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.

Panel

public Panel()

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

adopt

protected final void adopt(Widget child)

Finalize the attachment of a Widget to this Panel. This method is the last step in adding or inserting a Widget into a Panel, and should be called after physical attachment in the DOM is complete. This Panel becomes the parent of the child Widget, and the child will now fire its Widget.onAttach() event if this Panel is currently attached.

Parameters:

child - the widget to be adopted

See Also:

add(Widget)

adopt

@Deprecated
protected void adopt(Widget w,
                                Element container)

Deprecated. Use adopt(Widget).

This method was formerly part of the process of adding a Widget to a Panel but has been deprecated in favor of adopt(Widget).

disown

@Deprecated
protected void disown(Widget w)

Deprecated. Use orphan(Widget).

This method was formerly part of the process of removing a Widget from a Panel but has been deprecated in favor of orphan(Widget).

doAttachChildren

protected void doAttachChildren()

Description copied from class: Widget

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 Widget.onAttach() for each of its child widgets.

Overrides:

doAttachChildren in class Widget

See Also:

Widget.onAttach()

doDetachChildren

protected void doDetachChildren()

Description copied from class: Widget

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 Widget.onDetach() for each of its child widgets.

Overrides:

doDetachChildren in class Widget

See Also:

Widget.onDetach()

onLoad

protected void onLoad()

A Panel's onLoad method will be called after all of its children are attached.

Overrides:

onLoad in class Widget

See Also:

Widget.onLoad()

onUnload

protected void onUnload()

A Panel's onUnload method will be called before its children become detached themselves.

Overrides:

onUnload in class Widget

See Also:

Widget.onLoad()

orphan

protected final void orphan(Widget child)

This method must be called as part of the remove method of any Panel. It ensures that the Widget's parent is cleared. This method should be called after verifying that the child Widget is an existing child of the Panel, but before physically removing the child Widget from the DOM. The child will now fire its Widget.onDetach() event if this Panel is currently attached.

Calls to orphan(Widget) should be wrapped in a try/finally block to ensure that the widget is physically detached even if orphan throws an exception.

Parameters:

child - the widget to be disowned

See Also:

add(Widget)