Multi tool use

Adding new comboboxes Java

I have a problem with Swing interface on java. Explaination: I have a Combobox with 1, 2, 3, 4, 5 items. When an exact item is selected I need to create some more comboboxes the number of which depends on the selected item. So, if number 5 is selected, 5 more comboboxes must appear in the frame. I used ActionListener but it did not work properly. However, the same code but outside Actionlistener works well. What a problem can it be?

public class FrameClass extends JFrame {
JPanel panel;
JComboBox box;

String s = {"1", "2", "3", "4", "5"};
String s1 = {"0", "1", "2", "3", "4", "5"};
public FrameClass() {
panel = new JPanel();
box = new JComboBox(s);
JComboBox adults = new JComboBox(s);
JComboBox children = new JComboBox(s1);

panel.add(box, BorderLayout.CENTER);

box.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
for(int i = 0; i <= box.getSelectedIndex(); i++) {
panel.add(adults, BorderLayout.WEST);
panel.add(children, BorderLayout.WEST);
}
}
});
add(panel);
}
}

public class MainClass {
public static void main(String args) {
JFrame frame = new FrameClass();
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.setExtendedState(Frame.MAXIMIZED_BOTH);
frame.getContentPane().setBackground(Color.WHITE);
frame.setVisible(true);
}
}


panel.revalidate();

1 Answer
1

The problem that you don't inform the layout manager about new elements in your panel.

Here is the correct variant of your action listener:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JComboBox;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.WindowConstants;

public class FrameClass extends JFrame {
JPanel panel;

JComboBox<String> box;

String s = {"1", "2", "3", "4", "5"};

String s1 = {"0", "1", "2", "3", "4", "5"};

public FrameClass() {
panel = new JPanel();
box = new JComboBox(s);
JComboBox adults = new JComboBox[5];
JComboBox children = new JComboBox[5];
for (int i = 0; i < 5; i++) {
adults[i] = new JComboBox<>(s);
children[i] = new JComboBox<>(s1);
}

panel.add(box, BorderLayout.CENTER);
JPanel nested = new JPanel();
add(nested, BorderLayout.EAST);
box.addActionListener(new ActionListener() {
@Override
public void actionPerformed(ActionEvent e) {
nested.removeAll();
nested.setLayout(new GridLayout(box.getSelectedIndex() + 1, 2));
for (int i = 0; i <= box.getSelectedIndex(); i++) {
nested.add(adults[i]);
nested.add(children[i]);
}
getContentPane().revalidate();
getContentPane().repaint();
pack();
}
});
add(panel);
}

public static void main(String args) {
JFrame frame = new FrameClass();
frame.setDefaultCloseOperation(WindowConstants.EXIT_ON_CLOSE);
frame.pack();
frame.getContentPane().setBackground(Color.WHITE);
frame.setLocationRelativeTo(null); // center the window
frame.setVisible(true);
}
}


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