The composite is useful for creating a single widget out of an aggregate of multiple other widgets contained in a single panel.
public class CompositeExample implements EntryPoint { /** * A composite of a TextBox and a CheckBox that optionally enables it. */ private static class OptionalTextBox extends Composite implements ClickListener { private TextBox textBox = new TextBox(); private CheckBox checkBox = new CheckBox(); /** * Constructs an OptionalTextBox with the given caption on the check. * * @param caption the caption to be displayed with the check box */ public OptionalTextBox(String caption) { // Place the check above the text box using a vertical panel. VerticalPanel panel = new VerticalPanel(); panel.add(checkBox); panel.add(textBox); // Set the check box's caption, and check it by default. checkBox.setText(caption); checkBox.setChecked(true); checkBox.addClickListener(this); // All composites must call setWidget() in their constructors. initWidget(panel); // Give the overall composite a style name. setStyleName("example-OptionalCheckBox"); } public void onClick(Widget sender) { if (sender == checkBox) { // When the check box is clicked, update the text box's enabled state. textBox.setEnabled(checkBox.isChecked()); } } /** * Sets the caption associated with the check box. * * @param caption the check box's caption */ public void setCaption(String caption) { // Note how we use the use composition of the contained widgets to provide // only the methods that we want to. checkBox.setText(caption); } /** * Gets the caption associated with the check box. * * @return the check box's caption */ public String getCaption() { return checkBox.getText(); } } public void onModuleLoad() { // Create an optional text box and add it to the root panel. OptionalTextBox otb = new OptionalTextBox("Check this to enable me"); RootPanel.get().add(otb); } }
getElement() | This override checks to ensure initWidget(Widget) has been called. |
getWidget() | Provides subclasses access to the topmost widget that defines this composite. |
initWidget(Widget) | Sets the widget to be wrapped by the composite. |
onAttach() | This method is called when a widget is attached to the browser's document. |
onDetach() | This method is called when a widget is detached from the browser's document. |
setWidget(Widget) | Sets the widget to be wrapped by the composite. |
Subclasses that override this method must call
super.onAttach()
to ensure that the Widget has been
attached to the underlying Element.
Subclasses that override this method must call
super.onDetach()
to ensure that the Widget has been
detached from the underlying Element. Failure to do so will result
in application memeroy leaks due to circular references between DOM
Elements and JavaScript objects.