JFrame

[Ben Buchli]

hi everybody,
I have a JFrame and added a JPanel to it, now how do I force shapes drawn to appear in this JPanel?
Thanks for the help!
Ben

[Ernest Friedman-Hill]

Write a subclass of JPanel, and use that instead of JPanel itself.

In your subclass, override paintComponent(Graphics).

In the first line of your override, call super.paintComponent(Graphics).

Then draw your shapes.

[Ben Buchli]

Thanks, Ernest.
It works...
how would I find that out without help???
now another question i have regarding panels. is it possible to add a ScrollPane to the Panel so that it becomes scrollable when the shapes are moved and not completely visible in the pane?
how would i do that?
thanks in advance
[ May 04, 2004: Message edited by: Ben Buchli ]

[Eddie Vanda]

Instead of adding your subclassed JPanel to the JFrame's Container instance (from getContentPane), use it as the argument to constructing a new JScrollPane and then add that JScrollPane instance to your Container instance.
So if your JPanel subclass is MyJPanel and the instance is myJPanel, then instead of using add (myJpanel), use:

JScrollPane jsp = new JScrollPane (myJpanel);
add (jsp);

[Ben Buchli]

Thanks, Eddie, thats what I did.
However, the problem is that when the shape gets drawn outside of the viewing window (which means it's not or only partially visible) then I want to have scroll bars available for the user to scroll.
How do I do that?? I have the scrollbars, but somehow, they stay disabled...
thanks,
Ben

[Craig Wood]

The idea is to override getPreferredSize in our drawing component and to keep it apprised of the changing width and height requirements during the drawing. As we update the width and height fields we call revalidate on the drawing component which tells the scrollpane we need more space.
Here's an example:

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.*;
import java.util.*;
import java.util.List;
import javax.swing.*;
import javax.swing.event.*;
 
public class DrawingTest
{
    public static void main(String[] args)
    {
        JFrame f = new JFrame();
        f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        f.getContentPane().add(new JScrollPane(new DrawingPanel()));
        f.setSize(400,400);
        f.setLocation(200,200);
        f.setVisible(true);
    }
}
 
class DrawingPanel extends JPanel
{
    List rectList;
    int width, height;
    final int PAD;
 
    public DrawingPanel()
    {
        rectList = new ArrayList();
        PAD = 15;
        DrawingAction action = new DrawingAction(this);
        addMouseListener(action);
        addMouseMotionListener(action);
        setBackground(Color.white);
    }
 
    protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D)g;
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                            RenderingHints.VALUE_ANTIALIAS_ON);
        for(int i = 0; i < rectList.size(); i++)
        {
            Rectangle r = (Rectangle)rectList.get(i);
            g2.draw(r);
        }
    }
 
    public Dimension getPreferredSize()
    {
        return new Dimension(width, height);
    }
 
    public List getList()
    {
        return rectList;
    }
 
    public void setWidth(int w)
    {
        this.width = w + PAD;
        revalidate();
    }
 
    public void setHeight(int h)
    {
        this.height = h + PAD;
        revalidate();
    }
}
 
class DrawingAction extends MouseInputAdapter
{
    DrawingPanel drawingPanel;
    Rectangle r;
    boolean dragging;
 
    public DrawingAction(DrawingPanel dp)
    {
        drawingPanel = dp;
        dragging = false;
    }
 
    public void mousePressed(MouseEvent e)
    {
        r = new Rectangle(e.getX(), e.getY(), 0, 0);
        List list = drawingPanel.getList();
        list.add(r);
        dragging = true;
    }
 
    public void mouseReleased(MouseEvent e)
    {
        dragging = false;
    }
 
    public void mouseDragged(MouseEvent e)
    {
        if(dragging)
        {
            Point p = e.getPoint();
            r.setFrame(r.x, r.y, p.x - r.x, p.y - r.y);
            if(p.x > drawingPanel.getWidth())
                drawingPanel.setWidth(p.x);
            if(p.y > drawingPanel.getHeight())
                drawingPanel.setHeight(p.y);
            drawingPanel.repaint();
        }
    }
}

[Ben Buchli]

Thanks a lot Craig,
seems to work...