How to get a combo box to show on button click in java?

Question

i am trying to get it so when a button is pressed a combo box is displayed in java. here is what i have tried.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Font;
import java.awt.event.*;
import javax.swing.*; 
import javax.swing.border.TitledBorder;
public class main {
    public static void main(String[] args) { 
        final JFrame testFrame = new JFrame();
        testFrame.setSize(300,450);     
        testFrame.setLocation(150,250);     
        testFrame.setTitle("My frame");
        testFrame.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
        testFrame.setResizable(true);       
        testFrame.setVisible(true); 
        testFrame.setLayout(new FlowLayout());
        final JButton testButton = new JButton("show");
        testFrame.add(testButton);


        class MyListener implements ActionListener 
         {
            public void actionPerformed(ActionEvent event) {
                JButton clickedButton = (JButton) event.getSource();
                if (clickedButton == testButton) {
                    String[] myArray = {"test","test2"};
                    JComboBox testingCom = new JComboBox(myArray);
                    testFrame.add(testingCom);
                }
            }
         }



    }

}

Any help would be much appreciated. thank you.

Answer 1

Based in your code, you never addActionListener to your button. In your ActionListener , you are creating a new instance of a combobox each time actionPerformed is called, and i don't if it's that what you want, you may be interested in if it's visible or not.

So you can change your code like this:

      final JButton testButton = new JButton("show");
      final JComboBox combo = new JComboBox(new String[]{"test1","test2"});
      testButton.addActionListener(new ActionListener(){
              // this is anonymous class
             @Override
             public void actionPerformed(ActionEvent evt){
                  //then you know that is attached to this button
                  combo.setVisible(!combo.isVisible());
             }
      });              
      combo.setVisible(Boolean.FALSE);
      testFrame.add(testButton);
      testFrame.add(combo);

Answer 2

Simply set the combo visible or invisible in the ActionListener and then revalidate and repaint its container. eg,

import java.awt.Dimension;
import java.awt.event.ActionEvent;
import javax.swing.AbstractAction;
import javax.swing.JButton;
import javax.swing.JComboBox;
import javax.swing.JOptionPane;
import javax.swing.JPanel;

public class Main {
   public static void main(String[] args) {
      final JComboBox<String> myCombo = new JComboBox<String>(new String[]{"Foo", "Bar"});
      final JPanel mainPanel = new JPanel();
      mainPanel.setPreferredSize(new Dimension(250, 100));
      mainPanel.add(new JButton(new AbstractAction("Toggle Combo") {

         @Override
         public void actionPerformed(ActionEvent arg0) {
            myCombo.setVisible(!myCombo.isVisible());
            mainPanel.revalidate();
            mainPanel.repaint();
         }
      }));
      mainPanel.add(myCombo);

      JOptionPane.showMessageDialog(null, mainPanel);
   }

}

Perhaps a cleaner way to do it is to use a CardLayout. If you use this, your components won't be shifting on removal and reviewing of the combo. For example:

import java.awt.CardLayout;
import java.awt.event.ActionEvent;

import javax.swing.*;

public class Main2 {
   public static void main(String[] args) {
      final JComboBox<String> myCombo = new JComboBox<String>(new String[]{"Foo", "Bar"});

      final CardLayout cardLayout = new CardLayout();
      final JPanel cardPanel = new JPanel(cardLayout);
      cardPanel.add(myCombo, "combo");
      cardPanel.add(new JLabel(), "empty");

      final JPanel mainPanel = new JPanel();
      mainPanel.add(new JButton(new AbstractAction("Toggle Combo") {

         @Override
         public void actionPerformed(ActionEvent evt) {
            cardLayout.next(cardPanel);
         }
      }));
      mainPanel.add(cardPanel);

      JOptionPane.showMessageDialog(null, mainPanel);
   }

}