ComboBox ItemListener calling twice..

[Vijay Vaddem]

Hi,

Whenever a item is selected from JComboBox, the itemListener
method is called twice..... !!???

Why is it happening, i need this method to be called only once with
the current selected item. But its calling this method with both, current
and previous selected item...

here is the code...

 public class TestComboBox implements ItemListener
{
 
    JPanel cards; //a panel that uses CardLayout
    final static String BUTTONPANEL = "JPanel with JButtons";
    final static String TEXTPANEL = "JPanel with JTextField";
    JPanel card1, card2;
    
    public static void main(String[] args) {
        //Schedule a job for the event-dispatching thread:
        //creating and showing this application's GUI.
        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                createAndShowGUI();
            }
        });
    }
    
    private static void createAndShowGUI() {
        //Make sure we have nice window decorations.
        JFrame.setDefaultLookAndFeelDecorated(true);
 
        //Create and set up the window.
        JFrame frame = new JFrame("CardLayoutDemo");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
 
        //Create and set up the content pane.
        TestComboBox demo = new TestComboBox();
        demo.addComponentToPane(frame.getContentPane());
 
        //Display the window.
        frame.pack();
        frame.setVisible(true);
    }
 
    public void addComponentToPane(Container pane) {
        //Put the JComboBox in a JPanel to get a nicer look.
        JPanel comboBoxPane = new JPanel(); //use FlowLayout
        String comboBoxItems[] = { BUTTONPANEL, TEXTPANEL };
        JComboBox cb = new JComboBox(comboBoxItems);
        cb.setEditable(false);
        cb.addItemListener(this);
        comboBoxPane.add(cb);
 
        //Create the "cards".
        card1 = new JPanel();
        card1.add(new JButton("Button 1"));
        card1.add(new JButton("Button 2"));
 
        card2 = new JPanel();
        card2.add(new JTextField("TextField", 20));
        
        //Create the panel that contains the "cards".
        cards = new JPanel(new CardLayout());
        cards.add(card1, BUTTONPANEL);
        cards.add(card2, TEXTPANEL);
 
        pane.add(comboBoxPane, BorderLayout.PAGE_START);
        pane.add(cards, BorderLayout.CENTER);
    }
 
    public void itemStateChanged(ItemEvent evt) {
        CardLayout cl = (CardLayout)(cards.getLayout());
        cl.show(cards, (String)evt.getItem());
        String item = (String) evt.getItem();
        System.out.println("ITEM:"+item);
    }
 
}
 

[sasi kala]

Hi vijay,

The behavior of ItemListener is like that only.
It will call itemStateChanged two times because,
one of the item lost focus,
another one gains focus.
so it will call two times.

My suggestion is use ActionListener , and write actionPerformed like this

 
        JComboBox combo = (JComboBox) e.getSource();
        System.out.println(combo.getSelectedItem()+"");
 

Hope This Helps.
All The Best

[Michael Dunn]

<aircode>

public void itemStateChanged(ItemEvent evt)
{
  if(evt.getStateChange() == ItemEvent.SELECTED) 
  { 
    CardLayout cl = (CardLayout)(cards.getLayout());
    cl.show(cards, (String)evt.getItem());
    String item = (String) evt.getItem();
    System.out.println("ITEM:"+item);
  }
}

[Vijay Vaddem]

It worked!

Thanks.....

[Reyada Wolak]

sasi kala wrote:Hi vijay,

The behavior of ItemListener is like that only.
It will call itemStateChanged two times because,
one of the item lost focus,
another one gains focus.
so it will call two times.

My suggestion is use ActionListener , and write actionPerformed like this

 
        JComboBox combo = (JComboBox) e.getSource();
        System.out.println(combo.getSelectedItem()+"");
 

Hope This Helps.
All The Best

i tried to setFocusable(false) and it works just fine.

[Darryl Burke]

I think you missed the point, and also that this question was asked and resolved 5 years ago.

sasi kala's terminology was off. One item loses the selection, and the other gains it. Not focus.