gridlayout not working with custom jpanel and jscrollpane; my jpanels get cut off

[Mark Brunson]

I'm trying to add my own implementation of jpanel to another jpanel, in a scrollpane, so that as it adds more it will make a list of them down the screen. Unfortunately I can't seem to put space between my jpanels; when I set the second two gridlayout parameters, parts of them get cut off (so that they appear shorter vertically). Any idea why this is happening or how to get around it?

(called from a method in a jframe class)

miniPanel = new JPanel();
		miniPanel.setLayout(new java.awt.GridLayout(100, 4,0,60));
		for(int i=0;i<900;i++)
			miniPanel.add(new CustomDrawing());
		scrollPane_1 = new JScrollPane(miniPanel);
		scrollPane_1.setBounds(27, 492, 767, 319);
		getContentPane().add(scrollPane_1);

custom drawing panel

public class CustomDrawing extends JPanel{
	Graphics dbGraphics;
	Image dbImage;
	public static void main(String[] args)
	{
		JFrame j=new JFrame();
		j.setSize(200, 200);
		j.setVisible(true);
		j.setLayout(new BorderLayout());
		j.add(new CustomDrawing());
	}
	public CustomDrawing()
	{
		dbImage = new BufferedImage(100,100, BufferedImage.TYPE_INT_RGB);
		dbGraphics=dbImage.getGraphics();
	}
	public void paint(Graphics g) {
		
		//System.out.println("visnetdisplay painting");
		/************************
		 * DO YOUR DRAWING HERE *
		 *  draw to dbGraphics  *
		 ************************/
		drawStuff();
				
		// update our screen
		update(g);
		if(dbGraphics==null)
		{
			System.err.println("DBGRAPHICS IS NULL");
		}
		else
		{
			super.paint(dbGraphics);
		}
	}
	public void drawStuff()
	{
		dbGraphics.setColor(Color.RED);
		dbGraphics.fillRect(0, 0, 30, 30);
	}
	public void update(Graphics g)
	{
		g.drawImage(this.dbImage, 0,0, this);
	}
}

[Michael Dunn]

as CustomDrawing() has no components, it possibly needs to have a preferredSize set

[Rob Spoor]

Welcome to the Ranch, Mark!

Your CustomDrawing instance never paints itself on the screen. You've overridden the paint method to draw to the BufferedImage's graphics object instead. That object will never be null though, as it's created in the CustomDrawing constructor and never set to null afterwards.

I suggest you change your code:
1) Call drawStuff() in the constructor. There is no need to do it in any painting method, as the painting methods may be called several times a minute. The contents will never change though, so once is enough.

2) Do not override update(Graphics).

3) Do not override paint(Graphics).

4) Override paintComponent(Graphics) like this:

protected void paintComponent(Graphics g)
{
    super.paintComponent(g); // don't forget this call
    g.drawImage(this.dbImage, 0, 0, this);
}

The preferred size issue probably still applies as well.

[Mark Brunson]

setPreferredSize does fix my issue, thanks! The reason for all the overridden methods in CustomDrawing is that I'm actually using a much larger, more complicated class that frequently updates instead, I just wrote this one to have something simple to represent the problem I was having without tons of irrelevant code.