com.google.gwt.user.client.ui.ScrollImpl Maven / Gradle / Ivy
/*
* Copyright 2011 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.core.client.GWT;
import com.google.gwt.dom.client.Document;
import com.google.gwt.dom.client.Element;
/**
* Implementation of scrolling behavior.
*/
class ScrollImpl {
/**
* IE does not fire a scroll event when the scrollable element or the
* container is resized, so we synthesize one as needed. IE scrolls in the
* positive direction, even in RTL mode.
*/
static class ScrollImplTrident extends ScrollImpl {
private static void triggerScrollEvent(Element elem) {
elem.dispatchEvent(Document.get().createScrollEvent());
}
@Override
public native void initialize(Element scrollable, Element container) /*-{
// Remember the last scroll position.
var scrollableElem = scrollable;
scrollableElem.__lastScrollTop = scrollableElem.__lastScrollLeft = 0;
var scrollHandler = $entry(function() {
scrollableElem.__lastScrollTop = scrollableElem.scrollTop;
scrollableElem.__lastScrollLeft = scrollableElem.scrollLeft;
});
scrollable.attachEvent('onscroll', scrollHandler);
// Detect if the scrollable element or the container within it changes
// size, either of which could affect the scroll position.
var resizeHandler = $entry(function() {
// Give the browser a chance to fire a native scroll event before
// synthesizing one.
setTimeout($entry(function() {
// Trigger a synthetic scroll event if the scroll position changes.
if (scrollableElem.scrollTop != scrollableElem.__lastScrollTop ||
scrollableElem.scrollLeft != scrollableElem.__lastScrollLeft) {
scrollHandler(); // Update scroll positions.
@com.google.gwt.user.client.ui.ScrollImpl.ScrollImplTrident::triggerScrollEvent(Lcom/google/gwt/dom/client/Element;)
(scrollableElem);
}
}), 1);
});
scrollable.attachEvent('onresize', resizeHandler);
container.attachEvent('onresize', resizeHandler);
}-*/;
@Override
public native boolean isRtl(Element scrollable) /*-{
return scrollable.currentStyle.direction == 'rtl';
}-*/;
}
private static ScrollImpl impl;
/**
* Get the singleton instance of {@link ScrollImpl}.
*/
static ScrollImpl get() {
if (impl == null) {
impl = GWT.create(ScrollImpl.class);
}
return impl;
}
/**
* Get the maximum horizontal scroll position.
*
* @param scrollable the scrollable element
* @return the maximum scroll position
*/
public int getMaximumHorizontalScrollPosition(Element scrollable) {
return isRtl(scrollable) ? 0 : scrollable.getScrollWidth() - scrollable.getClientWidth();
}
/**
* Get the minimum horizontal scroll position.
*
* @param scrollable the scrollable element
* @return the minimum scroll position
*/
public int getMinimumHorizontalScrollPosition(Element scrollable) {
return isRtl(scrollable) ? scrollable.getClientWidth() - scrollable.getScrollWidth() : 0;
}
/**
* Initialize a scrollable element.
*
* @param scrollable the scrollable element
* @param container the container
*/
public void initialize(Element scrollable, Element container) {
// Overridden by ScrollImplTrident.
}
/**
* Check if the specified element has an RTL direction. We can't base this on
* the current locale because the user can modify the direction at the DOM
* level.
*
* @param scrollable the scrollable element
* @return true if the direction is RTL, false if LTR
*/
public native boolean isRtl(Element scrollable) /*-{
var computedStyle = $doc.defaultView.getComputedStyle(scrollable, null);
return computedStyle.getPropertyValue('direction') == 'rtl';
}-*/;
}