/*
* Copyright 2006 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 com.google.gwt.user.client.DOM;
import com.google.gwt.user.client.Element;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.WindowCloseListener;
import java.util.HashMap;
import java.util.Iterator;
/**
* The panel to which all other widgets must ultimately be added. RootPanels are
* never created directly. Rather, they are accessed via {@link RootPanel#get()}.
*
* <p>
* Most applications will add widgets to the default root panel in their
* {@link com.google.gwt.core.client.EntryPoint#onModuleLoad} methods.
* </p>
*/
public class RootPanel extends AbsolutePanel {
private static HashMap rootPanels = new HashMap();
/**
* Gets the default root panel. This panel wraps body of the browser's
* document. This root panel can contain any number of widgets, which will be
* laid out in their natural HTML ordering. Many applications, however, will
* add a single panel to the RootPanel to provide more structure.
*
* @return the default RootPanel
*/
public static RootPanel get() {
return get(null);
}
/**
* Gets the root panel associated with a given browser element. For this to
* work, the HTML document into which the application is loaded must have
* specified an element with the given id.
*
* @param id the id of the element to be wrapped with a root panel
* @return the root panel, or <code>null</code> if no such element was found
*/
public static RootPanel get(String id) {
// See if this RootPanel is already created.
RootPanel gwt = (RootPanel) rootPanels.get(id);
if (gwt != null) {
return gwt;
}
// Find the element that this RootPanel will wrap.
Element elem = null;
if (id != null) {
if (null == (elem = DOM.getElementById(id))) {
return null;
}
}
if (rootPanels.size() == 0) {
hookWindowClosing();
}
// Create the panel and put it in the map.
rootPanels.put(id, gwt = new RootPanel(elem));
return gwt;
}
/**
* Convenience method for getting the document's body element.
*
* @return the document's body element
*/
public static native Element getBodyElement() /*-{
return $doc.body;
}-*/;
private static void hookWindowClosing() {
// Catch the window closing event.
Window.addWindowCloseListener(new WindowCloseListener() {
public void onWindowClosed() {
// When the window is closing, detach all root panels. This will cause
// all of their children's event listeners to be unhooked, which will
// avoid potential memory leaks.
for (Iterator it = rootPanels.values().iterator(); it.hasNext();) {
RootPanel gwt = (RootPanel) it.next();
if (gwt.isAttached()) {
gwt.onDetach();
}
}
}
public String onWindowClosing() {
return null;
}
});
}
private RootPanel(Element elem) {
if (elem == null) {
// 'null' means use document's body element.
elem = getBodyElement();
}
setElement(elem);
onAttach();
}
}