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polymer-virtual-list.html
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polymer-virtual-list.html
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<!--
Copyright 2013 The Polymer Authors. All rights reserved.
Use of this source code is governed by a BSD-style
license that can be found in the LICENSE file.
-->
<link rel="import" href="../polymer/polymer.html">
<polymer-element name="polymer-virtual-list" attributes="count pageSize numPages horizontal fixedHeight">
<template>
<link rel="stylesheet" href="polymer-virtual-list.css">
<div id="list" class="polymer-list-list">
<div id="viewport" class="polymer-list-viewport"></div>
</div>
</template>
<script>
Polymer('polymer-virtual-list', {
// rows per page
pageSize: 20,
// number of pages
numPages: 2,
// total number of rows
count: 0,
// number of pages to render at start
numInitialPages: 0,
horizontal: false,
fixedHeight: false,
retainPages: false,
observe: {
count: 'refresh',
pageSize: 'reset',
numPages: 'reset',
retainPages: 'reset',
horizontal: 'reset'
},
ready: function() {
this.setupScrollListener();
this.reset();
},
setupScrollListener: function() {
var self = this;
this.$.list.addEventListener('scroll', function(e) {
self.scroll(e);
})
},
// re-render at the top
reset: function() {
this.initialized = false;
// discover dimensionality
this.$.viewport.classList.toggle('horizontal', this.horizontal);
this.updateMetrics();
// clear size estimate caches
this.rowHeight = 0;
this.pageHeights = [];
this.pageTops = [];
// scroll to top!
this.scrollOffset = 0;
this.refresh();
},
// completely refresh rendering at the current scroll position
refresh: function() {
this.pageCount = Math.ceil(this.count/this.pageSize);
this.$.viewport.textContent = '';
this.pages = [];
this.pageCache = [];
// completely invalidate rendering
this.invalidatePages(this.getViewportPageInfo());
},
// adjust viewport height when page count changes...
pageCountChanged: function(oldValue) {
if (this.initialized && oldValue) {
var h = 0, delta = this.pageCount - oldValue;
if (delta > 0) {
h = (delta-1) * this.getPageHeight(this.pageCount-1);
} else {
for (var i=oldValue-1; i >= this.pageCount; i--) {
h -= this.getPageHeight(i);
}
}
this.viewportHeight += h;
}
},
updateMetrics: function() {
var h = this.horizontal;
this.metrics = {
scrollOffset: h ? 'scrollLeft' : 'scrollTop',
offsetExtent: h ? 'offsetWidth' : 'offsetHeight',
offsetPosition: h ? 'offsetLeft' : 'offsetTop',
extent: h ? 'width' : 'height',
position: h ? 'left' : 'top'
};
},
// get the current scrollOffset
get scrollOffset() {
return this.$.list[this.metrics.scrollOffset];
},
// sets the current scrollOffset
set scrollOffset(offset) {
this.$.list[this.metrics.scrollOffset] = offset;
},
generatePageContent: function(page, start, end) {
this.fire('polymer-list-generate-page',
{page: page, start: start, end: end});
},
generatePage: function(pageNum) {
if (pageNum < this.pageCount) {
var p = document.createElement('div');
p.pageNum = pageNum;
p.setAttribute('page', pageNum);
if (this.retainPages) {
p.style.display = 'none';
}
var start = p.pageNum * this.pageSize;
var end = Math.min(start + this.pageSize, this.count);
this.generatePageContent(p, start, end);
this.$.viewport.appendChild(p);
this.pageCache[pageNum] = p;
if (this.fixedHeight) {
this.pageTops[pageNum] = null;
this.positionPage(p);
}
return p;
}
},
initialize: function(pageHeight, pageNumber) {
this.rowHeight = pageHeight/(this.pageSize < this.count ?
this.pageSize : this.count);
this.viewportHeight = this.count * this.rowHeight;
var numPages = Math.min(Math.ceil(this.count / this.pageSize),
this.numInitialPages);
for (var i = 0; i < numPages; i++) {
if (pageNumber !== i) {
this.generatePage(i);
}
}
this.initialized = true;
},
get viewportHeight() {
return this._viewportHeight;
},
set viewportHeight(value) {
this._viewportHeight = value;
this.$.viewport.style[this.metrics.extent] = this._viewportHeight + 'px';
},
calcPageHeight: function(page) {
return (this.fixedHeight && this.rowHeight) ?
(this.pageSize * this.rowHeight) : page[this.metrics.offsetExtent];
},
getPageHeight: function(pageNum) {
return this.pageHeights[pageNum] !== undefined ?
this.pageHeights[pageNum] :
this.pageSize * (this.rowHeight || 100);
},
// calculates the start and center page for the current scroll position
getViewportPageInfo: function() {
var c = Math.floor(this.locatePage(this.scrollOffset +
this.$.list[this.metrics.offsetExtent]/2) + 0.5);
var k = c - Math.floor(this.numPages/2);
k = Math.max(0, k);
// the current start/center page index
return {start: k, center: c};
},
// given a positon, returns page number + decimal offset on page.
locatePage: function(pos) {
// guesstimate page given 1st page's height
var pn = pos/this.getPageHeight(0);
if (this.fixedHeight) {
return pn;
}
pn = Math.floor(pn);
// decrement page if the pageTop of guesstimate is > requested pos
while (pn && !this.pageTops[pn] || (this.pageTops[pn] > pos)) {
pn--;
}
var pt = this.pageTops[pn] || 0;
// increment page if pageTop of guesstimate is < requested pos
// also adjust the pageTops for any interrogated page
while (pos >= pt) {
pt += this.getPageHeight(pn++);
this.pageTops[pn] = pt;
}
// find decimal offset on page
pn--;
var ph = this.getPageHeight(pn);
return pn + (pos-pt+ph)/ph;
},
/* returns delta between actual and expected */
measurePage: function(page) {
var ph = this.calcPageHeight(page);
var pn = page.pageNum;
if (!this.rowHeight) {
// rowHeight is not set, use the page's height to setup initial values
this.initialize(ph, pn);
}
var ph0 = this.getPageHeight(pn);
if (ph && ph0 != ph) {
this.pageHeights[pn] = ph;
// since page height has changed, invalidate all the pageTops after
// this page
this.pageTops.splice(pn+1, this.pageTops.length);
// also adjust the viewport's height
return ph - ph0;
}
return 0;
},
// positions the given page and returns the adjustment delta.
positionPage: function(page) {
var pn = page.pageNum, t;
if (this.fixedHeight) {
t = pn * this.rowHeight * this.pageSize;
if (!this.pageTops[pn]) {
this.pageTops[pn] = t;
page.style[this.metrics.position] = t + 'px';
}
return 0;
} else {
t = this.pageTops[pn] ? this.pageTops[pn] : this.calcPageTop(pn);
// update pageTops cache
this.pageTops[pn] = t;
this.pageTops[pn+1] = t + this.getPageHeight(pn);
// save old top
var t0 = page.style[this.metrics.position].slice(0, -2);
// set the page's top
page.style[this.metrics.position] = t + 'px';
//page.style.webkitTransform = 'translate3d(0, ' + t + 'px, 0)';
// return delta between old and new
if (t0) {
return t0 - t;
}
}
},
// calculate a pageTop from scratch by iterating from the top
// NOTE: this is costly, but we almost never need to do this
// because of the pageTop setting done by locatePage
calcPageTop: function(pageNum) {
var n = 0, t=0;
while (n < pageNum) {
t += this.getPageHeight(n);
n++;
}
return t;
},
// use cache if pages are retained because in this case we expect
// querySelector to be slow!
findPage: function(pageNum) {
if (!this.retainPages || !this.pageCache[pageNum]) {
this.pageCache[pageNum] = this.$.viewport.querySelector(
'[page="' + pageNum + '"]');
}
return this.pageCache[pageNum];
},
/*
TODO(sorvell): chrome fires scroll events with raf timing;
on other browser, we will want to throttle events to that timing
*/
scroll: function(e) {
this.fire('polymer-list-scroll');
var info = this.getViewportPageInfo();
// validate if needed
if (!this.pages[0] || this.pages[0].pageNum != info.start) {
this.invalidatePages(info);
}
},
// extension point for customizing page setup
invalidatePages: function(info) {
this.invalidate(info);
},
// validate rendering at the given or current scroll position
invalidate: function(info) {
info = info || this.getViewportPageInfo();
var k = info.start, n = info.start+this.numPages,
c = info.center, v=0, s=0, d;
this.previousPages = this.pages;
this.pages = [];
for (; k<n; k++) {
var p = this.findPage(k) || this.generatePage(k);
if (p) {
if (this.retainPages) {
p.style.display = null;
}
v += this.measurePage(p);
d = this.positionPage(p);
// adjust scrollOffset if center page's top has changed
if (d && k === c) {
s = d;
}
this.pages.push(p);
}
}
// adjust viewport and scroll position iff needed
if (!this.fixedHeight) {
if (v) {
this.viewportHeight += v;
}
if (s) {
this.scrollOffset -= s;
}
}
// remove out-of-bounds pages
this.cleanupPages();
},
cleanupPages: function() {
var p$ = this.previousPages;
for (var i=0, l=p$.length, p; (i<l) && (p=p$[i]); i++) {
if (this.pages.indexOf(p) == -1) {
if (this.retainPages) {
p.style.display = 'none';
} else {
this.$.viewport.removeChild(p);
}
}
}
},
// setting scrollOffset is asynchronous; this method provides
// a way to scroll the list synchronously.
setScrollOffsetImmediate: function(pos){
this.scrollOffset = pos;
this.scroll();
},
scrollToRow: function(row) {
row = Math.max(0, Math.min(row, this.count-1));
// find page and row in page
var pageNum = Math.floor(row / this.pageSize);
// guesstimate offset and scroll to it
var top = this.pageTops[pageNum] || this.calcPageTop(pageNum);
this.setScrollOffsetImmediate(top);
// re-scroll with updated info
var top = this.pageTops[pageNum];
this.setScrollOffsetImmediate(top);
// scroll to offset on this page
var page = this.findPage(pageNum);
var rowInPage = row - pageNum * this.pageSize;
this.whenNodeFoundOnPage(page, rowInPage, function(node) {
this.setScrollOffsetImmediate(this.scrollOffset +
node[this.metrics.offsetPosition]);
});
},
// note: may need to go async to find node
whenNodeFoundOnPage: function(page, index, callback) {
var node = this.findRowOnPage(page, index, callback);
if (node) {
callback.call(this, node);
} else {
this.onMutation(this.mutationNodeForPage(page), function() {
this.whenNodeFoundOnPage(page, index, callback);
})
}
},
mutationNodeForPage: function(page) {
return page;
},
findRowOnPage: function(page, index) {
return page.children[index];
}
});
</script>
</polymer-element>