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

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

All Implemented Interfaces:

EventListener

Direct Known Subclasses:

Composite, FileUpload, FocusWidget, Frame, Hidden, Hyperlink, Image, Label, MenuBar, Panel, Tree

public class Widget
extends UIObject
implements EventListener

The base class for the majority of user-interface objects. Widget adds support for receiving events from the browser and being added directly to panels.

Constructor Summary

Widget()

Method Summary

protected void	doAttachChildren() If a widget implements HasWidgets, it must override this method and call onAttach() for each of its child widgets.
protected void	doDetachChildren() If a widget implements HasWidgets, it must override this method and call onDetach() for each of its child widgets.
Widget	getParent() Gets this widget's parent panel.
boolean	isAttached() 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).
protected void	onAttach() This method is called when a widget is attached to the browser's document.
void	onBrowserEvent(Event event) Fired whenever a browser event is received.
protected void	onDetach() This method is called when a widget is detached from the browser's document.
protected void	onLoad() This method is called immediately after a widget becomes attached to the browser's document.
protected void	onUnload() This method is called immediately before a widget will be detached from the browser's document.
void	removeFromParent() Removes this widget from its parent widget.
protected void	setElement(Element elem) Sets this object's browser element.

Methods inherited from class com.google.gwt.user.client.ui.UIObject

addStyleDependentName, addStyleName, getAbsoluteLeft, getAbsoluteTop, getElement, getOffsetHeight, getOffsetWidth, getStyleElement, getStyleName, getStyleName, getStylePrimaryName, getStylePrimaryName, getTitle, isVisible, isVisible, removeStyleDependentName, removeStyleName, setHeight, setPixelSize, setSize, setStyleName, setStyleName, setStyleName, setStylePrimaryName, setStylePrimaryName, 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

Widget

public Widget()

Method Detail

getParent

public Widget getParent()

Gets this widget's parent panel.

Returns:

the widget's parent panel

isAttached

public boolean isAttached()

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).

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

Parameters:

event - the event received

removeFromParent

public void removeFromParent()

Removes this widget from its parent widget. If it has no parent, this method does nothing.

Throws:

java.lang.IllegalStateException - if this widget's parent does not support removal (e.g. Composite)

doAttachChildren

protected void doAttachChildren()

If a widget implements HasWidgets, it must override this method and call onAttach() for each of its child widgets.

See Also:

onAttach()

doDetachChildren

protected void doDetachChildren()

If a widget implements HasWidgets, it must override this method and call onDetach() for each of its child widgets.

See Also:

onDetach()

onAttach

protected void onAttach()

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 onLoad() method.

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

Throws:

java.lang.IllegalStateException - if this widget is already attached

onDetach

protected void onDetach()

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 onUnload() method.

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.

Throws:

java.lang.IllegalStateException - if this widget is already detached

onLoad

protected void onLoad()

This method is called immediately after a widget becomes attached to the browser's document.

onUnload

protected void onUnload()

This method is called immediately before a widget will be detached from the browser's document.

setElement

protected void setElement(Element elem)

Sets this object's browser element. Widget subclasses must call this method before attempting to call any other methods. If a browser element has already been attached, then it is replaced with the new element. The old event listeners are removed from the old browser element, and the event listeners are set up on the new browser element.

Overrides:

setElement in class UIObject

Parameters:

elem - the object's new element