react-native-gesture-handler/lib/module/handlers/gestures/gestureComposition.js

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

"use strict";

import { BaseGesture, Gesture } from './gesture';
function extendRelation(currentRelation, extendWith) {
  if (currentRelation === undefined) {
    return [...extendWith];
  } else {
    return [...currentRelation, ...extendWith];
  }
}
export class ComposedGesture extends Gesture {
  gestures = [];
  simultaneousGestures = [];
  requireGesturesToFail = [];
  constructor(...gestures) {
    super();
    this.gestures = gestures;
  }
  prepareSingleGesture(gesture, simultaneousGestures, requireGesturesToFail) {
    if (gesture instanceof BaseGesture) {
      const newConfig = {
        ...gesture.config
      };

      // No need to extend `blocksHandlers` here, because it's not changed in composition.
      // The same effect is achieved by reversing the order of 2 gestures in `Exclusive`
      newConfig.simultaneousWith = extendRelation(newConfig.simultaneousWith, simultaneousGestures);
      newConfig.requireToFail = extendRelation(newConfig.requireToFail, requireGesturesToFail);
      gesture.config = newConfig;
    } else if (gesture instanceof ComposedGesture) {
      gesture.simultaneousGestures = simultaneousGestures;
      gesture.requireGesturesToFail = requireGesturesToFail;
      gesture.prepare();
    }
  }
  prepare() {
    for (const gesture of this.gestures) {
      this.prepareSingleGesture(gesture, this.simultaneousGestures, this.requireGesturesToFail);
    }
  }
  initialize() {
    for (const gesture of this.gestures) {
      gesture.initialize();
    }
  }
  toGestureArray() {
    return this.gestures.flatMap(gesture => gesture.toGestureArray());
  }
}
export class SimultaneousGesture extends ComposedGesture {
  prepare() {
    // This piece of magic works something like this:
    // for every gesture in the array
    const simultaneousArrays = this.gestures.map(gesture =>
    // we take the array it's in
    this.gestures
    // and make a copy without it
    .filter(x => x !== gesture)
    // then we flatmap the result to get list of raw (not composed) gestures
    // this way we don't make the gestures simultaneous with themselves, which is
    // important when the gesture is `ExclusiveGesture` - we don't want to make
    // exclusive gestures simultaneous
    .flatMap(x => x.toGestureArray()));
    for (let i = 0; i < this.gestures.length; i++) {
      this.prepareSingleGesture(this.gestures[i], simultaneousArrays[i], this.requireGesturesToFail);
    }
  }
}
export class ExclusiveGesture extends ComposedGesture {
  prepare() {
    // Transforms the array of gestures into array of grouped raw (not composed) gestures
    // i.e. [gesture1, gesture2, ComposedGesture(gesture3, gesture4)] -> [[gesture1], [gesture2], [gesture3, gesture4]]
    const gestureArrays = this.gestures.map(gesture => gesture.toGestureArray());
    let requireToFail = [];
    for (let i = 0; i < this.gestures.length; i++) {
      this.prepareSingleGesture(this.gestures[i], this.simultaneousGestures, this.requireGesturesToFail.concat(requireToFail));

      // Every group gets to wait for all groups before it
      requireToFail = requireToFail.concat(gestureArrays[i]);
    }
  }
}
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