com.google.livingstories.client.ui.AnchoredPanel.java Source code

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Here is the source code for com.google.livingstories.client.ui.AnchoredPanel.java

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/**
 * Copyright 2010 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.livingstories.client.ui;

import com.google.gwt.dom.client.Element;
import com.google.gwt.dom.client.Style;
import com.google.gwt.event.logical.shared.ResizeEvent;
import com.google.gwt.event.logical.shared.ResizeHandler;
import com.google.gwt.event.shared.HandlerRegistration;
import com.google.gwt.user.client.Window;
import com.google.gwt.user.client.Window.ScrollEvent;
import com.google.gwt.user.client.Window.ScrollHandler;
import com.google.gwt.user.client.ui.SimplePanel;
import com.google.gwt.user.client.ui.Widget;

/**
 * Panel that makes its contents scroll with the page.
 * However, the scrollable area is bounded by the box defined by this panel.
 * When the content hits a boundary, it will stop scrolling.
 */
public class AnchoredPanel extends SimplePanel {
    private boolean scrolling;
    private HandlerRegistration scrollHandler;
    private HandlerRegistration resizeHandler;

    @Override
    public void setWidget(Widget widget) {
        super.setWidget(widget);
        Style style = widget.getElement().getStyle();
        style.setProperty("position", "relative");
        style.setPropertyPx("left", 0);
        style.setPropertyPx("top", 0);

        removeHandlers();

        scrollHandler = Window.addWindowScrollHandler(new ScrollHandler() {
            @Override
            public void onWindowScroll(ScrollEvent event) {
                reposition();
            }
        });

        resizeHandler = Window.addResizeHandler(new ResizeHandler() {
            @Override
            public void onResize(ResizeEvent event) {
                reposition();
            }
        });
    }

    public void remove() {
        super.clear();
        removeHandlers();
    }

    private void removeHandlers() {
        if (scrollHandler != null) {
            scrollHandler.removeHandler();
            scrollHandler = null;
        }
        if (resizeHandler != null) {
            resizeHandler.removeHandler();
            resizeHandler = null;
        }
    }

    public void reposition() {
        Widget content = getWidget();
        Element boundingBox = getElement().getParentElement();
        int windowTop = Window.getScrollTop();
        int windowLeft = Window.getScrollLeft();
        int topBound = boundingBox.getAbsoluteTop();
        int bottomBound = topBound + boundingBox.getOffsetHeight() - content.getOffsetHeight();
        if (!scrolling) {
            if (windowTop > topBound && windowTop < bottomBound) {
                scrolling = true;
                Style style = content.getElement().getStyle();
                style.setProperty("position", "fixed");
                style.setPropertyPx("top", 0);
                style.setPropertyPx("left", boundingBox.getAbsoluteLeft() - windowLeft);
            }
        } else {
            if (windowTop < topBound) {
                scrolling = false;
                Style style = content.getElement().getStyle();
                style.setProperty("position", "relative");
                style.setPropertyPx("top", 0);
                style.setPropertyPx("left", 0);
            } else if (windowTop > bottomBound) {
                scrolling = false;
                Style style = content.getElement().getStyle();
                style.setProperty("position", "relative");
                // Can't use bottom:0px here because the spacer has no height.
                // Even if we set the spacer's height to be 100%, it won't necessarily
                // work if this panel is in a table cell.
                style.setPropertyPx("top", bottomBound - topBound);
                style.setPropertyPx("left", 0);
            } else {
                content.getElement().getStyle().setPropertyPx("left", boundingBox.getAbsoluteLeft() - windowLeft);
            }
        }
    }
}