react/packages/react-native-renderer/src/ReactNativeEventEmitter.js

/**
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow
 */

import {getListener, runExtractedEventsInBatch} from 'events/EventPluginHub';
import {registrationNameModules} from 'events/EventPluginRegistry';
import {batchedUpdates} from 'events/ReactGenericBatching';
import warningWithoutStack from 'shared/warningWithoutStack';

import {getInstanceFromNode} from './ReactNativeComponentTree';

import type {AnyNativeEvent} from 'events/PluginModuleType';
import type {TopLevelType} from 'events/TopLevelEventTypes';

export {getListener, registrationNameModules as registrationNames};

/**
 * Version of `ReactBrowserEventEmitter` that works on the receiving side of a
 * serialized worker boundary.
 */

// Shared default empty native event - conserve memory.
const EMPTY_NATIVE_EVENT = (({}: any): AnyNativeEvent);

/**
 * Selects a subsequence of `Touch`es, without destroying `touches`.
 *
 * @param {Array<Touch>} touches Deserialized touch objects.
 * @param {Array<number>} indices Indices by which to pull subsequence.
 * @return {Array<Touch>} Subsequence of touch objects.
 */
const touchSubsequence = function(touches, indices) {
  const ret = [];
  for (let i = 0; i < indices.length; i++) {
    ret.push(touches[indices[i]]);
  }
  return ret;
};

/**
 * TODO: Pool all of this.
 *
 * Destroys `touches` by removing touch objects at indices `indices`. This is
 * to maintain compatibility with W3C touch "end" events, where the active
 * touches don't include the set that has just been "ended".
 *
 * @param {Array<Touch>} touches Deserialized touch objects.
 * @param {Array<number>} indices Indices to remove from `touches`.
 * @return {Array<Touch>} Subsequence of removed touch objects.
 */
const removeTouchesAtIndices = function(
  touches: Array<Object>,
  indices: Array<number>,
): Array<Object> {
  const rippedOut = [];
  // use an unsafe downcast to alias to nullable elements,
  // so we can delete and then compact.
  const temp: Array<?Object> = (touches: Array<any>);
  for (let i = 0; i < indices.length; i++) {
    const index = indices[i];
    rippedOut.push(touches[index]);
    temp[index] = null;
  }
  let fillAt = 0;
  for (let j = 0; j < temp.length; j++) {
    const cur = temp[j];
    if (cur !== null) {
      temp[fillAt++] = cur;
    }
  }
  temp.length = fillAt;
  return rippedOut;
};

/**
 * Internal version of `receiveEvent` in terms of normalized (non-tag)
 * `rootNodeID`.
 *
 * @see receiveEvent.
 *
 * @param {rootNodeID} rootNodeID React root node ID that event occurred on.
 * @param {TopLevelType} topLevelType Top level type of event.
 * @param {?object} nativeEventParam Object passed from native.
 */
function _receiveRootNodeIDEvent(
  rootNodeID: number,
  topLevelType: TopLevelType,
  nativeEventParam: ?AnyNativeEvent,
) {
  const nativeEvent = nativeEventParam || EMPTY_NATIVE_EVENT;
  const inst = getInstanceFromNode(rootNodeID);
  batchedUpdates(function() {
    runExtractedEventsInBatch(
      topLevelType,
      inst,
      nativeEvent,
      nativeEvent.target,
    );
  });
  // React Native doesn't use ReactControlledComponent but if it did, here's
  // where it would do it.
}

/**
 * Publicly exposed method on module for native objc to invoke when a top
 * level event is extracted.
 * @param {rootNodeID} rootNodeID React root node ID that event occurred on.
 * @param {TopLevelType} topLevelType Top level type of event.
 * @param {object} nativeEventParam Object passed from native.
 */
export function receiveEvent(
  rootNodeID: number,
  topLevelType: TopLevelType,
  nativeEventParam: AnyNativeEvent,
) {
  _receiveRootNodeIDEvent(rootNodeID, topLevelType, nativeEventParam);
}

/**
 * Simple multi-wrapper around `receiveEvent` that is intended to receive an
 * efficient representation of `Touch` objects, and other information that
 * can be used to construct W3C compliant `Event` and `Touch` lists.
 *
 * This may create dispatch behavior that differs than web touch handling. We
 * loop through each of the changed touches and receive it as a single event.
 * So two `touchStart`/`touchMove`s that occur simultaneously are received as
 * two separate touch event dispatches - when they arguably should be one.
 *
 * This implementation reuses the `Touch` objects themselves as the `Event`s
 * since we dispatch an event for each touch (though that might not be spec
 * compliant). The main purpose of reusing them is to save allocations.
 *
 * TODO: Dispatch multiple changed touches in one event. The bubble path
 * could be the first common ancestor of all the `changedTouches`.
 *
 * One difference between this behavior and W3C spec: cancelled touches will
 * not appear in `.touches`, or in any future `.touches`, though they may
 * still be "actively touching the surface".
 *
 * Web desktop polyfills only need to construct a fake touch event with
 * identifier 0, also abandoning traditional click handlers.
 */
export function receiveTouches(
  eventTopLevelType: TopLevelType,
  touches: Array<Object>,
  changedIndices: Array<number>,
) {
  const changedTouches =
    eventTopLevelType === 'topTouchEnd' ||
    eventTopLevelType === 'topTouchCancel'
      ? removeTouchesAtIndices(touches, changedIndices)
      : touchSubsequence(touches, changedIndices);

  for (let jj = 0; jj < changedTouches.length; jj++) {
    const touch = changedTouches[jj];
    // Touch objects can fulfill the role of `DOM` `Event` objects if we set
    // the `changedTouches`/`touches`. This saves allocations.
    touch.changedTouches = changedTouches;
    touch.touches = touches;
    const nativeEvent = touch;
    let rootNodeID = null;
    const target = nativeEvent.target;
    if (target !== null && target !== undefined) {
      if (target < 1) {
        if (__DEV__) {
          warningWithoutStack(
            false,
            'A view is reporting that a touch occurred on tag zero.',
          );
        }
      } else {
        rootNodeID = target;
      }
    }
    // $FlowFixMe Shouldn't we *not* call it if rootNodeID is null?
    _receiveRootNodeIDEvent(rootNodeID, eventTopLevelType, nativeEvent);
  }
}