JComboBox Selection Change Listener?

问题:

I\'m trying to get an event to fire whenever a choice is made from a JComboBox.

The problem I\'m having is that there is no obvious addSelectionListener() method.

I\'ve tried to use actionPerformed() but it never fires.

Short of overriding the model for the JComboBox I\'m out of ideas.

How do I get notified of a selection change on a JComboBox?

Edit: I have to apologize it turns out I was using a misbehaving subclass of JComboBox, but I\'ll leave the question up since your answer is good. Commence the vote down. :)

回答1:

It should respond to ActionListeners, like this:

combo.addActionListener (new ActionListener () {
    public void actionPerformed(ActionEvent e) {
        doSomething();
    }
});

@John Calsbeek rightly points out that addItemListener() will work, too. You may get 2 ItemEvents, though, one for the deselection of the previously selected item, and another for the selection of the new item. Just don\'t use both event types!

回答2:

Code example of ItemListener implementation

class ItemChangeListener implements ItemListener{
    @Override
    public void itemStateChanged(ItemEvent event) {
       if (event.getStateChange() == ItemEvent.SELECTED) {
          Object item = event.getItem();
          // do something with object
       }
    }       
}

Now we will get only selected item.

Then just add listener to your JComboBox

addItemListener(new ItemChangeListener());

回答3:

I would try the itemStateChanged() method of the ItemListener interface if jodonnell\'s solution fails.

回答4:

Here is creating a ComboBox adding a listener for item selection change:

    JComboBox comboBox = new JComboBox();

    comboBox.setBounds(84, 45, 150, 20);
    contentPane.add(comboBox);

    JComboBox comboBox_1 = new JComboBox();
    comboBox_1.setBounds(84, 97, 150, 20);
    contentPane.add(comboBox_1);
    comboBox.addItemListener(new ItemListener() {
        public void itemStateChanged(ItemEvent arg0) {
            //Do Something
        }
    });
}

回答5:

You may try these

 int selectedIndex = myComboBox.getSelectedIndex();

-or-

Object selectedObject = myComboBox.getSelectedItem();

-or-

String selectedValue = myComboBox.getSelectedValue().toString();

回答6:

I was recently looking for this very same solution and managed to find a simple one without assigning specific variables for the last selected item and the new selected item. And this question, although very helpful, didn\'t provide the solution I needed. This solved my problem, I hope it solves yours and others. Thanks.

How do I get the previous or last item?