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/*
 * Copyright 2007 Google Inc.
 * 
 * Licensed under the Apache License, Version 2.0 (the "License"); you may not
 * use this file except in compliance with the License. You may obtain a copy of
 * the License at
 * 
 * http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
 * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
 * License for the specific language governing permissions and limitations under
 * the License.
 */
package com.google.gwt.user.client.ui;

import java.util.Iterator;

/**
 * Abstract base class for all panels, which are widgets that can contain other
 * widgets.
 */
public abstract class Panel extends Widget implements HasWidgets.ForIsWidget {

  /**
   * 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. *
  3. 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 {@link ComplexPanel#adjustIndex(Widget, int)}.
  4. *
  5. Detach Child: Remove the Widget from its existing parent, if * any. Most Panels will simply call {@link Widget#removeFromParent()} on the * Widget.
  6. *
  7. 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 {@link WidgetCollection} at the appropriate index.
  8. *
  9. Physical Attach: The Widget's Element must be physically * attached to the Panel's Element, either directly or indirectly.
  10. *
  11. Adopt: Call {@link #adopt(Widget)} to finalize the add as the * very last step.
  12. *
*

* * @param child the widget to be added * @throws UnsupportedOperationException if this method is not supported (most * often this means that a specific overload must be called) * @see HasWidgets#add(Widget) */ public void add(Widget child) { throw new UnsupportedOperationException( "This panel does not support no-arg add()"); } public void add(IsWidget child) { this.add(asWidgetOrNull(child)); } public void clear() { Iterator it = iterator(); while (it.hasNext()) { it.next(); it.remove(); } } /** * 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. *
  3. Orphan: Call {@link #orphan(Widget)} first while the child * Widget is still attached.
  4. *
  5. 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.
  6. *
  7. 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 {@link WidgetCollection}.
  8. *
*

* * @param child the widget to be removed * @return true if the child was present */ public abstract boolean remove(Widget child); public boolean remove(IsWidget child) { return remove(asWidgetOrNull(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 * {@link Widget#onAttach()} event if this Panel is currently attached. * * @param child the widget to be adopted * @see #add(Widget) */ protected final void adopt(Widget child) { assert (child.getParent() == null); child.setParent(this); } @Override protected void doAttachChildren() { AttachDetachException.tryCommand(this, AttachDetachException.attachCommand); } @Override protected void doDetachChildren() { AttachDetachException.tryCommand(this, AttachDetachException.detachCommand); } /** *

* 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 {@link Widget#onDetach()} event if this Panel is * currently attached. *

*

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

* * @param child the widget to be disowned * @see #add(Widget) */ protected final void orphan(Widget child) { assert (child.getParent() == this); child.setParent(null); } }




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