` to ensure the component is rendered
* correctly. Since each custom component's implementation and internals can be
* quite different, wrapping within a `
` is a safe way to make sure
* dimensions are measured correctly.
*
* ```html
*
*
*
* ```
*
*
* ## Virtual Scroll Performance Tips
*
* #### iOS Cordova WKWebView
*
* When deploying to iOS with Cordova, it's highly recommended to use the
* [WKWebView plugin](http://blog.ionic.io/cordova-ios-performance-improvements-drop-in-speed-with-wkwebview/)
* in order to take advantage of iOS's higher performimg webview. Additionally,
* WKWebView is superior at scrolling efficiently in comparision to the older
* UIWebView.
*
* #### Lock in element dimensions and locations
*
* In order for virtual scroll to efficiently size and locate every item, it's
* very important every element within each virtual item does not dynamically
* change its dimensions or location. The best way to ensure size and location
* does not change, it's recommended each virtual item has locked in its size
* via CSS.
*
* #### Use `ion-img` for images
*
* When including images within Virtual Scroll, be sure to use
* [`ion-img`](../img/Img/) rather than the standard `![]()
` HTML element.
* With `ion-img`, images are lazy loaded so only the viewable ones are
* rendered, and HTTP requests are efficiently controlled while scrolling.
*
* #### Set Approximate Widths and Heights
*
* As mentioned above, all elements should lock in their dimensions. However,
* virtual scroll isn't aware of the dimensions until after they have been
* rendered. For the initial render, virtual scroll still needs to set
* how many items should be built. With "approx" property inputs, such as
* `approxItemHeight`, we're able to give virtual sroll an approximate size,
* therefore allowing virtual scroll to decide how many items should be
* created.
*
* #### Changing dataset should use `virtualTrackBy`
*
* It is possible for the identities of elements in the iterator to change
* while the data does not. This can happen, for example, if the iterator
* produced from an RPC to the server, and that RPC is re-run. Even if the
* "data" hasn't changed, the second response will produce objects with
* different identities, and Ionic will tear down the entire DOM and rebuild
* it. This is an expensive operation and should be avoided if possible.
*
* #### Efficient headers and footer functions
*
* Each virtual item must stay extremely efficient, but one way to really
* kill its performance is to perform any DOM operations within section header
* and footer functions. These functions are called for every record in the
* dataset, so please make sure they're performant.
*
*/
@Directive({
selector: '[virtualScroll]'
})
export class VirtualScroll implements DoCheck, AfterContentInit, OnDestroy {
_differ: IterableDiffer;
_scrollSub: any;
_scrollEndSub: any;
_init: boolean;
_lastEle: boolean;
_hdrFn: Function;
_ftrFn: Function;
_records: any[] = [];
_cells: VirtualCell[] = [];
_nodes: VirtualNode[] = [];
_vHeight: number = 0;
_lastCheck: number = 0;
_data: VirtualData = {
scrollTop: 0,
};
_queue: number;
@ContentChild(VirtualItem) _itmTmp: VirtualItem;
@ContentChild(VirtualHeader) _hdrTmp: VirtualHeader;
@ContentChild(VirtualFooter) _ftrTmp: VirtualFooter;
/**
* @input {array} The data that builds the templates within the virtual scroll.
* This is the same data that you'd pass to `*ngFor`. It's important to note
* that when this data has changed, then the entire virtual scroll is reset,
* which is an expensive operation and should be avoided if possible.
*/
@Input()
set virtualScroll(val: any) {
this._records = val;
if (isBlank(this._differ) && isPresent(val)) {
this._differ = this._iterableDiffers.find(val).create(this._cd, this.virtualTrackBy);
}
}
/**
* @input {number} The buffer ratio is used to decide how many cells
* should get created when initially rendered. The number is a
* multiplier against the viewable area's height. For example, if it
* takes `20` cells to fill up the height of the viewable area, then
* with a buffer ratio of `3` it will create `60` cells that are
* available for reuse while scrolling. For better performance, it's
* better to have more cells than what are required to fill the
* viewable area. Default is `3`.
*/
@Input() bufferRatio: number = 3;
/**
* @input {string} The approximate width of each item template's cell.
* This dimension is used to help determine how many cells should
* be created when initialized, and to help calculate the height of
* the scrollable area. This value can use either `px` or `%` units.
* Note that the actual rendered size of each cell comes from the
* app's CSS, whereas this approximation is used to help calculate
* initial dimensions before the item has been rendered. Default is
* `100%`.
*/
@Input() approxItemWidth: string = '100%';
/**
* @input {string} It is important to provide this
* if virtual item height will be significantly larger than the default
* The approximate height of each virtual item template's cell.
* This dimension is used to help determine how many cells should
* be created when initialized, and to help calculate the height of
* the scrollable area. This height value can only use `px` units.
* Note that the actual rendered size of each cell comes from the
* app's CSS, whereas this approximation is used to help calculate
* initial dimensions before the item has been rendered. Default is
* `40px`.
*/
@Input() approxItemHeight: string;
/**
* @input {string} The approximate width of each header template's cell.
* This dimension is used to help determine how many cells should
* be created when initialized, and to help calculate the height of
* the scrollable area. This value can use either `px` or `%` units.
* Note that the actual rendered size of each cell comes from the
* app's CSS, whereas this approximation is used to help calculate
* initial dimensions. Default is `100%`.
*/
@Input() approxHeaderWidth: string = '100%';
/**
* @input {string} The approximate height of each header template's cell.
* This dimension is used to help determine how many cells should
* be created when initialized, and to help calculate the height of
* the scrollable area. This height value can only use `px` units.
* Note that the actual rendered size of each cell comes from the
* app's CSS, whereas this approximation is used to help calculate
* initial dimensions before the item has been rendered. Default is `40px`.
*/
@Input() approxHeaderHeight: string = '40px';
/**
* @input {string} The approximate width of each footer template's cell.
* This dimension is used to help determine how many cells should
* be created when initialized, and to help calculate the height of
* the scrollable area. This value can use either `px` or `%` units.
* Note that the actual rendered size of each cell comes from the
* app's CSS, whereas this approximation is used to help calculate
* initial dimensions before the item has been rendered. Default is `100%`.
*/
@Input() approxFooterWidth: string = '100%';
/**
* @input {string} The approximate height of each footer template's cell.
* This dimension is used to help determine how many cells should
* be created when initialized, and to help calculate the height of
* the scrollable area. This height value can only use `px` units.
* Note that the actual rendered size of each cell comes from the
* app's CSS, whereas this approximation is used to help calculate
* initial dimensions before the item has been rendered. Default is `40px`.
*/
@Input() approxFooterHeight: string = '40px';
/**
* @input {function} Section headers and the data used within its given
* template can be dynamically created by passing a function to `headerFn`.
* For example, a large list of contacts usually has dividers between each
* letter in the alphabet. App's can provide their own custom `headerFn`
* which is called with each record within the dataset. The logic within
* the header function can decide if the header template should be used,
* and what data to give to the header template. The function must return
* `null` if a header cell shouldn't be created.
*/
@Input() set headerFn(val: Function) {
if (isFunction(val)) {
this._hdrFn = val.bind((this._ctrl._cmp) || this);
}
}
/**
* @input {function} Section footers and the data used within its given
* template can be dynamically created by passing a function to `footerFn`.
* The logic within the footer function can decide if the footer template
* should be used, and what data to give to the footer template. The function
* must return `null` if a footer cell shouldn't be created.
*/
@Input() set footerFn(val: Function) {
if (isFunction(val)) {
this._ftrFn = val.bind((this._ctrl._cmp) || this);
}
}
/**
* @input {function} Same as `ngForTrackBy` which can be used on `ngFor`.
*/
@Input() virtualTrackBy: TrackByFn;
constructor(
private _iterableDiffers: IterableDiffers,
private _elementRef: ElementRef,
private _renderer: Renderer,
private _zone: NgZone,
private _cd: ChangeDetectorRef,
private _content: Content,
private _plt: Platform,
private _ctrl: ViewController,
private _config: Config,
private _dom: DomController) {
// hide the virtual scroll element with opacity so we don't
// see jank as it loads up, but we're still able to read
// dimensions because it's still rendered and only opacity hidden
this._renderer.setElementClass(_elementRef.nativeElement, 'virtual-loading', true);
// wait for the content to be rendered and has readable dimensions
_ctrl.readReady.subscribe(() => {
this._init = true;
if (this._hasChanges()) {
this.readUpdate();
// wait for the content to be writable
var subscription = _ctrl.writeReady.subscribe(() => {
subscription.unsubscribe();
this.writeUpdate();
});
}
this._listeners();
});
}
/**
* @private
*/
ngDoCheck() {
if (this._init && this._hasChanges()) {
// only continue if we've already initialized
// and if there actually are changes
this.readUpdate();
this.writeUpdate();
}
}
readUpdate() {
console.debug(`virtual-scroll, readUpdate`);
// reset everything
this._cells.length = 0;
this._nodes.length = 0;
this._itmTmp.viewContainer.clear();
// ******** DOM READ ****************
calcDimensions(this._data, this._elementRef.nativeElement,
this.approxItemWidth, this.approxItemHeight,
this.approxHeaderWidth, this.approxHeaderHeight,
this.approxFooterWidth, this.approxFooterHeight,
this.bufferRatio);
}
writeUpdate() {
console.debug(`virtual-scroll, writeUpdate`);
processRecords(this._data.renderHeight,
this._records,
this._cells,
this._hdrFn,
this._ftrFn,
this._data);
// ******** DOM WRITE ****************
this.renderVirtual();
}
private _hasChanges() {
return (isPresent(this._records) && isPresent(this._differ) && isPresent(this._differ.diff(this._records)));
}
/**
* @private
* DOM WRITE
*/
renderVirtual() {
const nodes = this._nodes;
const cells = this._cells;
const data = this._data;
const records = this._records;
// initialize nodes with the correct cell data
data.topCell = 0;
data.bottomCell = (cells.length - 1);
populateNodeData(0, data.bottomCell,
data.viewWidth, true,
cells, records, nodes,
this._itmTmp.viewContainer,
this._itmTmp.templateRef,
this._hdrTmp && this._hdrTmp.templateRef,
this._ftrTmp && this._ftrTmp.templateRef, true);
// ******** DOM WRITE ****************
this._cd.detectChanges();
// at this point, this fn was called from within another
// requestAnimationFrame, so the next dom reads/writes within the next frame
// wait a frame before trying to read and calculate the dimensions
this._dom.read(() => {
// ******** DOM READ ****************
initReadNodes(this._plt, nodes, cells, data);
});
this._dom.write(() => {
const ele = this._elementRef.nativeElement;
const recordsLength = records.length;
const renderer = this._renderer;
// update the bound context for each node
updateNodeContext(nodes, cells, data);
// ******** DOM WRITE ****************
for (var i = 0; i < nodes.length; i++) {
(nodes[i].view).detectChanges();
}
if (!this._lastEle) {
// add an element at the end so :last-child css doesn't get messed up
// ******** DOM WRITE ****************
var lastEle: HTMLElement = renderer.createElement(ele, 'div');
lastEle.className = 'virtual-last';
this._lastEle = true;
}
// ******** DOM WRITE ****************
renderer.setElementClass(ele, 'virtual-scroll', true);
// ******** DOM WRITE ****************
renderer.setElementClass(ele, 'virtual-loading', false);
// ******** DOM WRITE ****************
writeToNodes(this._plt, nodes, cells, recordsLength);
// ******** DOM WRITE ****************
this._setHeight(
estimateHeight(recordsLength, cells[cells.length - 1], this._vHeight, 0.25)
);
this._content.imgsUpdate();
});
}
/**
* @private
*/
scrollUpdate(ev: ScrollEvent) {
// there is a queue system so that we can
// spread out the work over multiple frames
const data = this._data;
const cells = this._cells;
const nodes = this._nodes;
// set the scroll top from the scroll event
data.scrollTop = ev.scrollTop;
if (this._queue === SCROLL_QUEUE_DOM_WRITE) {
// there are DOM writes we need to take care of in this frame
this._dom.write(() => {
const recordsLength = this._records.length;
// ******** DOM WRITE ****************
writeToNodes(this._plt, nodes, cells, recordsLength);
// ******** DOM WRITE ****************
this._setHeight(
estimateHeight(recordsLength, cells[cells.length - 1], this._vHeight, 0.25)
);
// we're done here, good work
this._queue = SCROLL_QUEUE_NO_CHANGES;
});
} else if (this._queue === SCROLL_QUEUE_CHANGE_DETECTION) {
// we need to do some change detection in this frame
this._dom.write(() => {
// we've got work painting do, let's throw it in the
// domWrite callback so everyone plays nice
// ******** DOM WRITE ****************
for (var i = 0; i < nodes.length; i++) {
if (nodes[i].hasChanges) {
(nodes[i].view).detectChanges();
}
}
// on the next frame we need write to the dom nodes manually
this._queue = SCROLL_QUEUE_DOM_WRITE;
});
} else {
// no dom writes or change detection to take care of
// let's see if we've scroll far enough to require another check
data.scrollDiff = (data.scrollTop - this._lastCheck);
if (Math.abs(data.scrollDiff) > SCROLL_DIFFERENCE_MINIMUM) {
// don't bother updating if the scrollTop hasn't changed much
this._lastCheck = data.scrollTop;
if (data.scrollDiff > 0) {
// load data we may not have processed yet
var stopAtHeight = (data.scrollTop + data.renderHeight);
processRecords(stopAtHeight, this._records, cells,
this._hdrFn, this._ftrFn, data);
}
// ******** DOM READ ****************
updateDimensions(this._plt, nodes, cells, data, false);
adjustRendered(cells, data);
var hasChanges = populateNodeData(data.topCell, data.bottomCell,
data.viewWidth, data.scrollDiff > 0,
cells, this._records, nodes,
this._itmTmp.viewContainer,
this._itmTmp.templateRef,
this._hdrTmp && this._hdrTmp.templateRef,
this._ftrTmp && this._ftrTmp.templateRef, false);
if (hasChanges) {
// queue making updates in the next frame
this._queue = SCROLL_QUEUE_CHANGE_DETECTION;
// update the bound context for each node
updateNodeContext(nodes, cells, data);
}
}
}
}
/**
* @private
* DOM WRITE
*/
scrollEnd(ev: ScrollEvent) {
const nodes = this._nodes;
const cells = this._cells;
const data = this._data;
// ******** DOM READ ****************
updateDimensions(this._plt, nodes, cells, data, false);
adjustRendered(cells, data);
// ******** DOM READS ABOVE / DOM WRITES BELOW ****************
this._dom.write(() => {
const recordsLength = this._records.length;
// update the bound context for each node
updateNodeContext(nodes, cells, data);
// ******** DOM WRITE ****************
for (var i = 0; i < nodes.length; i++) {
(nodes[i].view).detectChanges();
}
// ******** DOM WRITE ****************
writeToNodes(this._plt, nodes, cells, recordsLength);
// ******** DOM WRITE ****************
this._setHeight(
estimateHeight(recordsLength, cells[cells.length - 1], this._vHeight, 0.05)
);
this._queue = SCROLL_QUEUE_NO_CHANGES;
});
}
/**
* NO DOM
*/
private _listeners() {
if (!this._scrollSub) {
if (this._config.getBoolean('virtualScrollEventAssist')) {
// use JS scrolling for iOS UIWebView
// goal is to completely remove this when iOS
// fully supports scroll events
// listen to JS scroll events
this._content.enableJsScroll();
}
this._scrollSub = this._content.ionScroll.subscribe((ev: ScrollEvent) => {
this.scrollUpdate(ev);
});
this._scrollEndSub = this._content.ionScrollEnd.subscribe((ev: ScrollEvent) => {
this.scrollEnd(ev);
});
}
}
/**
* DOM WRITE
*/
private _setHeight(newVirtualHeight: number) {
if (newVirtualHeight !== this._vHeight) {
// ******** DOM WRITE ****************
this._renderer.setElementStyle(this._elementRef.nativeElement, 'height', newVirtualHeight > 0 ? newVirtualHeight + 'px' : '');
this._vHeight = newVirtualHeight;
console.debug('VirtualScroll, height', newVirtualHeight);
}
}
/**
* @private
*/
ngAfterContentInit() {
if (!this._itmTmp) {
throw 'virtualItem required within virtualScroll';
}
if (!this.approxItemHeight) {
this.approxItemHeight = '40px';
console.warn('Virtual Scroll: Please provide an "approxItemHeight" input to ensure proper virtual scroll rendering');
}
}
/**
* @private
*/
ngOnDestroy() {
this._scrollSub && this._scrollSub.unsubscribe();
this._scrollEndSub && this._scrollEndSub.unsubscribe();
}
}
const SCROLL_DIFFERENCE_MINIMUM = 40;
const SCROLL_QUEUE_NO_CHANGES = 1;
const SCROLL_QUEUE_CHANGE_DETECTION = 2;
const SCROLL_QUEUE_DOM_WRITE = 3;
*
* {% raw %} {{ item }}{% endraw %}
*
*
*
*