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:

HasAttachHandlers, HasHandlers, EventListener, HasVisibility, IsWidget

Direct Known Subclasses:

AbstractNativeScrollbar, CellWidget, Composite, FocusWidget, Frame, Hidden, Hyperlink, Image, LabelBase, MenuBar, Panel, Tree

public class Widget
extends UIObject
implements EventListener, HasAttachHandlers, IsWidget

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.

Nested Class Summary

Nested classes/interfaces inherited from class com.google.gwt.user.client.ui.UIObject

UIObject.DebugIdImpl, UIObject.DebugIdImplEnabled

Field Summary

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

DEBUG_ID_PREFIX

Constructor Summary

Constructors

Constructor and Description
Widget()

Method Summary

Methods

Modifier and Type	Method and Description
HandlerRegistration	addAttachHandler(AttachEvent.Handler handler) Adds an AttachEvent handler.
<H extends EventHandler> HandlerRegistration	addBitlessDomHandler(H handler, DomEvent.Type<H> type) For browsers which do not leak, adds a native event handler to the widget.
<H extends EventHandler> HandlerRegistration	addDomHandler(H handler, DomEvent.Type<H> type) Adds a native event handler to the widget and sinks the corresponding native event.
<H extends EventHandler> HandlerRegistration	addHandler(H handler, GwtEvent.Type<H> type) Adds this handler to the widget.
Widget	asWidget() Returns the Widget aspect of the receiver.
static Widget	asWidgetOrNull(IsWidget w) This convenience method makes a null-safe call to IsWidget.asWidget().
protected HandlerManager	createHandlerManager() Creates the HandlerManager used by this Widget.
protected void	delegateEvent(Widget target, GwtEvent<?> event) Fires an event on a child widget.
protected void	doAttachChildren() If a widget contains one or more child widgets that are not in the logical widget hierarchy (the child is physically connected only on the DOM level), it must override this method and call onAttach() for each of its child widgets.
protected void	doDetachChildren() If a widget contains one or more child widgets that are not in the logical widget hierarchy (the child is physically connected only on the DOM level), it must override this method and call onDetach() for each of its child widgets.
void	fireEvent(GwtEvent<?> event) Fires the given event to the handlers listening to the event's type.
protected int	getHandlerCount(GwtEvent.Type<?> type) Gets the number of handlers listening to the event type.
Object	getLayoutData() Gets the panel-defined layout data associated with this widget.
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 boolean	isOrWasAttached() Has this widget ever been attached?
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, if one exists.
void	setLayoutData(Object layoutData) Sets the panel-defined layout data associated with this widget.
void	sinkEvents(int eventBitsToAdd) Overridden to defer the call to super.sinkEvents until the first time this widget is attached to the dom, as a performance enhancement.
void	unsinkEvents(int eventBitsToRemove) Removes a set of events from this object's event list.

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

addStyleDependentName, addStyleName, ensureDebugId, ensureDebugId, ensureDebugId, getAbsoluteLeft, getAbsoluteTop, getElement, getOffsetHeight, getOffsetWidth, getStyleElement, getStyleName, getStyleName, getStylePrimaryName, getStylePrimaryName, getTitle, isVisible, isVisible, onEnsureDebugId, removeStyleDependentName, removeStyleName, resolvePotentialElement, setElement, setElement, setHeight, setPixelSize, setSize, setStyleDependentName, setStyleName, setStyleName, setStyleName, setStyleName, setStylePrimaryName, setStylePrimaryName, setTitle, setVisible, setVisible, setWidth, sinkBitlessEvent, toString

Methods inherited from class java.lang.Object

equals, finalize, getClass, hashCode

Constructor Detail

Widget

public Widget()

Method Detail

asWidgetOrNull

public static Widget asWidgetOrNull(IsWidget w)

This convenience method makes a null-safe call to IsWidget.asWidget().

Returns:

the widget aspect, or null if w is null

addAttachHandler

public HandlerRegistration addAttachHandler(AttachEvent.Handler handler)

Description copied from interface: HasAttachHandlers

Adds an AttachEvent handler.

Specified by:

addAttachHandler in interface HasAttachHandlers

Parameters:

handler - the handler

Returns:

the handler registration

addBitlessDomHandler

public final <H extends EventHandler> HandlerRegistration addBitlessDomHandler(H handler,
                                                                DomEvent.Type<H> type)

For browsers which do not leak, adds a native event handler to the widget. Note that, unlike the addDomHandler(EventHandler, com.google.gwt.event.dom.client.DomEvent.Type) implementation, there is no need to attach the widget to the DOM in order to cause the event handlers to be attached.

Type Parameters:

H - the type of handler to add

Parameters:

type - the event key

handler - the handler

Returns:

HandlerRegistration used to remove the handler

addDomHandler

public final <H extends EventHandler> HandlerRegistration addDomHandler(H handler,
                                                         DomEvent.Type<H> type)

Adds a native event handler to the widget and sinks the corresponding native event. If you do not want to sink the native event, use the generic addHandler method instead.

Type Parameters:

H - the type of handler to add

Parameters:

type - the event key

handler - the handler

Returns:

HandlerRegistration used to remove the handler

addHandler

public final <H extends EventHandler> HandlerRegistration addHandler(H handler,
                                                      GwtEvent.Type<H> type)

Adds this handler to the widget.

Type Parameters:

H - the type of handler to add

Parameters:

type - the event type

handler - the handler

Returns:

HandlerRegistration used to remove the handler

asWidget

public Widget asWidget()

Description copied from interface: IsWidget

Returns the Widget aspect of the receiver.

Specified by:

asWidget in interface IsWidget

fireEvent

public void fireEvent(GwtEvent<?> event)

Description copied from interface: HasHandlers

Fires the given event to the handlers listening to the event's type.

Any exceptions thrown by handlers will be bundled into a UmbrellaException and then re-thrown after all handlers have completed. An exception thrown by a handler will not prevent other handlers from executing.

Specified by:

fireEvent in interface HasHandlers

Parameters:

event - the event

getLayoutData

public Object getLayoutData()

Gets the panel-defined layout data associated with this widget.

Returns:

the widget's layout data

See Also:

setLayoutData(java.lang.Object)

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).

Specified by:

isAttached in interface HasAttachHandlers

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 one exists.

If it has no parent, this method does nothing. If it is a "root" widget (meaning it's been added to the detach list via RootPanel.detachOnWindowClose(Widget)), it will be removed from the detached immediately. This makes it possible for Composites and Panels to adopt root widgets.

Throws:

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

setLayoutData

public void setLayoutData(Object layoutData)

Sets the panel-defined layout data associated with this widget. Only the panel that currently contains a widget should ever set this value. It serves as a place to store layout bookkeeping data associated with a widget.

Parameters:

layoutData - the widget's layout data

sinkEvents

public void sinkEvents(int eventBitsToAdd)

Overridden to defer the call to super.sinkEvents until the first time this widget is attached to the dom, as a performance enhancement. Subclasses wishing to customize sinkEvents can preserve this deferred sink behavior by putting their implementation behind a check of isOrWasAttached():

 @Override
 public void sinkEvents(int eventBitsToAdd) {
   if (isOrWasAttached()) {
     /* customized sink code goes here */
   } else {
     super.sinkEvents(eventBitsToAdd);
  }
} 

Overrides:

sinkEvents in class UIObject

Parameters:

eventBitsToAdd - a bitfield representing the set of events to be added to this element's event set

See Also:

Event

unsinkEvents

public void unsinkEvents(int eventBitsToRemove)

Description copied from class: UIObject

Removes a set of events from this object's event list.

Overrides:

unsinkEvents in class UIObject

Parameters:

eventBitsToRemove - a bitfield representing the set of events to be removed from this element's event set

See Also:

UIObject.sinkEvents(int), Event

createHandlerManager

protected HandlerManager createHandlerManager()

Creates the HandlerManager used by this Widget. You can override this method to create a custom HandlerManager.

Returns:

the HandlerManager you want to use

delegateEvent

protected void delegateEvent(Widget target,
                 GwtEvent<?> event)

Fires an event on a child widget. Used to delegate the handling of an event from one widget to another.

Parameters:

event - the event

target - fire the event on the given target

doAttachChildren

protected void doAttachChildren()

If a widget contains one or more child widgets that are not in the logical widget hierarchy (the child is physically connected only on the DOM level), it must override this method and call onAttach() for each of its child widgets.

See Also:

onAttach()

doDetachChildren

protected void doDetachChildren()

If a widget contains one or more child widgets that are not in the logical widget hierarchy (the child is physically connected only on the DOM level), it must override this method and call onDetach() for each of its child widgets.

See Also:

onDetach()

getHandlerCount

protected int getHandlerCount(GwtEvent.Type<?> type)

Gets the number of handlers listening to the event type.

Parameters:

type - the event type

Returns:

the number of registered handlers

isOrWasAttached

protected final boolean isOrWasAttached()

Has this widget ever been attached?

Returns:

true if this widget ever been attached to the DOM, false otherwise

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 or use addAttachHandler(com.google.gwt.event.logical.shared.AttachEvent.Handler).

It is strongly recommended that you override onLoad() or 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.

Throws:

IllegalStateException - if this widget is already attached

See Also:

onLoad(), doAttachChildren()

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 or use addAttachHandler(com.google.gwt.event.logical.shared.AttachEvent.Handler).

It is strongly recommended that you override onUnload() or 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.

Throws:

IllegalStateException - if this widget is already detached

See Also:

onUnload(), doDetachChildren()

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.