diligent-react-native/styles/index.js

import React, { useState, useEffect, createContext, useContext } from "react";
import { useColorScheme } from "react-native";
import { THEME } from "@constants/localStorage";
import { getObjectData } from "@service/asyncStorage";
import { lightColors, darkColors } from "./colors";

export const ThemeContext = createContext({
  isDark: false,
  colors: lightColors,
  setScheme: () => {},
});

export const ThemeProvider = (props) => {
  // Getting the device color theme, this will also work with react-native-web
  const deviceColorScheme = useColorScheme(); // Can be dark | light | no-preference

  /*
   * To enable changing the app theme dynamically in the app (run-time)
   * we're gonna use useState so we can override the default device theme
   */
  const [isDark, setIsDark] = useState(null);

  const handleTheme = async () => {
    const theme = await getObjectData(THEME);
    if (theme !== null) {
      setIsDark(theme.type === "dark");
    } else {
      setIsDark(deviceColorScheme === "dark");
    }
  };

  // Get the theme from async storage on mount
  useEffect(() => {
    handleTheme();
  }, []);

  const defaultTheme = {
    isDark,
    // Changing color schemes according to theme
    colors: isDark ? darkColors : lightColors,
    // Overrides the isDark value will cause re-render inside the context.
    setScheme: async (scheme) => {
      setIsDark(scheme === "dark");
    },
  };

  return (
    <ThemeContext.Provider value={defaultTheme}>
      {props.children}
    </ThemeContext.Provider>
  );
};

// Custom hook to get the theme object returns {isDark, colors, setScheme}
export const useTheme = () => useContext(ThemeContext);