populate multiple combobox with same model but select diff

Question

Having problems with the ComboBox, I have populated multiple ComboBoxes with the same model, but when I run my program and select a value from one

Answer 1

Use just a ListModel to manage your data and create a ComboboxModel adapter that is based on the ListModel. This ComboboxModel will only add the selection capability. Remember that a ComboboxModel extends ListModel. So it is easy to adapt the interfaces.

The only tricky part is to handle the update events.

For example:

public class ListAdapterComboboxModel implements ComboBoxModel {

    private ListModel dataModel;
    private Object selectedObject;
    private DataModelListDataListenerAdapter listDataListenerAdapter;

    public ListAdapterComboboxModel(ListModel ListModel) {
        dataModel = ListModel;
        this.listDataListenerAdapter = new DataModelListDataListenerAdapter();
        dataModel.addListDataListener(listDataListenerAdapter);
    }

    public int getSize() {
        return dataModel.getSize();
    }

    public Object getElementAt(int index) {
        return dataModel.getElementAt(index);
    }

    public void addListDataListener(ListDataListener l) {
        listDataListenerAdapter.addListDataListener(l);
    }

    public void removeListDataListener(ListDataListener l) {
        listDataListenerAdapter.removeListDataListener(l);
    }

    public void setSelectedItem(Object anObject) {
        if ((selectedObject != null && !selectedObject.equals(anObject))
                || selectedObject == null && anObject != null) {
            selectedObject = anObject;
            ListDataEvent e = new ListDataEvent(this,
                    ListDataEvent.CONTENTS_CHANGED, -1, -1);
            listDataListenerAdapter.delegateListDataEvent(e);
        }
    }

    public Object getSelectedItem() {
        return selectedObject;
    }

    private class DataModelListDataListenerAdapter implements ListDataListener {

        protected EventListenerList listenerList = new EventListenerList();

        public void removeListDataListener(ListDataListener l) {
            listenerList.remove(ListDataListener.class, l);
        }

        public void addListDataListener(ListDataListener l) {
            listenerList.add(ListDataListener.class, l);

        }

        public void intervalAdded(ListDataEvent e) {
            delegateListDataEvent(e);
        }

        public void intervalRemoved(ListDataEvent e) {
            checkSelection(e);
            delegateListDataEvent(e);
        }

        public void contentsChanged(ListDataEvent e) {
            checkSelection(e);
            delegateListDataEvent(e);
        }

        private void checkSelection(ListDataEvent e) {
            Object selectedItem = getSelectedItem();
            ListModel listModel = (ListModel) e.getSource();
            int size = listModel.getSize();
            boolean selectedItemNoLongerExists = true;
            for (int i = 0; i < size; i++) {
                Object elementAt = listModel.getElementAt(i);
                if (elementAt != null && elementAt.equals(selectedItem)) {
                    selectedItemNoLongerExists = false;
                    break;
                }
            }
            if (selectedItemNoLongerExists) {
                ListAdapterComboboxModel.this.selectedObject = null;
            }
        }

        protected void delegateListDataEvent(ListDataEvent lde) {
            ListDataListener[] listeners = listenerList
                    .getListeners(ListDataListener.class);
            for (ListDataListener listDataListener : listeners) {
                listDataListener.contentsChanged(lde);
            }
        }

    }

}

And then just use it like this

public class ComboboxModelTest extends JFrame{

    public static void main(String[] args) {
        ComboboxModelTest comboboxModelTest = new ComboboxModelTest();
        comboboxModelTest.pack();
        comboboxModelTest.setVisible(true);
    }

    public ComboboxModelTest() {
        Container contentPane = getContentPane();
        contentPane.setLayout(new FlowLayout());

        DefaultListModel defaultListModel = new DefaultListModel();
        defaultListModel.addElement("Element 1");
        defaultListModel.addElement("Element 2");

        ComboBoxModel firstComboboxModel = new ListAdapterComboboxModel(defaultListModel);
        ComboBoxModel secondComboboxModel = new ListAdapterComboboxModel(defaultListModel);
        JComboBox jComboBox1 = new JComboBox(firstComboboxModel);
        JComboBox jComboBox2 = new JComboBox(secondComboboxModel);

        contentPane.add(jComboBox1);
        contentPane.add(jComboBox2);
    }
}

Then you only have to manage the data in one ListModel and you have distinct selection models.

Also take a look at The MVC pattern and SWING.