Javascript
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// Copyright (c) 2011 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
/**
* @fileoverview Card slider implementation. Allows you to create interactions
* that have items that can slide left to right to reveal additional items.
* Works by adding the necessary event handlers to a specific DOM structure
* including a frame, container and cards.
* - The frame defines the boundary of one item. Each card will be expanded to
* fill the width of the frame. This element is also overflow hidden so that
* the additional items left / right do not trigger horizontal scrolling.
* - The container is what all the touch events are attached to. This element
* will be expanded to be the width of all cards.
* - The cards are the individual viewable items. There should be one card for
* each item in the list. Only one card will be visible at a time. Two cards
* will be visible while you are transitioning between cards.
*
* This class is designed to work well on any hardware-accelerated touch device.
* It should still work on pre-hardware accelerated devices it just won't feel
* very good. It should also work well with a mouse.
*/
// Use an anonymous function to enable strict mode just for this file (which
// will be concatenated with other files when embedded in Chrome
var Slider = (function() {
'use strict';
/**
* @constructor
* @param {!Element} frame The bounding rectangle that cards are visible in.
* @param {!Element} container The surrounding element that will have event
* listeners attached to it.
* @param {!Array.<!Element>} cards The individual viewable cards.
* @param {number} currentCard The index of the card that is currently
* visible.
* @param {number} cardWidth The width of each card should have.
*/
function Slider(frame, container, cards, currentCard, cardWidth) {
/**
* @type {!Element}
* @private
*/
this.frame_ = frame;
/**
* @type {!Element}
* @private
*/
this.container_ = container;
/**
* @type {!Array.<!Element>}
* @private
*/
this.cards_ = cards;
/**
* @type {number}
* @private
*/
this.currentCard_ = currentCard;
/**
* @type {number}
* @private
*/
this.cardWidth_ = cardWidth;
/**
* @type {!TouchHandler}
* @private
*/
this.touchHandler_ = new TouchHandler(this.container_);
}
/**
* Events fired by the slider.
* Events are fired at the container.
*/
Slider.EventType = {
// Fired when the user slides to another card.
CARD_CHANGED: 'slider:card_changed'
};
/**
* The time to transition between cards when animating. Measured in ms.
* @type {number}
* @private
* @const
*/
Slider.TRANSITION_TIME_ = 200;
/**
* The minimum velocity required to transition cards if they did not drag past
* the halfway point between cards. Measured in pixels / ms.
* @type {number}
* @private
* @const
*/
Slider.TRANSITION_VELOCITY_THRESHOLD_ = 0.2;
Slider.prototype = {
/**
* The current left offset of the container relative to the frame.
* @type {number}
* @private
*/
currentLeft_: 0,
/**
* Initialize all elements and event handlers. Must call after construction
* and before usage.
*/
initialize: function() {
var view = this.container_.ownerDocument.defaultView;
assert(view.getComputedStyle(this.container_).display == '-webkit-box',
'Container should be display -webkit-box.');
assert(view.getComputedStyle(this.frame_).overflow == 'hidden',
'Frame should be overflow hidden.');
assert(view.getComputedStyle(this.container_).position == 'static',
'Container should be position static.');
for (var i = 0, card; card = this.cards_[i]; i++) {
assert(view.getComputedStyle(card).position == 'static',
'Cards should be position static.');
}
this.updateCardWidths_();
this.transformToCurrentCard_();
this.container_.addEventListener(TouchHandler.EventType.TOUCH_START,
this.onTouchStart_.bind(this));
this.container_.addEventListener(TouchHandler.EventType.DRAG_START,
this.onDragStart_.bind(this));
this.container_.addEventListener(TouchHandler.EventType.DRAG_MOVE,
this.onDragMove_.bind(this));
this.container_.addEventListener(TouchHandler.EventType.DRAG_END,
this.onDragEnd_.bind(this));
this.touchHandler_.enable(/* opt_capture */ false);
},
/**
* Use in cases where the width of the frame has changed in order to update
* the width of cards. For example should be used when orientation changes
* in full width sliders.
* @param {number} newCardWidth Width all cards should have, in pixels.
*/
resize: function(newCardWidth) {
if (newCardWidth != this.cardWidth_) {
this.cardWidth_ = newCardWidth;
this.updateCardWidths_();
// Must upate the transform on the container to show the correct card.
this.transformToCurrentCard_();
}
},
/**
* Sets the cards used. Can be called more than once to switch card sets.
* @param {!Array.<!Element>} cards The individual viewable cards.
* @param {number} index Index of the card to in the new set of cards to
* navigate to.
*/
setCards: function(cards, index) {
assert(index >= 0 && index < cards.length,
'Invalid index in Slider#setCards');
this.cards_ = cards;
this.updateCardWidths_();
// Jump to the given card index.
this.selectCard(index);
},
/**
* Updates the width of each card.
* @private
*/
updateCardWidths_: function() {
for (var i = 0, card; card = this.cards_[i]; i++)
card.style.width = this.cardWidth_ + 'px';
},
/**
* Returns the index of the current card.
* @return {number} index of the current card.
*/
get currentCard() {
return this.currentCard_;
},
/**
* Clear any transition that is in progress and enable dragging for the
* touch.
* @param {!TouchHandler.Event} e The TouchHandler event.
* @private
*/
onTouchStart_: function(e) {
this.container_.style.WebkitTransition = '';
e.enableDrag = true;
},
/**
* Tell the TouchHandler that dragging is acceptable when the user begins by
* scrolling horizontally.
* @param {!TouchHandler.Event} e The TouchHandler event.
* @private
*/
onDragStart_: function(e) {
e.enableDrag = Math.abs(e.dragDeltaX) > Math.abs(e.dragDeltaY);
},
/**
* On each drag move event reposition the container appropriately so the
* cards look like they are sliding.
* @param {!TouchHandler.Event} e The TouchHandler event.
* @private
*/
onDragMove_: function(e) {
var deltaX = e.dragDeltaX;
// If dragging beyond the first or last card then apply a backoff so the
// dragging feels stickier than usual.
if (!this.currentCard && deltaX > 0 ||
this.currentCard == (this.cards_.length - 1) && deltaX < 0) {
deltaX /= 2;
}
this.translateTo_(this.currentLeft_ + deltaX);
},
/**
* Moves the view to the specified position.
* @param {number} x Horizontal position to move to.
* @private
*/
translateTo_: function(x) {
// We use a webkitTransform to slide because this is GPU accelerated on
// Chrome and iOS. Once Chrome does GPU acceleration on the position
// fixed-layout elements we could simply set the element's position to
// fixed and modify 'left' instead.
this.container_.style.WebkitTransform = 'translate3d(' + x + 'px, 0, 0)';
},
/**
* On drag end events we may want to transition to another card, depending
* on the ending position of the drag and the velocity of the drag.
* @param {!TouchHandler.Event} e The TouchHandler event.
* @private
*/
onDragEnd_: function(e) {
var deltaX = e.dragDeltaX;
var velocity = this.touchHandler_.getEndVelocity().x;
var newX = this.currentLeft_ + deltaX;
var newCardIndex = Math.round(-newX / this.cardWidth_);
if (newCardIndex == this.currentCard && Math.abs(velocity) >
Slider.TRANSITION_VELOCITY_THRESHOLD_) {
// If the drag wasn't far enough to change cards but the velocity was
// high enough to transition anyways. If the velocity is to the left
// (negative) then the user wishes to go right (card +1).
newCardIndex += velocity > 0 ? -1 : 1;
}
this.selectCard(newCardIndex, /* animate */ true);
},
/**
* Cancel any current touch/slide as if we saw a touch end
*/
cancelTouch: function() {
// Stop listening to any current touch
this.touchHandler_.cancelTouch();
// Ensure we're at a card bounary
this.transformToCurrentCard_(true);
},
/**
* Selects a new card, ensuring that it is a valid index, transforming the
* view and possibly calling the change card callback.
* @param {number} newCardIndex Index of card to show.
* @param {boolean=} opt_animate If true will animate transition from
* current position to new position.
*/
selectCard: function(newCardIndex, opt_animate) {
var isChangingCard = newCardIndex >= 0 &&
newCardIndex < this.cards_.length &&
newCardIndex != this.currentCard;
if (isChangingCard) {
// If we have a new card index and it is valid then update the left
// position and current card index.
this.currentCard_ = newCardIndex;
}
this.transformToCurrentCard_(opt_animate);
if (isChangingCard) {
var event = document.createEvent('Event');
event.initEvent(Slider.EventType.CARD_CHANGED, true, true);
event.slider = this;
this.container_.dispatchEvent(event);
}
},
/**
* Centers the view on the card denoted by this.currentCard. Can either
* animate to that card or snap to it.
* @param {boolean=} opt_animate If true will animate transition from
* current position to new position.
* @private
*/
transformToCurrentCard_: function(opt_animate) {
this.currentLeft_ = -this.currentCard * this.cardWidth_;
// Animate to the current card, which will either transition if the
// current card is new, or reset the existing card if we didn't drag
// enough to change cards.
var transition = '';
if (opt_animate) {
transition = '-webkit-transform ' + Slider.TRANSITION_TIME_ +
'ms ease-in-out';
}
this.container_.style.WebkitTransition = transition;
this.translateTo_(this.currentLeft_);
}
};
return Slider;
})();