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:

HasHandlers, EventListener

Direct Known Subclasses:

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

public class Widget
extends UIObject
implements EventListener, HasHandlers

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.

Widget

public Widget()

fireEvent

public void fireEvent(GwtEvent<?> event)

Description copied from interface: HasHandlers

Fires the given event to all the appropriate handlers.

Specified by:

fireEvent in interface HasHandlers

Parameters:

event - the event to be fired

getLayoutData

public java.lang.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).

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:

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

setLayoutData

public void setLayoutData(java.lang.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

addDomHandler

protected 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

protected 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

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.

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:

java.lang.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.

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:

java.lang.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.