CODEWITHSUNDEEP
java
b321234
b321234

Reputation: 17

JScrollPane won't work

Hey guys I wanted to create a JScrollPane but it won't work... and I don't know why... here's my code...

public class test extends JFrame{
    public test(){      
        setSize(1000,600);

    }

    private static JButton[] remove;
    private static JPanel p = new JPanel();

    public static void main(String[]args){
        p.setLayout(null);
        JFrame t=new test();
        remove = new JButton[25];
        for(int i=0;i<25;i++){
            remove[i]=new JButton("Remove");
            remove[i].setBounds(243,92+35*i,85,25);
            p.add(remove[i]);       
        }
        JScrollPane scrollPane = new JScrollPane(p);
        scrollPane.setVerticalScrollBarPolicy(JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED);
        t.add(scrollPane);
        t.setVisible(true);
    }

Umm and Im pretty sure the frame isn't big enough for these 25 buttons... But if i delete that p.setLayout(null); A horizontal scroll bar will be created automatically... I don't really know what is wrong with my code... Pls help thank you very much!

Upvotes: 0

Views: 2185

Answers (2)

Hovercraft Full Of Eels
Hovercraft Full Of Eels

Reputation: 285460

You need to set p's preferredSize for this to work.

  p.setPreferredSize(new Dimension(800, 2000));

Or you could have p extend JPanel and then override the getPreferredSize() method to return the proper dimension.

And I agree -- get rid of your null layouts. Learn about and use the layout managers if you want to use Swing correctly and have robust Swing GUI's.

e.g.,

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

public class Foo extends JFrame {

   private static final int BUTTON_COUNT = 25;

   public static void main(String[] args) {
      JPanel btnPanel = new JPanel(new GridLayout(0, 1, 0, 20));
      btnPanel.setBorder(BorderFactory.createEmptyBorder(20, 20, 20, 20));
      AbstractAction removeAction = new AbstractAction("Remove") {

         @Override
         public void actionPerformed(ActionEvent evt) {
            JButton src = (JButton) evt.getSource();
            JPanel container = (JPanel) src.getParent();
            container.remove(src);
            container.revalidate();
            container.repaint();
         }
      };
      for (int i = 0; i < BUTTON_COUNT; i++) {
         JButton removeBtn = new JButton(removeAction);
         btnPanel.add(removeBtn);
      }
      JPanel borderPanel = new JPanel(new BorderLayout());
      borderPanel.add(btnPanel, BorderLayout.NORTH);
      JScrollPane scrollpane = new JScrollPane(borderPanel,
            JScrollPane.VERTICAL_SCROLLBAR_ALWAYS,
            JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
      scrollpane.setPreferredSize(new Dimension(400, 800));

      JFrame frame = new JFrame("Foo");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(scrollpane);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

}

Upvotes: 3

Chad Campbell
Chad Campbell

Reputation: 321

The issue is that a scroll pane checks the component inside it for a "preferred size" so a pane with a null layout has a preferred size of (0,0). Which it ignores.

You should do something along the lines of:

p.setPreferredSize(1000,600);

And you should see some scroll bars appear, I'm not sure how accurate they will be though.

Upvotes: 0

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