Can't Get ScrollBar to Show

[Ted Newholm]

Hi,
I have an array of TextAreas. The number of TextAreas is such that not all of them are visible. I would like to add a scroll bar so I can scroll all of them into view. I've tried various ways but none worked.
The following is a code stub that produces the textareas but doesn't show a scrollbar. Appreciate any help. Thanks.

import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
import java.util.*;

public class Form extends JFrame implements ActionListener
{
	JTextArea[] txa = new JTextArea[1200];
	JScrollPane scr = new JScrollPane();

	public Form()
	{
		scr.setLayout(null);
		scr.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

		int num = 0;
		int row = 25;
		int col = 100;
		Color bg = new Color(255, 255, 200);
		Color fg = new Color(0, 0, 255);

		for (int r = 0; r < row * 100; r+=row)
		{
			for (int c = 0; c < col * 12; c+=col)
			{
				txa[num] = new JTextArea();
				scr.add(txa[num]);
				txa[num].setBounds(c, r, col, row);
				txa[num].setBorder(BorderFactory.createLineBorder(Color.black));
				txa[num].setBackground(bg);
				txa[num].setForeground(fg);
				num++;
			}
		}
		add(scr);
		scr.setVisible(true);
	}

	public static void main(String[] args)
	{
		Form f = new Form();
		f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
		f.setSize(1200, 5000);
		f.setTitle("Form");
		f.setResizable(false);
		f.setLocation(0, 0);
		f.setVisible(true);
	}

	public void actionPerformed(ActionEvent e)
	{
	}
}

[Michael Dunn]

probably easier ways, but this seems to work OK.

import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import java.text.*;
import java.util.*;

class Form extends JFrame implements ActionListener
{
  JTextArea[] txa = new JTextArea[1200];
  JScrollPane scr = new JScrollPane();

  public Form()
  {
//scr.setLayout(null);
scr.setPreferredSize(new Dimension(1200,500));
    scr.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_ALWAYS);

    int num = 0;
    int row = 25;
    int col = 100;
    Color bg = new Color(255, 255, 200);
    Color fg = new Color(0, 0, 255);
JPanel p = new JPanel(null);
p.setPreferredSize(new Dimension(1200,5000));
    for (int r = 0; r < row * 100; r+=row)
    {
      for (int c = 0; c < col * 12; c+=col)
      {
        txa[num] = new JTextArea();
//scr.add(txa[num]);
p.add(txa[num]);
        txa[num].setBounds(c, r, col, row);
        txa[num].setBorder(BorderFactory.createLineBorder(Color.black));
        txa[num].setBackground(bg);
        txa[num].setForeground(fg);
        num++;
      }
    }
scr.setViewportView(p);
    add(scr);
//scr.setVisible(true);
  }

  public static void main(String[] args)
  {
    Form f = new Form();
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
//f.setSize(1200, 5000);
f.pack();
    f.setTitle("Form");
    f.setResizable(false);
    f.setLocation(0, 0);
    f.setVisible(true);
  }

  public void actionPerformed(ActionEvent e)
  {
  }
}

[Ted Newholm]

Thanks Michael. That worked well.

Much appreciated.

BTW. Does JPanel p = new JPanel(null) set the Layout to null the same as p.setLayout(null)?

[Maneesh Godbole]

Using a null layout is always a bad idea because then you need to worry about the user resizing the frame or running on a different screen resolution/size.
Always use a proper layout manager. With that, all you need to do is wrap your widget inside a JScrollPane and add the scroll pane to the parent panel.

[Michael Dunn]

> BTW. Does JPanel p = new JPanel(null) set the Layout to null the same as p.setLayout(null)?

yes, this is one of the constructors from JPanel's apidocs

JPanel
public JPanel(LayoutManager layout)Create a new buffered JPanel with the specified layout manager

Parameters:
layout - the LayoutManager to use

to follow up on Maneesh's comment re null layouts, the reason there was no scrollbar would be due to
you setting the scrollpane's layout to null (a null layout makes you responsible for just about everything).
The JScrollBar is a separate component, but when added to a null layout it needs to have a location and a size,
otherwise defaults to 0,0,0,0.

[Ted Newholm]

Thanks for your comments guys.

The reason I didn't use a Layout Manager was because I wanted the user to be able to resize the individual text areas. I also wanted to write some code so that columns and rows of text areas could also be moved - similar to a spreadsheet.
A GridLayout would work very nicely except column and row movement would be impossible - I think.

I've been putting off working with that GridBag thingy, it looks a bit intimidating and I'm not sure it would allow me to do what I want to do anyway.

[Ted Newholm]

I took your advice and have been looking at the Grouped Layout Manager. The following code creates a 2 x 2 group of buttons, c0, c1, c2 and c3.

Everything works fine if the buttons are coded individually. However, if I try using a button array (btn[4]) and enter them via a for loop I get a runtime error.

Exception in thread "main" java.lang.IllegalArgumentException: Component must be
non-null
at javax.swing.GroupLayout$ComponentSpring.<init>(GroupLayout.java:2953)
at javax.swing.GroupLayout$ComponentSpring.<init>(GroupLayout.java:2933)
at javax.swing.GroupLayout$Group.addComponent(GroupLayout.java:1524)
at javax.swing.GroupLayout$ParallelGroup.addComponent(GroupLayout.java:2484)
at javax.swing.GroupLayout$ParallelGroup.addComponent(GroupLayout.java:2454)
at javax.swing.GroupLayout$Group.addComponent(GroupLayout.java:1505)
at javax.swing.GroupLayout$ParallelGroup.addComponent(GroupLayout.java:2476)
at GroupedLayout2x2.<init>(GroupedLayout2x2.java:32)
at GroupedLayout2x2.main(GroupedLayout2x2.java:61)

The code is as follows:

import java.io.*;
import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;
import java.text.*;
import java.util.*;
import java.lang.*;

public class GroupedLayout2x2 extends Frame
{
	JPanel panel = new JPanel();
/*	JButton c0 = new JButton("c0");
	JButton c1 = new JButton("c1");
	JButton c2 = new JButton("c2");
	JButton c3 = new JButton("c3");
*/
	JButton[] btn = new JButton[4];

	public GroupedLayout2x2()
	{
		GroupLayout layout = new GroupLayout(panel);
		panel.setLayout(layout);

		layout.setAutoCreateGaps(true);
		layout.setAutoCreateContainerGaps(true);

		int n = 0;
		for (int i = 0; i < 2; i++)
		{
			btn[i] = new JButton();
			layout.setHorizontalGroup(
				layout.createSequentialGroup()
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i]))
	//					.addComponent(c0)
	//					.addComponent(c1))
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i+2])));
	//					.addComponent(c2)
	//					.addComponent(c3)));

			layout.setVerticalGroup(
				layout.createSequentialGroup()
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i+n]))
	//					 .addComponent(c0)
	//					 .addComponent(c2))
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i+n+1])));
	//					 .addComponent(c1)
	//					 .addComponent(c3)));
			n+=1;
		}
		this.add(panel);
		panel.setBackground(Color.black);
	}

	public static void main(String[] args)
	{
		GroupedLayout2x2 g = new GroupedLayout2x2();
		g.pack();
		g.setTitle("Group Layout");
		g.setVisible(true);
	}
}

Appreciate any help.

[Paul Clapham]

Well, yeah. You're not initializing all of the array entries, you're leaving nulls in some of them. And then you pass those nulls to the layout, which rightly complains about that.

[Ted Newholm]

Paul,
Thanks for reply. I've fixed up the initializing problem but I'm still getting a whole pile of runtime errors.

I now have the following loops:

		for (int i = 0; i < 2; i++)
		{
			btn[i] = new JButton();
			btn[i+2] = new JButton();

			layout.setHorizontalGroup(
				layout.createSequentialGroup()
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i]))
	//					.addComponent(c0)
	//					.addComponent(c1))
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i+2])));
	//					.addComponent(c2)
	//					.addComponent(c3)));
		}
		
		int n = 0;
		for (int i = 0; i < 2; i++)
		{
			layout.setVerticalGroup(
				layout.createSequentialGroup()
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i+n]))
	//					 .addComponent(c0)
	//					 .addComponent(c2))
					.addGroup(layout.createParallelGroup()
						.addComponent(btn[i+n+1])));
	//					 .addComponent(c1)
	//					 .addComponent(c3)));
			n+=1;
		}

Am I doing something wrong with the GroupLayout?

[Paul Clapham]

Ted Newholm wrote:I've fixed up the initializing problem but I'm still getting a whole pile of runtime errors... Am I doing something wrong with the GroupLayout?

If you're getting runtime errors, then yes, by definition you're doing something wrong. And the error messages are supposed to convey information, you know. I suggest you have a look at them and find out what that information is. That's what I would do. Without that information you're basically guessing in the dark.