ReactNativeEventEmitter.js

/**
 * Copyright (c) 2015-present, Facebook, Inc.
 * All rights reserved.
 *
 * This source code is licensed under the BSD-style license found in the
 * LICENSE file in the root directory of this source tree. An additional grant
 * of patent rights can be found in the PATENTS file in the same directory.
 *
 * @providesModule ReactNativeEventEmitter
 * @flow
 */
'use strict';

var EventPluginHub = require('EventPluginHub');
var EventPluginRegistry = require('EventPluginRegistry');
var ReactEventEmitterMixin = require('ReactEventEmitterMixin');
var ReactNativeComponentTree = require('ReactNativeComponentTree');
var ReactNativeTagHandles = require('ReactNativeTagHandles');
var ReactGenericBatching = require('ReactGenericBatching');

if (__DEV__) {
  var warning = require('fbjs/lib/warning');
}

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

// Shared default empty native event - conserve memory.
var EMPTY_NATIVE_EVENT = {};

/**
 * 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.
 */
var touchSubsequence = function(touches, indices) {
  var ret = [];
  for (var 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.
 */
var removeTouchesAtIndices = function(
  touches: Array<Object>,
  indices: Array<number>,
): Array<Object> {
  var rippedOut = [];
  // use an unsafe downcast to alias to nullable elements,
  // so we can delete and then compact.
  var temp: Array<?Object> = (touches: Array<any>);
  for (var i = 0; i < indices.length; i++) {
    var index = indices[i];
    rippedOut.push(touches[index]);
    temp[index] = null;
  }
  var fillAt = 0;
  for (var j = 0; j < temp.length; j++) {
    var cur = temp[j];
    if (cur !== null) {
      temp[fillAt++] = cur;
    }
  }
  temp.length = fillAt;
  return rippedOut;
};

var ReactNativeEventEmitter = {
  ...ReactEventEmitterMixin,

  registrationNames: EventPluginRegistry.registrationNameModules,

  getListener: EventPluginHub.getListener,

  /**
   * 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.
   */
  _receiveRootNodeIDEvent: function(
    rootNodeID: number,
    topLevelType: string,
    nativeEventParam: ?Object,
  ) {
    var nativeEvent = nativeEventParam || EMPTY_NATIVE_EVENT;
    var inst = ReactNativeComponentTree.getInstanceFromNode(rootNodeID);
    ReactGenericBatching.batchedUpdates(function() {
      ReactNativeEventEmitter.handleTopLevel(
        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.
   */
  receiveEvent: function(
    rootNodeID: number,
    topLevelType: string,
    nativeEventParam: Object,
  ) {
    ReactNativeEventEmitter._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.
   */
  receiveTouches: function(
    eventTopLevelType: string,
    touches: Array<Object>,
    changedIndices: Array<number>,
  ) {
    var changedTouches = eventTopLevelType === 'topTouchEnd' ||
      eventTopLevelType === 'topTouchCancel'
      ? removeTouchesAtIndices(touches, changedIndices)
      : touchSubsequence(touches, changedIndices);

    for (var jj = 0; jj < changedTouches.length; jj++) {
      var 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;
      var nativeEvent = touch;
      var rootNodeID = null;
      var target = nativeEvent.target;
      if (target !== null && target !== undefined) {
        if (target < ReactNativeTagHandles.tagsStartAt) {
          if (__DEV__) {
            warning(
              false,
              'A view is reporting that a touch occurred on tag zero.',
            );
          }
        } else {
          rootNodeID = target;
        }
      }
      ReactNativeEventEmitter._receiveRootNodeIDEvent(
        rootNodeID,
        eventTopLevelType,
        nativeEvent,
      );
    }
  },
};

module.exports = ReactNativeEventEmitter;