// Copyright 2012 Google Inc. All Rights Reserved.
//
// 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.collide.client.util.dom;
import com.google.collide.client.util.Elements;
import elemental.css.CSSStyleDeclaration;
import elemental.html.Element;
/**
* A class that computes and caches the width of a vertical scrollbar and height
* of a horizontal scrollbar.
*/
public class ScrollbarSizeCalculator {
public static final ScrollbarSizeCalculator INSTANCE = new ScrollbarSizeCalculator();
private int heightOfHorizontalScrollbar = -1;
private int widthOfVerticalScrollbar = -1;
/**
* Calculates (or recalculates) the sizes of the scrollbars.
*/
public void calculateSize() {
Element container = createContainer();
// No scrollbars
container.getStyle().setOverflow(CSSStyleDeclaration.Overflow.HIDDEN);
int noScrollbarClientHeight = container.getClientHeight();
int noScrollbarClientWidth = container.getClientWidth();
// Force scrollbars
container.getStyle().setOverflow(CSSStyleDeclaration.Overflow.SCROLL);
heightOfHorizontalScrollbar = noScrollbarClientHeight - container.getClientHeight();
widthOfVerticalScrollbar = noScrollbarClientWidth - container.getClientWidth();
container.removeFromParent();
}
private Element createContainer() {
Element container = Elements.createDivElement();
final int containerSize = 500;
CSSStyleDeclaration containerStyle = container.getStyle();
containerStyle.setWidth(containerSize, CSSStyleDeclaration.Unit.PX);
containerStyle.setHeight(containerSize, CSSStyleDeclaration.Unit.PX);
containerStyle.setPosition(CSSStyleDeclaration.Position.ABSOLUTE);
containerStyle.setLeft(-containerSize, CSSStyleDeclaration.Unit.PX);
containerStyle.setTop(-containerSize, CSSStyleDeclaration.Unit.PX);
Elements.getBody().appendChild(container);
return container;
}
/**
* Gets the height of a horizontal scrollbar. This will calculate the size if
* it has not already been calculated.
*/
public int getHeightOfHorizontalScrollbar() {
ensureSizeCalculated();
return heightOfHorizontalScrollbar;
}
/**
* Gets the width of a vertical scrollbar. This will calculate the size if it
* has not already been calculated.
*/
public int getWidthOfVerticalScrollbar() {
ensureSizeCalculated();
return widthOfVerticalScrollbar;
}
private void ensureSizeCalculated() {
if (heightOfHorizontalScrollbar < 0 || widthOfVerticalScrollbar < 0) {
calculateSize();
}
}
}