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Improve jump compensation immediately after prepending #276

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merged 1 commit into from
Dec 6, 2023
Merged

Improve jump compensation immediately after prepending #276

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23 changes: 17 additions & 6 deletions src/core/store.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -129,6 +129,7 @@ export const createVirtualStore = (
let pendingJump = 0;
let _flushedJump = 0;
let _scrollDirection: ScrollDirection = SCROLL_IDLE;
let _prepended = false;
let _isManualScrolling = false;
let _smoothScrollRange: ItemsRange | null = null;
let _prevRange: ItemsRange = [0, initialItemCount];
Expand Down Expand Up @@ -252,6 +253,9 @@ export const createVirtualStore = (
const updated = payload.filter(
([index, size]) => cache._sizes[index] !== size
);
const isJustPrepended = _prepended;
_prepended = false;

// Skip if all items are cached and not updated
if (!updated.length) {
break;
Expand All @@ -267,12 +271,18 @@ export const createVirtualStore = (
// Keep end to stick to the end
diff = calculateJump(cache, updated, true);
} else {
const [startIndex] = _prevRange;
// Keep start at mid
diff = calculateJump(
cache,
updated.filter(([index]) => index < startIndex)
);
if (isJustPrepended) {
// Keep distance from end immediately after prepending
// We can assume jumps occurred on the upper outside
diff = calculateJump(cache, updated);
} else {
// Keep start at mid
const [startIndex] = _prevRange;
diff = calculateJump(
cache,
updated.filter(([index]) => index < startIndex)
);
}
}

if (diff) {
Expand Down Expand Up @@ -326,6 +336,7 @@ export const createVirtualStore = (
);
applyJump(isRemove ? -min(shift, distanceToEnd) : shift);

_prepended = !isRemove;
mutated = UPDATE_SCROLL_STATE;
} else {
updateCacheLength(cache as Writeable<Cache>, payload[0]);
Expand Down
15 changes: 0 additions & 15 deletions stories/advanced/Feed.stories.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -62,16 +62,10 @@ export const Default: StoryObj = {
const createItems = (num: number) => range(num, createItem);

const [shifting, setShifting] = useState(false);
const [startFetching, setStartFetching] = useState(false);
const [endFetching, setEndFetching] = useState(false);
const fetchItems = async (isStart: boolean = false) => {
setShifting(isStart);

const setFetching = isStart ? setStartFetching : setEndFetching;

setFetching(true);
await delay(1000);
setFetching(false);
};

const ref = useRef<VListHandle>(null);
Expand Down Expand Up @@ -128,16 +122,7 @@ export const Default: StoryObj = {
}
}}
>
{/* // TODO support the case when spinner is at index 0
<Spinner
key="head"
style={startFetching ? undefined : { visibility: "hidden" }}
/> */}
{elements}
<Spinner
key="foot"
style={endFetching ? undefined : { visibility: "hidden" }}
/>
</VList>
);
},
Expand Down
3 changes: 1 addition & 2 deletions stories/basics/VList.stories.tsx
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Original file line number Diff line number Diff line change
Expand Up @@ -623,11 +623,10 @@ export const BiDirectionalInfiniteScrolling: StoryObj = {
}
}}
>
{/* // TODO support the case when spinner is at index 0
<Spinner
key="head"
style={startFetching ? undefined : { visibility: "hidden" }}
/> */}
/>
{items}
<Spinner
key="foot"
Expand Down
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