import { mark, stop } from '../../_utils/marks' import { RealmStore } from '../../_utils/RealmStore' import { reselect } from '../../_utils/reselect' const RENDER_BUFFER_FACTOR = 2.5 class VirtualListStore extends RealmStore { constructor (state) { super(state, /* maxSize */ 10) } } const virtualListStore = new VirtualListStore() virtualListStore.computeForRealm('items', null) virtualListStore.computeForRealm('showFooter', false) virtualListStore.computeForRealm('footerHeight', 0) virtualListStore.computeForRealm('showHeader', false) virtualListStore.computeForRealm('headerHeight', 0) virtualListStore.computeForRealm('scrollTop', 0) virtualListStore.computeForRealm('scrollHeight', 0) virtualListStore.computeForRealm('offsetHeight', 0) virtualListStore.computeForRealm('listOffset', 0) virtualListStore.computeForRealm('itemHeights', {}) virtualListStore.compute('rawVisibleItems', ['items', 'scrollTop', 'itemHeights', 'offsetHeight', 'showHeader', 'headerHeight', 'listOffset'], (items, scrollTop, itemHeights, offsetHeight, showHeader, headerHeight, listOffset) => { window.rawVisibleItemsComputed = (window.rawVisibleItemsComputed || 0) + 1 mark('compute visibleItems') if (!items) { return null } let effectiveScrollTop = scrollTop - listOffset let renderBuffer = RENDER_BUFFER_FACTOR * offsetHeight let visibleItems = [] let totalOffset = showHeader ? headerHeight : 0 let len = items.length let i = -1 while (++i < len) { let key = items[i] let height = itemHeights[key] || 0 let currentOffset = totalOffset totalOffset += height let isAboveViewport = (currentOffset < effectiveScrollTop) if (isAboveViewport) { if ((effectiveScrollTop - height - renderBuffer) > currentOffset) { continue // above the area we want to render } } else { if (currentOffset > (effectiveScrollTop + offsetHeight + renderBuffer)) { break // below the area we want to render } } visibleItems.push({ offset: currentOffset, key: key, index: i }) } stop('compute visibleItems') return visibleItems }) reselect(virtualListStore, 'visibleItems', 'rawVisibleItems') virtualListStore.compute('heightWithoutFooter', ['items', 'itemHeights', 'showHeader', 'headerHeight'], (items, itemHeights, showHeader, headerHeight) => { if (!items) { return 0 } let sum = showHeader ? headerHeight : 0 let i = -1 let len = items.length while (++i < len) { sum += itemHeights[items[i]] || 0 } return sum }) virtualListStore.compute('height', ['heightWithoutFooter', 'showFooter', 'footerHeight'], (heightWithoutFooter, showFooter, footerHeight) => { return showFooter ? (heightWithoutFooter + footerHeight) : heightWithoutFooter }) virtualListStore.compute('length', ['items'], (items) => items ? items.length : 0) virtualListStore.compute('allVisibleItemsHaveHeight', ['visibleItems', 'itemHeights'], (visibleItems, itemHeights) => { if (!visibleItems) { return false } for (let visibleItem of visibleItems) { if (!itemHeights[visibleItem.key]) { return false } } return true }) if (process.browser && process.env.NODE_ENV !== 'production') { window.virtualListStore = virtualListStore virtualListStore.observe('visibleItems', () => { window.visibleItemsChangedCount = (window.visibleItemsChangedCount || 0) + 1 }) virtualListStore.observe('rawVisibleItems', () => { window.rawVisibleItemsChangedCount = (window.rawVisibleItemsChangedCount || 0) + 1 }) } export { virtualListStore }