com.google.gwt.user.client.ui.RootLayoutPanel.java Source code

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Here is the source code for com.google.gwt.user.client.ui.RootLayoutPanel.java

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/*
 * Copyright 2009 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.event.logical.shared.ResizeEvent;
import com.google.gwt.event.logical.shared.ResizeHandler;
import com.google.gwt.user.client.Window;

/**
 * A singleton implementation of {@link LayoutPanel} that always attaches itself
 * to the document body (i.e. {@link RootPanel#get()}).
 * 
 * <p>
 * This panel automatically calls {@link RequiresResize#onResize()} on itself
 * when initially created, and whenever the window is resized.
 * </p>
 * 
 * <p>
 * NOTE: This widget will <em>only</em> work in standards mode, which requires
 * that the HTML page in which it is run have an explicit &lt;!DOCTYPE&gt;
 * declaration.
 * </p>
 * 
 * <p>
 * <h3>Example</h3>
 * {@example com.google.gwt.examples.LayoutPanelExample}
 * </p>
 */
public class RootLayoutPanel extends LayoutPanel {

    private static RootLayoutPanel singleton;

    /**
     * Gets the singleton instance of RootLayoutPanel. This instance will always
     * be attached to the document body via {@link RootPanel#get()}.
     * 
     * <p>
     * Note that, unlike {@link RootPanel#get(String)}, this class provides no way
     * to get an instance for any element on the page other than the document
     * body. This is because we know of no way to get resize events for anything
     * but the window.
     * </p>
     */
    public static RootLayoutPanel get() {
        if (singleton == null) {
            singleton = new RootLayoutPanel();
            RootPanel.get().add(singleton);
        }
        return singleton;
    }

    private RootLayoutPanel() {
        Window.addResizeHandler(new ResizeHandler() {
            public void onResize(ResizeEvent event) {
                RootLayoutPanel.this.onResize();
            }
        });

        // TODO(jgw): We need notification of font-size changes as well.
        // I believe there's a hidden iframe trick that we can use to get
        // a font-size-change event (really an em-definition-change event).
    }

    @Override
    protected void onLoad() {
        getLayout().onAttach();
        getLayout().fillParent();
    }
}