com.google.gwt.user.client.ui
Class Composite

java.lang.Object
  com.google.gwt.user.client.ui.UIObject
      com.google.gwt.user.client.ui.Widget
          com.google.gwt.user.client.ui.Composite

All Implemented Interfaces:

HasHandlers, EventListener

Direct Known Subclasses:

CalendarView, CaptionPanel, DateBox, DatePicker, DisclosurePanel, MonthSelector, ResizeComposite, SuggestBox, TabBar, TabPanel

public abstract class Composite
extends Widget

A type of widget that can wrap another widget, hiding the wrapped widget's methods. When added to a panel, a composite behaves exactly as if the widget it wraps had been added.

The composite is useful for creating a single widget out of an aggregate of multiple other widgets contained in a single panel.

Example

public class CompositeExample implements EntryPoint {

  /**
   * A composite of a TextBox and a CheckBox that optionally enables it.
   */
  private static class OptionalTextBox extends Composite implements
      ClickHandler {

    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.addClickHandler(this);

      // All composites must call initWidget() in their constructors.
      initWidget(panel);

      // Give the overall composite a style name.
      setStyleName("example-OptionalCheckBox");
    }

    public void onClick(ClickEvent event) {
      if (event.getSource() == 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);
  }
}

Composite

public Composite()

isAttached

public boolean isAttached()

Description copied from class: Widget

Determines whether this widget is currently attached to the browser's document (i.e., there is an unbroken chain of widgets between this widget and the underlying browser document).

Overrides:

isAttached in class Widget

Returns:

true if the widget is attached

onBrowserEvent

public void onBrowserEvent(Event event)

Description copied from interface: EventListener

Fired whenever a browser event is received.

Specified by:

onBrowserEvent in interface EventListener

Overrides:

onBrowserEvent in class Widget

Parameters:

event - the event received

getWidget

protected Widget getWidget()

Provides subclasses access to the topmost widget that defines this composite.

Returns:

the widget

initWidget

protected void initWidget(Widget widget)

Sets the widget to be wrapped by the composite. The wrapped widget must be set before calling any Widget methods on this object, or adding it to a panel. This method may only be called once for a given composite.

Parameters:

widget - the widget to be wrapped

onAttach

protected void onAttach()

Description copied from class: Widget

This method is called when a widget is attached to the browser's document. To receive notification after a Widget has been added to the document, override the Widget.onLoad() method.

It is strongly recommended that you override Widget.onLoad() or Widget.doAttachChildren() instead of this method to avoid inconsistencies between logical and physical attachment states.

Subclasses that override this method must call super.onAttach() to ensure that the Widget has been attached to its underlying Element.

Overrides:

onAttach in class Widget

See Also:

Widget.onLoad(), Widget.doAttachChildren()

onDetach

protected void onDetach()

Description copied from class: Widget

This method is called when a widget is detached from the browser's document. To receive notification before a Widget is removed from the document, override the Widget.onUnload() method.

It is strongly recommended that you override Widget.onUnload() or Widget.doDetachChildren() instead of this method to avoid inconsistencies between logical and physical attachment states.

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 memory leaks due to circular references between DOM Elements and JavaScript objects.

Overrides:

onDetach in class Widget

See Also:

Widget.onUnload(), Widget.doDetachChildren()

setWidget

@Deprecated
protected void setWidget(Widget widget)

Deprecated. Use initWidget(Widget) instead

This method was for initializing the Widget to be wrapped by this Composite, but has been deprecated in favor of initWidget(Widget).