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

java.lang.Object
  extended by com.google.gwt.user.client.ui.UIObject
      extended by com.google.gwt.user.client.ui.Widget
          extended by com.google.gwt.user.client.ui.Composite
All Implemented Interfaces:
EventListener
Direct Known Subclasses:
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
      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);
  }
}


Constructor Summary
Composite()
           
 
Method Summary
 Element getElement()
          This override checks to ensure initWidget(Widget) has been called.
protected  void initWidget(Widget widget)
          Sets the widget to be wrapped by the composite.
protected  void onAttach()
          This method is called when a widget is attached to the browser's document.
protected  void onDetach()
          This method is called when a widget is detached from the browser's document.
protected  void setWidget(Widget widget)
          Deprecated. this method is deprecated, and will be removed when GWT leaves beta (use initWidget(Widget) instead)
 
Methods inherited from class com.google.gwt.user.client.ui.Widget
getParent, isAttached, onBrowserEvent, onLoad, removeFromParent
 
Methods inherited from class com.google.gwt.user.client.ui.UIObject
addStyleName, getAbsoluteLeft, getAbsoluteTop, getOffsetHeight, getOffsetWidth, getStyleName, getTitle, isVisible, isVisible, removeStyleName, setElement, setHeight, setPixelSize, setSize, setStyleName, setStyleName, setTitle, setVisible, setVisible, setWidth, sinkEvents, toString, unsinkEvents
 
Methods inherited from class java.lang.Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait
 

Constructor Detail

Composite

public Composite()
Method Detail

getElement

public Element getElement()
This override checks to ensure initWidget(Widget) has been called.

Overrides:
getElement in class UIObject
Returns:
the object's browser element

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. It must not be overridden, except by Panel. To receive notification when a widget is attached to the document, override the Widget.onLoad() method.

Overrides:
onAttach in class Widget

onDetach

protected void onDetach()
Description copied from class: Widget
This method is called when a widget is detached from the browser's document. It must not be overridden, except by Panel.

Overrides:
onDetach in class Widget

setWidget

protected void setWidget(Widget widget)
Deprecated. this method is deprecated, and will be removed when GWT leaves beta (use initWidget(Widget) instead)

Sets the widget to be wrapped by the composite.

Parameters:
widget - the widget to be wrapped