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fix(template): keep scroll offset when using keepScrolledIndexOnPrepend (#1857) #1859

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fix(template): keep scroll offset when using keepScrolledIndexOnPrepend (#1857) #1859

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31 changes: 23 additions & 8 deletions ...erimental/virtual-scrolling/src/lib/scroll-strategies/autosize-virtual-scroll-strategy.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -234,6 +234,7 @@ export class AutoSizeVirtualScrollStrategy<
private scrollToTrigger$ = new Subject<{
scrollTop: number;
behavior?: ScrollBehavior;
offset: number;
}>();
/** @internal */
private _scrolledIndex = 0;
Expand All @@ -252,6 +253,7 @@ export class AutoSizeVirtualScrollStrategy<
* @internal
* */
private _scrollToIndex: number | null = null;
private _scrollToOffset: number | null = null;

/** @internal */
private containerSize = 0;
Expand Down Expand Up @@ -355,25 +357,34 @@ export class AutoSizeVirtualScrollStrategy<
this.detached$.next();
}

scrollToIndex(index: number, behavior?: ScrollBehavior): void {
scrollToIndex(
index: number,
behavior?: ScrollBehavior,
offset: number = 0,
): void {
const _index = Math.min(
Math.max(index, 0),
Math.max(0, this.contentLength - 1),
);
if (_index !== this.scrolledIndex) {
const scrollTop = this.calcInitialPosition(_index);
this._scrollToIndex = _index;
this.scrollToTrigger$.next({ scrollTop, behavior });
this._scrollToOffset = offset;
this.scrollToTrigger$.next({ scrollTop, behavior, offset });
}
}

private scrollTo(scrollTo: number, behavior?: ScrollBehavior): void {
private scrollTo(
scrollTo: number,
behavior?: ScrollBehavior,
offset: number = 0,
): void {
this.waitForScroll =
scrollTo !== this.scrollTop && this.contentSize > this.containerSize;
if (this.waitForScroll) {
this.isStable$.next(false);
}
this.viewport!.scrollTo(this.viewportOffset + scrollTo, behavior);
this.viewport!.scrollTo(this.viewportOffset + scrollTo + offset, behavior);
}

/**
Expand Down Expand Up @@ -486,7 +497,11 @@ export class AutoSizeVirtualScrollStrategy<
keepScrolledIndexOnPrepend &&
this.anchorItem.index !== anchorItemIndex
) {
this.scrollToIndex(anchorItemIndex);
this.scrollToIndex(
anchorItemIndex,
undefined,
this.anchorItem.offset,
);
} else if (dataLength === 0) {
this.anchorItem = {
index: 0,
Expand Down Expand Up @@ -708,7 +723,7 @@ export class AutoSizeVirtualScrollStrategy<
virtualItem.position = position;
}
if (this._scrollToIndex === itemIndex) {
scrollToAnchorPosition = position;
scrollToAnchorPosition = position + this._scrollToOffset;
}
position += size;
// immediately activate the ResizeObserver after initial positioning
Expand Down Expand Up @@ -825,8 +840,8 @@ export class AutoSizeVirtualScrollStrategy<
),
this.until$(),
)
.subscribe(({ scrollTop, behavior }) => {
this.scrollTo(scrollTop, behavior);
.subscribe(({ scrollTop, behavior, offset }) => {
this.scrollTo(scrollTop, behavior, offset);
});
}
/** @internal */
Expand Down
10 changes: 7 additions & 3 deletions ...ental/virtual-scrolling/src/lib/scroll-strategies/dynamic-size-virtual-scroll-strategy.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -273,13 +273,17 @@ export class DynamicSizeVirtualScrollStrategy<
this.detached$.next();
}

scrollToIndex(index: number, behavior?: ScrollBehavior): void {
scrollToIndex(
index: number,
behavior?: ScrollBehavior,
offset: number = 0,
): void {
const _index = Math.min(Math.max(index, 0), this.contentLength - 1);
let scrollTo = 0;
for (let i = 0; i < _index; i++) {
scrollTo += this._virtualItems[i].size;
}
this.scrollTo(scrollTo, behavior);
this.scrollTo(scrollTo + offset, behavior);
}

private scrollTo(scrollTo: number, behavior?: ScrollBehavior): void {
Expand Down Expand Up @@ -394,7 +398,7 @@ export class DynamicSizeVirtualScrollStrategy<
valueCache = {};
valueArray.forEach((v, i) => (valueCache[trackBy(i, v)] = v));
if (scrollTo !== this.scrolledIndex) {
this.scrollToIndex(scrollTo);
this.scrollToIndex(scrollTo, undefined, this.anchorItem.offset);
}
});
}
Expand Down
14 changes: 11 additions & 3 deletions ...imental/virtual-scrolling/src/lib/scroll-strategies/fixed-size-virtual-scroll-strategy.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -265,7 +265,11 @@ export class FixedSizeVirtualScrollStrategy<
valueCache = {};
valueArray.forEach((v, i) => (valueCache[trackBy(i, v)] = v));
if (scrollTo !== this.scrolledIndex) {
this.scrollToIndex(scrollTo);
this.scrollToIndex(
scrollTo,
undefined,
this.scrollTop % this._itemSize,
);
}
});
const dataLengthChanged$ = valueArray$.pipe(
Expand Down Expand Up @@ -359,9 +363,13 @@ export class FixedSizeVirtualScrollStrategy<
.subscribe((range) => (this.renderedRange = range));
}

scrollToIndex(index: number, behavior?: ScrollBehavior): void {
scrollToIndex(
index: number,
behavior?: ScrollBehavior,
offset: number = 0,
): void {
const scrollTop = this.itemSize * index;
this.viewport!.scrollTo(this.viewportOffset + scrollTop, behavior);
this.viewport!.scrollTo(this.viewportOffset + scrollTop + offset, behavior);
}

private untilDetached$<A>(): MonoTypeOperatorFunction<A> {
Expand Down