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

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

All Implemented Interfaces:

HasHandlers, EventListener, HasWidgets, java.lang.Iterable<Widget>

Direct Known Subclasses:

ComplexPanel, HorizontalSplitPanel, HTMLTable, SimplePanel, VerticalSplitPanel

public abstract class Panel
extends Widget
implements HasWidgets

Abstract base class for all panels, which are widgets that can contain other widgets.

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

Panel()

Method Summary

void	add(Widget child) Adds a child widget.
void	clear() Removes all child widgets.
abstract boolean	remove(Widget child) Removes a child widget.

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

fireEvent, getLayoutData, getParent, isAttached, onBrowserEvent, removeFromParent, setLayoutData, sinkEvents

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

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

Methods inherited from class java.lang.Object

equals, getClass, hashCode, notify, notifyAll, wait, wait, wait

Methods inherited from interface com.google.gwt.user.client.ui.HasWidgets

iterator

Constructor Detail

Panel

public Panel()

Method Detail

add

public void add(Widget child)

Adds a child widget.

How to Override this Method

There are several important things that must take place in the correct order to properly add or insert a Widget to a Panel. Not all of these steps will be relevant to every Panel, but all of the steps must be considered.

1. Validate: Perform any sanity checks to ensure the Panel can accept a new Widget. Examples: checking for a valid index on insertion; checking that the Panel is not full if there is a max capacity.
2. Adjust for Reinsertion: Some Panels need to handle the case where the Widget is already a child of this Panel. Example: when performing a reinsert, the index might need to be adjusted to account for the Widget's removal. See ComplexPanel.adjustIndex(Widget, int).
3. Detach Child: Remove the Widget from its existing parent, if any. Most Panels will simply call Widget.removeFromParent() on the Widget.
4. Logical Attach: Any state variables of the Panel should be updated to reflect the addition of the new Widget. Example: the Widget is added to the Panel's WidgetCollection at the appropriate index.
5. Physical Attach: The Widget's Element must be physically attached to the Panel's Element, either directly or indirectly.
6. Adopt: Call adopt(Widget) to finalize the add as the very last step.

Specified by:

add in interface HasWidgets

Parameters:

child - the widget to be added

Throws:

java.lang.UnsupportedOperationException - if this method is not supported (most often this means that a specific overload must be called)

See Also:

HasWidgets.add(Widget)

clear

public void clear()

Description copied from interface: HasWidgets

Removes all child widgets.

Specified by:

clear in interface HasWidgets

remove

public abstract boolean remove(Widget child)

Removes a child widget.

How to Override this Method

There are several important things that must take place in the correct order to properly remove a Widget from a Panel. Not all of these steps will be relevant to every Panel, but all of the steps must be considered.

1. Validate: Make sure this Panel is actually the parent of the child Widget; return false if it is not.
2. Orphan: Call orphan(Widget) first while the child Widget is still attached.
3. Physical Detach: Adjust the DOM to account for the removal of the child Widget. The Widget's Element must be physically removed from the DOM.
4. Logical Detach: Update the Panel's state variables to reflect the removal of the child Widget. Example: the Widget is removed from the Panel's WidgetCollection.

Specified by:

remove in interface HasWidgets

Parameters:

child - the widget to be removed

Returns:

true if the child was present