Widget (Google Web Toolkit Javadoc)

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, CellGridImpl.Cell, CellWidget, Composite, DataGrid.TableWidget, FileUpload, FocusWidget, Frame, Hidden, Hyperlink, Image, LabelBase, MenuBar, Panel, SplitLayoutPanel.Splitter, 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
Modifier and Type Field and Description

(package private) int eventsToSink
A bit-map of the events that should be sunk when the widget is attached to the DOM.
- Fields inherited from class com.google.gwt.user.client.ui.UIObject
  DEBUG_ID_PREFIX, MISSING_ELEMENT_ERROR, SETELEMENT_TWICE_ERROR

Fields
Modifier and Type	Field and Description
`(package private) int`	`eventsToSink` A bit-map of the events that should be sunk when the widget is attached to the DOM.

Constructor Summary

Constructors
Constructor and Description

Widget()

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.
`(package private) HandlerManager`	`ensureHandlers()` Ensures the existence of the handler manager.
`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.
`(package private) HandlerManager`	`getHandlerManager()`
`java.lang.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.
`(package private) void`	`replaceElement(Element elem)` Replaces this object's browser element.
`void`	`setLayoutData(java.lang.Object layoutData)` Sets the panel-defined layout data associated with this widget.
`(package private) void`	`setParent(Widget parent)` Sets this widget's parent.
`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
clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

- Field Detail
  - eventsToSink
```
int eventsToSink
```
    A bit-map of the events that should be sunk when the widget is attached to the DOM. (We delay the sinking of events to improve startup performance.) When the widget is attached, this is set to -1
    Package protected to allow Composite to see it.
- 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 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).
    
    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:
    
    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
  - 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:
    
    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 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:
    
    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.
  - ensureHandlers
```
HandlerManager ensureHandlers()
```
    Ensures the existence of the handler manager.
    
    Returns:
    the handler manager
  - getHandlerManager
```
HandlerManager getHandlerManager()
```
  - replaceElement
```
void replaceElement(Element elem)
```
    Description copied from class: UIObject
    
    Replaces this object's browser element. This method exists only to support a specific use-case in Image, and should not be used by other classes.
    
    Overrides:
    
    replaceElement in class UIObject
    
    Parameters:
    elem - the object's new element
  - setParent
```
void setParent(Widget parent)
```
    Sets this widget's parent. This method should only be called by Panel and Composite.
    
    Parameters:
    parent - the widget's new parent
    
    Throws:
    
    java.lang.IllegalStateException - if parent is non-null and the widget already has a parent

Class Widget

Nested Class Summary

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

Field Summary

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

Constructor Summary

Method Summary

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

Methods inherited from class java.lang.Object

Field Detail

eventsToSink

Constructor Detail

Widget

Method Detail

asWidgetOrNull

addAttachHandler

addBitlessDomHandler

addDomHandler

addHandler

asWidget

fireEvent

getLayoutData

getParent

isAttached

onBrowserEvent

removeFromParent

setLayoutData

sinkEvents

unsinkEvents

createHandlerManager

delegateEvent

doAttachChildren

doDetachChildren

getHandlerCount

isOrWasAttached

onAttach

onDetach

onLoad

onUnload

ensureHandlers

getHandlerManager

replaceElement

setParent