Package 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, CellGridImpl.Cell, CellWidget, Composite, DataGrid.TableWidget, 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.

  • Field Details

    • 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 Details

    • Widget

      public Widget()

  • Method Details

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:

    • 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:
      IllegalStateException - if parent is non-null and the widget already has a parent