react-native-gesture-handler/lib/module/web/tools/ScrollEventManager.js

Declarative API exposing native platform touch and gesture system to React Native

"use strict";

import { PointerType } from '../../PointerType';
import { EventTypes } from '../interfaces';
import EventManager from './EventManager';
export default class ScrollEventManager extends EventManager {
  scrollCallback = event => {
    this.onScroll(this.mapEvent(event));
  };
  registerListeners() {
    this.view.addEventListener('scroll', this.scrollCallback, {
      passive: true
    });
  }
  unregisterListeners() {
    this.view.removeEventListener('scroll', this.scrollCallback);
  }
  mapEvent(event) {
    // Synthesize a pointer glued to the scrolled content - deltas between
    // events equal the scrolled distance. getBoundingClientRect would only
    // add a constant offset at the cost of a layout read on every event.
    return {
      x: -this.view.scrollLeft,
      y: -this.view.scrollTop,
      offsetX: -this.view.scrollLeft,
      offsetY: -this.view.scrollTop,
      pointerId: -1,
      eventType: EventTypes.MOVE,
      pointerType: PointerType.OTHER,
      time: event.timeStamp
    };
  }
}
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