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feat(virtual-scroll): adds headerHeight and footerHeight (#18851)

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Currently, if you have an ion-virtual-scroll with a list of items and a search bar for filtering them, when you change the list of items, the items disappear until rendered again, causing a flicker. This could be solved for the items using the itemHeight function to provide the exact height size and bypass some calculations and be more performant etc.

However, if you had a header or footer, they would still flicker. This commit adds two more optional functions named headerHeight and footerHeight that return the exact size of the header and footer respectively and resolve the flicker.
This commit is contained in:
Stefanos Anagnostou
2019-07-24 19:29:16 +03:00
committed by Manu MA
parent c91819c94f
commit 00891119f7
8 changed files with 72 additions and 16 deletions
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20
angular/src/directives/virtual-scroll/virtual-scroll.ts
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@ -1,5 +1,5 @@
import { ChangeDetectionStrategy, Component, ContentChild, ElementRef, EmbeddedViewRef, IterableDiffer, IterableDiffers, NgZone, SimpleChanges, TrackByFunction } from '@angular/core';
import { Cell, CellType, HeaderFn, ItemHeightFn } from '@ionic/core';
import { Cell, CellType, FooterHeightFn, HeaderFn, HeaderHeightFn, ItemHeightFn } from '@ionic/core';
import { proxyInputs, proxyMethods } from '../proxies-utils';
@ -75,7 +75,7 @@ export declare interface IonVirtualScroll {
/**
* An optional function that maps each item within their height.
* When this function is provides, heavy optimizations and fast path can be taked by
* When this function is provided, heavy optimizations and fast path can be taked by
* `ion-virtual-scroll` leading to massive performance improvements.
*
* This function allows to skip all DOM reads, which can be Doing so leads
@ -83,6 +83,16 @@ export declare interface IonVirtualScroll {
*/
itemHeight?: ItemHeightFn;
/**
* An optional function that maps each item header within their height.
*/
headerHeight?: HeaderHeightFn;
/**
* An optional function that maps each item footer within their height.
*/
footerHeight?: FooterHeightFn;
/**
* Same as `ngForTrackBy` which can be used on `ngFor`.
*/
@ -114,6 +124,8 @@ export declare interface IonVirtualScroll {
'footerFn',
'items',
'itemHeight',
'headerHeight',
'footerHeight',
'trackBy'
]
})
@ -211,7 +223,9 @@ proxyInputs(IonVirtualScroll, [
'headerFn',
'footerFn',
'items',
'itemHeight'
'itemHeight',
'headerHeight',
'footerHeight'
]);
proxyMethods(IonVirtualScroll, [