=new JPanel();
        drawer.setBorder(new javax.swing.border.LineBorder(Color.BLACK,1));
        //drawer.setSize(800,800);
        drawer.setPreferredSize(new Dimension(800,800));
 
        jsp=new JScrollPane(drawer,JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);
        jsp.setSize(400,400);
        //jsp.setPreferredSize(new Dimension(400,400));
        jsp.setLocation(0,0);
 
        panel=new JPanel();
        //panel.setSize(400,400);
        panel.setPreferredSize(new Dimension(400,400));
        panel.setLayout(null);
        panel.add(jsp);
 

        this.setSize(500,500);
        this.getContentPane().add(panel,BorderLayout.CENTER);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setVisible(true);
 
    }
 
    public static void main(String[] args)
    {
        new Main();
 
    }
}

[colin shuker]

AMAZING, very fast too!!!

All I did was change drawer.setSize(...) to preferredSize(...)
And that worked

Don't know what the difference is, I'll look into it.

Thanks again!

[T Eakins]

For those who came across this (as I did), wanted to post a follow-on solution. The code above works because there is no layout manager, which is uncommon for larger projects. Here's the same block using a common layout manager, MigLayout (not using any of its bells and whistles), and the SwingX implementation of JXPanel. Note that JXPanel can be easily replaced with JPanel, just remove the additional lines that tell the panel not to recalculate its size dynamically, but to enforce the scrollable region.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;

import javax.swing.JFrame;
import javax.swing.JScrollPane;

import net.miginfocom.swing.MigLayout;

import org.jdesktop.swingx.JXPanel;

public class TestScroll extends JFrame {
    JXPanel goalPanel;
    JXPanel viewPanel;
    JScrollPane jsp;

    public TestScroll() {
        goalPanel = new JXPanel();
        MigLayout ml1 = new MigLayout("insets 0", "[pref!]", "[pref!]");
        goalPanel.setLayout(ml1);
        goalPanel.setScrollableTracksViewportHeight(false);  //JXPanel specific
        goalPanel.setScrollableTracksViewportWidth(false);   //JXPanel specific
        goalPanel.setBorder(new javax.swing.border.LineBorder(Color.BLACK, 5));
        goalPanel.setPreferredSize(new Dimension(600, 600));

        jsp = new JScrollPane(goalPanel, JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                JScrollPane.HORIZONTAL_SCROLLBAR_AS_NEEDED);

        viewPanel = new JXPanel();
        MigLayout ml2 = new MigLayout();
        viewPanel.setLayout(ml2);
        viewPanel.add(jsp);

        this.setSize(new Dimension(400, 400));  //JFrame
        this.getContentPane().add(viewPanel, BorderLayout.CENTER);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        this.setLocationRelativeTo(null);

        this.setVisible(true);
    }

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

}