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Improve heuristic that triggers onStartReached #44287

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Improve heuristic that triggers onStartReached #44287

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d277ca9
Improve heuristic that triggers onStartReached
janicduplessis Apr 26, 2024
546df34
Update VirtualizedList.js
janicduplessis May 6, 2024
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11 changes: 5 additions & 6 deletions packages/virtualized-lists/Lists/VirtualizedList.js
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Original file line number Diff line number Diff line change
Expand Up @@ -1219,7 +1219,7 @@ class VirtualizedList extends StateSafePureComponent<Props, State> {
zoomScale: 1,
};
_scrollRef: ?React.ElementRef<any> = null;
_sentStartForContentLength = 0;
_sentStartForFirstVisibleItemKey: ?string = null;
_sentEndForContentLength = 0;
_updateCellsToRenderBatcher: Batchinator;
_viewabilityTuples: Array<ViewabilityHelperCallbackTuple> = [];
Expand Down Expand Up @@ -1546,22 +1546,21 @@ class VirtualizedList extends StateSafePureComponent<Props, State> {
}

// Next check if the user just scrolled within the start threshold
// and call onStartReached only once for a given content length,
// and only if onEndReached is not being executed
// and call onStartReached only once for a given first visible item
if (
onStartReached != null &&
this.state.cellsAroundViewport.first === 0 &&
isWithinStartThreshold &&
this._listMetrics.getContentLength() !== this._sentStartForContentLength
this.state.firstVisibleItemKey !== this._sentStartForFirstVisibleItemKey
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Comment above is now out of date it looks like

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Fixed, and only if onEndReached is not being executed that part was also out of date from a previous change.

) {
this._sentStartForContentLength = this._listMetrics.getContentLength();
this._sentStartForFirstVisibleItemKey = this.state.firstVisibleItemKey;
onStartReached({distanceFromStart});
}

// If the user scrolls away from the start or end and back again,
// cause onStartReached or onEndReached to be triggered again
if (!isWithinStartThreshold) {
this._sentStartForContentLength = 0;
this._sentStartForFirstVisibleItemKey = null;
}
if (!isWithinEndThreshold) {
this._sentEndForContentLength = 0;
Expand Down