List Model Controls - The Definitive Guide to Java Swing - page 484

■ Note Besides setting the popupVisible property, you can use the public void hidePopup() and

public void showPopup() methods to toggle the pop-up list's visibility status.

Rendering JComboBox Elements
The rendering of elements within a JComboBox is done with a ListCellRenderer . This is the same
renderer that is used for a JList component. Once you've created a renderer for either one of
these two components, you can use that renderer for the other component. To reuse the
ComplexCellRenderer from earlier in the chapter (Listing 13-6), you could add the following
lines to the ComplexRenderingSample example (Listing 13-7) to have the two components share
the same renderer.

JComboBox comboBox = new JComboBox(elements);
comboBox.setRenderer(renderer);
frame.add(comboBox, BorderLayout.NORTH);

The result of adding these lines is shown in Figure 13-15.

Figure 13-15. A JComboBox with a custom renderer

Not all renderers will work as expected with both the JComboBox and JList components.
For instance, the FocusedTitleListCellRenderer demonstrated earlier in Figure 13-6 wouldn't
show the “Focused” title border in a JComboBox because the choices never had the input focus.
In addition, different components may have different default colors (a different unselected
background color, in this case). It may be necessary to ask what color the component normally
would be rendered in, and then act accordingly.

Selecting JComboBox Elements
The JComboBox component supports at least three different events related to selection.
You can listen for keyboard input to support key selection with the help of the JComboBox.
KeySelectionManager class. You can also listen with an ActionListener or an ItemListener
to find out when the selected item of the JComboBox changes.
If you want to programmatically select an element, use public void
setSelectedItem(Object element) or public void setSelectedIndex(int index) .