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Dynamic button creation in Java

I am trying to dynamically generate a form. Basically, I want to upload a list of items to buy and create a button for each. I can confirm that the buttons are generated using the debugger, but they are not displayed. This is in a subclass of JPanel :

 private void generate() { JButton b = new JButton("height test"); int btnHeight = b.getPreferredSize().height; int pnlHeight = this.getPreferredSize().height; int numButtons = pnlHeight / btnHeight; setLayout(new GridLayout(numButtons, 1)); Iterator<Drink> it = DrinkMenu.iterator(); for (int i = 0; i <= numButtons; ++i) { if (!it.hasNext()) { break; } final Drink dr = it.next(); b = new DrinkButton(dr); b.addActionListener(new ActionListener() { public void actionPerformed(ActionEvent e) { order.addDrink(dr); }}); add(b); } revalidate(); }

DrinkButton is a subclass of JButton . Any ideas?

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It works on my computer ...

 public class Panel extends JPanel { public Panel() { setLayout(new java.awt.GridLayout(4, 4)); for (int i = 0; i < 16; ++i) { JButton b = new JButton(String.valueOf(i)); b.addActionListener(new java.awt.event.ActionListener() { public void actionPerformed(java.awt.event.ActionEvent e) { //... } }); add(b); } } public static void main(String[] args) { SwingUtilities.invokeLater(new Runnable(){ @Override public void run(){ JFrame frame = new JFrame(); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setSize(new Dimension(300, 300)); frame.add(new Panel()); frame.setVisible(true); } }); } }

As far as I remember, your version also worked, although I had to delete your “drinking” code. Start with this example (it shows a good grid of 4x4 buttons) and determine what is wrong with your code.

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You can use revalidate() as shown in this example .

Appendix: Here my variation on @mKorbel is interesting answer , which shows a similar result for GridLayout . It looks like repaint() might be needed after revalidate() .

 import java.awt.*; import java.awt.event.*; import javax.swing.*; /** @see https://stackoverflow.com/questions/6395105 */ public class ValidateRevalidateRepaint { private JPanel center; private boolean validate = false; private boolean revalidate = true; private boolean repaint = true; public ValidateRevalidateRepaint() { center = new JPanel(new GridLayout(1, 0, 10, 10)); JFrame f = new JFrame(); f.setTitle("VRR"); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.add(center, BorderLayout.CENTER); f.add(getRadioPanel(), BorderLayout.EAST); f.add(getCheckBoxPanel(), BorderLayout.SOUTH); makeChange(4); f.pack(); f.setLocationRelativeTo(null); f.setVisible(true); } private JPanel getRadioPanel() { JPanel panel = new JPanel(new GridLayout(0, 1)); ButtonGroup group = new ButtonGroup(); ActionListener l = new ActionListener() { @Override public void actionPerformed(ActionEvent e) { JRadioButton radio = (JRadioButton) e.getSource(); int n = Integer.parseInt(radio.getActionCommand()); makeChange(n); } }; for (int j = 0; j < 4; j++) { String s = String.valueOf(j + 1); JRadioButton radio = new JRadioButton(s); radio.setActionCommand(s); radio.addActionListener(l); group.add(radio); panel.add(radio); if (j == 3) { group.setSelected(radio.getModel(), true); } } return panel; } private JPanel getCheckBoxPanel() { final String[] operations = {"validate", "revalidate", "repaint"}; ActionListener l = new ActionListener() { @Override public void actionPerformed(ActionEvent e) { JCheckBox checkBox = (JCheckBox) e.getSource(); String ac = checkBox.getActionCommand(); boolean state = checkBox.isSelected(); if (ac.equals("validate")) { validate = state; } if (ac.equals("revalidate")) { revalidate = state; } if (ac.equals("repaint")) { repaint = state; } } }; JPanel panel = new JPanel(); for (int j = 0; j < operations.length; j++) { JCheckBox check = new JCheckBox(operations[j]); if (j == 0) { check.setSelected(false); } else { check.setSelected(true); } check.setActionCommand(operations[j]); check.addActionListener(l); panel.add(check); } return panel; } private void makeChange(int number) { center.removeAll(); for (int j = 0; j < number; j++) { center.add(getFiller()); } if (validate) { center.validate(); } if (revalidate) { center.revalidate(); } if (repaint) { center.repaint(); } } private JPanel getFiller() { JPanel panel = new JPanel(); panel.setBorder(BorderFactory.createLineBorder(Color.blue, 5)); panel.setBackground(Color.red); panel.setPreferredSize(new Dimension(50, 50)); return panel; } public static void main(String[] args) { EventQueue.invokeLater(new Runnable() { @Override public void run() { new ValidateRevalidateRepaint(); } }); } }
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example on validate () revalidate () plus repaint (), look as required for the correct output to the GUI created by some of LayourManagers

EDIT: as trashgod noted, I added a job schedule for EDT

  import java.awt.*; import java.awt.event.*; import javax.swing.*; public class ValidateRevalidateRepaint { private JPanel panel; private GridBagConstraints gbc; private boolean validate, revalidate, repaint; public ValidateRevalidateRepaint() { validate = revalidate = repaint = false; panel = new JPanel(new GridBagLayout()); gbc = new GridBagConstraints(); gbc.insets = new Insets(0, 20, 0, 20); panel.add(getFiller(), gbc); JFrame f = new JFrame(); f.setJMenuBar(getMenuBar()); f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); f.getContentPane().add(panel); f.getContentPane().add(getRadioPanel(), "East"); f.getContentPane().add(getCheckBoxPanel(), "South"); f.setSize(400, 200); f.setLocation(200, 200); f.setVisible(true); } private JMenuBar getMenuBar() { JMenu menu = new JMenu("change"); ActionListener l = new ActionListener() { @Override public void actionPerformed(ActionEvent e) { JMenuItem item = (JMenuItem) e.getSource(); int n = Integer.parseInt(item.getActionCommand()); makeChange(n); } }; for (int j = 1; j < 5; j++) { String s = String.valueOf(j) + " component"; if (j > 1) { s += "s"; } JMenuItem item = new JMenuItem(s); item.setActionCommand(String.valueOf(j)); item.addActionListener(l); menu.add(item); } JMenuBar menuBar = new JMenuBar(); menuBar.add(menu); return menuBar; } private JPanel getRadioPanel() { JPanel panel1 = new JPanel(new GridBagLayout()); GridBagConstraints gbc1 = new GridBagConstraints(); gbc1.insets = new Insets(2, 2, 2, 2); gbc1.weighty = 1.0; gbc1.gridwidth = GridBagConstraints.REMAINDER; ButtonGroup group = new ButtonGroup(); ActionListener l = new ActionListener() { @Override public void actionPerformed(ActionEvent e) { JRadioButton radio = (JRadioButton) e.getSource(); int n = Integer.parseInt(radio.getActionCommand()); makeChange(n); } }; for (int j = 0; j < 4; j++) { String s = String.valueOf(j + 1); JRadioButton radio = new JRadioButton(s); radio.setActionCommand(s); radio.addActionListener(l); group.add(radio); panel1.add(radio, gbc1); } return panel1; } private JPanel getCheckBoxPanel() { final String[] operations = {"validate", "revalidate", "repaint"}; ActionListener l = new ActionListener() { @Override public void actionPerformed(ActionEvent e) { JCheckBox checkBox = (JCheckBox) e.getSource(); String ac = checkBox.getActionCommand(); boolean state = checkBox.isSelected(); if (ac.equals("validate")) { validate = state; } if (ac.equals("revalidate")) { revalidate = state; } if (ac.equals("repaint")) { repaint = state; } } }; JPanel panel2 = new JPanel(); for (int j = 0; j < operations.length; j++) { JCheckBox check = new JCheckBox(operations[j]); check.setActionCommand(operations[j]); check.addActionListener(l); panel2.add(check); } return panel2; } private void makeChange(int number) { panel.removeAll(); for (int j = 0; j < number; j++) { panel.add(getFiller(), gbc); } if (validate) { panel.validate(); } if (revalidate) { panel.revalidate(); } if (repaint) { panel.repaint(); } } private JPanel getFiller() { JPanel panel3 = new JPanel(); panel3.setBackground(Color.red); panel3.setPreferredSize(new Dimension(40, 40)); return panel3; } public static void main(String[] args) {//added Schedule a job for the EDT javax.swing.SwingUtilities.invokeLater(new Runnable() { @Override public void run() { ValidateRevalidateRepaint rVR = new ValidateRevalidateRepaint(); } }); } }
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