@shopify/flash-list
Version:
FlashList is a more performant FlatList replacement
60 lines • 2.51 kB
JavaScript
/**
* This method can be used to trigger scroll events that can be forwarded to an element. Anything that implements scrollable can leverage this.
* @param scroll The scrollable element
* @param fromX The x offset to start from
* @param fromY The y offset to start from
* @param toX the x offset to end scroll at
* @param toY the y offset to end scroll at
* @param speedMultiplier the speed multiplier to use
* @param cancellable can be used to cancel the scroll
* @returns Promise that resolves when the scroll is complete
*/
export function autoScroll(scroll, fromX, fromY, toX, toY, speedMultiplier = 1, cancellable = new Cancellable()) {
return new Promise((resolve) => {
scroll(fromX, fromY, false);
// Very fast scrolls on Android/iOS typically move content 7px every millisecond.
const incrementPerMs = 7 * speedMultiplier;
const directionMultiplierX = toX > fromX ? 1 : -1;
const directionMultiplierY = toY > fromY ? 1 : -1;
const comparatorX = toX > fromX ? Math.min : Math.max;
const comparatorY = toY > fromY ? Math.min : Math.max;
let startTime = Date.now();
let startX = fromX;
let startY = fromY;
// Computes the number of pixels to scroll in the given time
// Also invokes the scrollable to update the scroll position
const animationLoop = () => {
requestAnimationFrame(() => {
if (cancellable.isCancelled()) {
resolve(false);
return;
}
const currentTime = Date.now();
const timeElapsed = currentTime - startTime;
const distanceToCover = incrementPerMs * timeElapsed;
startX += distanceToCover * directionMultiplierX;
startY += distanceToCover * directionMultiplierY;
scroll(comparatorX(toX, startX), comparatorY(toY, startY), false);
startTime = currentTime;
if (comparatorX(toX, startX) !== toX ||
comparatorY(toY, startY) !== toY) {
return animationLoop();
}
resolve(true);
});
};
animationLoop();
});
}
export class Cancellable {
constructor() {
this._isCancelled = false;
}
cancel() {
this._isCancelled = true;
}
isCancelled() {
return this._isCancelled;
}
}
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