react-native/Libraries/Renderer/src/renderers/native/ReactNativeTagHandles.js

A framework for building native apps using React

/**
 * 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 ReactNativeTagHandles
 * @flow
 */
'use strict';

var invariant = require('fbjs/lib/invariant');

/**
 * Keeps track of allocating and associating native "tags" which are numeric,
 * unique view IDs. All the native tags are negative numbers, to avoid
 * collisions, but in the JS we keep track of them as positive integers to store
 * them effectively in Arrays. So we must refer to them as "inverses" of the
 * native tags (that are * normally negative).
 *
 * It *must* be the case that every `rootNodeID` always maps to the exact same
 * `tag` forever. The easiest way to accomplish this is to never delete
 * anything from this table.
 * Why: Because `dangerouslyReplaceNodeWithMarkupByID` relies on being able to
 * unmount a component with a `rootNodeID`, then mount a new one in its place,
 */
var INITIAL_TAG_COUNT = 1;
var ReactNativeTagHandles = {
  tagsStartAt: INITIAL_TAG_COUNT,
  tagCount: INITIAL_TAG_COUNT,

  allocateTag: function(): number {
    // Skip over root IDs as those are reserved for native
    while (this.reactTagIsNativeTopRootID(ReactNativeTagHandles.tagCount)) {
      ReactNativeTagHandles.tagCount++;
    }
    var tag = ReactNativeTagHandles.tagCount;
    ReactNativeTagHandles.tagCount++;
    return tag;
  },

  assertRootTag: function(tag: number): void {
    invariant(
      this.reactTagIsNativeTopRootID(tag),
      'Expect a native root tag, instead got %s', tag
    );
  },

  reactTagIsNativeTopRootID: function(reactTag: number): boolean {
    // We reserve all tags that are 1 mod 10 for native root views
    return reactTag % 10 === 1;
  },
};

module.exports = ReactNativeTagHandles;