react-native/packages/virtualized-lists/Lists/VirtualizedListContext.js

/**
 * Copyright (c) Meta Platforms, Inc. and affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 *
 * @flow strict-local
 * @format
 */

import type VirtualizedList from './VirtualizedList';

import * as React from 'react';
import {createContext, useContext, useMemo} from 'react';

type Context = $ReadOnly<{
  cellKey: ?string,
  getScrollMetrics: () => {
    contentLength: number,
    dOffset: number,
    dt: number,
    offset: number,
    timestamp: number,
    velocity: number,
    visibleLength: number,
    zoomScale: number,
  },
  horizontal: ?boolean,
  getOutermostParentListRef: () => VirtualizedList,
  registerAsNestedChild: ({cellKey: string, ref: VirtualizedList}) => void,
  unregisterAsNestedChild: ({ref: VirtualizedList}) => void,
}>;

export const VirtualizedListContext: React.Context<?Context> =
  createContext(null);
if (__DEV__) {
  VirtualizedListContext.displayName = 'VirtualizedListContext';
}

/**
 * Resets the context. Intended for use by portal-like components (e.g. Modal).
 */
export function VirtualizedListContextResetter({
  children,
}: {
  children: React.Node,
}): React.Node {
  return (
    <VirtualizedListContext.Provider value={null}>
      {children}
    </VirtualizedListContext.Provider>
  );
}

/**
 * Sets the context with memoization. Intended to be used by `VirtualizedList`.
 */
export function VirtualizedListContextProvider({
  children,
  value,
}: {
  children: React.Node,
  value: Context,
}): React.Node {
  // Avoid setting a newly created context object if the values are identical.
  const context = useMemo(
    () => ({
      cellKey: null,
      getScrollMetrics: value.getScrollMetrics,
      horizontal: value.horizontal,
      getOutermostParentListRef: value.getOutermostParentListRef,
      registerAsNestedChild: value.registerAsNestedChild,
      unregisterAsNestedChild: value.unregisterAsNestedChild,
    }),
    [
      value.getScrollMetrics,
      value.horizontal,
      value.getOutermostParentListRef,
      value.registerAsNestedChild,
      value.unregisterAsNestedChild,
    ],
  );
  return (
    <VirtualizedListContext.Provider value={context}>
      {children}
    </VirtualizedListContext.Provider>
  );
}

/**
 * Sets the `cellKey`. Intended to be used by `VirtualizedList` for each cell.
 */
export function VirtualizedListCellContextProvider({
  cellKey,
  children,
}: {
  cellKey: string,
  children: React.Node,
}): React.Node {
  // Avoid setting a newly created context object if the values are identical.
  const currContext = useContext(VirtualizedListContext);
  const context = useMemo(
    () => (currContext == null ? null : {...currContext, cellKey}),
    [currContext, cellKey],
  );
  return (
    <VirtualizedListContext.Provider value={context}>
      {children}
    </VirtualizedListContext.Provider>
  );
}