The JFC Swing Tutorial: A Guide to Constructing GUIs (2nd Edition)

Container events are fired by a Container just after a component is added to or removed from the container. These events are for notification onlyno container listener need be present for components to be successfully added or removed.

Figure 3 demonstrates container events. By clicking Add a button or Remove a button , you can add buttons to or remove them from a panel at the bottom of the window. Each time a button is added to or removed from the panel, the panel fires a container event, and the panel's container listener is notified. The listener displays descriptive messages in the text area at the top of the window.

Try This:

1. Run ContainerEventDemo using Java Web Start or compile and run the example yourself. [6] [6] To run ContainerEventDemo using Java Web Start, click the ContainerEventDemo link on the RunExamples/events.html page on the CD. You can find the source files here: JavaTutorial/uiswing/events/example-1dot4/index.html#ContainerEventDemo .

2. Click the button labeled Add a button . You'll see a button appear near the bottom of the window. The container listener reacts to the resulting component-added event by displaying " JButton #1 was added to javax.swing.JPanel " at the top of the window.

3. Click the button labeled Remove a button . This removes the most recently added button from the panel, causing the container listener to receive a component-removed event.

You can find the demo's code in ContainerEventDemo.java . Here's the demo's container event-handling code:

public class ContainerEventDemo ... implements ContainerListener ... { ...//where initialization occurs: buttonPanel = new JPanel(new GridLayout(1,1)); buttonPanel.addContainerListener(this); ... public void componentAdded(ContainerEvent e) { displayMessage(" added to ", e); } public void componentRemoved(ContainerEvent e) { displayMessage(" removed from ", e); } void displayMessage(String action, ContainerEvent e) { display.append(((JButton)e.getChild()).getText() + " was" + action + e.getContainer().getClass().getName() + newline); } ... }

The Container Listener API

Table 9 lists the methods in the ContainerListener interface and Table 10 describes the methods in the ContainerEvent class. Also refer to the API documentation for ContainerListener at: http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/ContainerListener.html. The API documentation for ContainerEvent is online at: http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/ContainerEvent.html.

Table 9. The ContainerListener Interface (The corresponding adapter class is ContainerAdapter . ^[a] )

^[a] ContainerAdapter API documentation: http://java.sun.com/j2se/1.4.2/docs/api/java/awt/event/ContainerAdapter.html.

Table 10. The ContainerEvent Class

Examples That Use Container Listeners

The following examples use container listeners.