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Redux and local storage

In this section, we will see how to use Redux to query and mutate the data and local storage to store the keys of our patients.

One of the key features of iCure is that it allows you to store data in a secure way. This means that one can store data in a way that only the user that has created it or users with whom data has been explicitly shared can access it. This is done by ultimately encrypting the collected data with the users' public keys. This way, only users with access to corresponding private keys can decrypt the data.

And to keep this key private, we will store it in the local storage of the device.


iCure MedTech SDK allows you to redefine how the keys will be stored, by default the implementation of the SDK uses the local storage of the browser. Since we are using React Native, there's no implementation of local storage, so we will need to implement it ourselves using MMKV and provide this custom implementation to the SDK.

Custom implementation of the key storage

As we said, we will use MMKV to store the keys. We will create a class that will implement the StorageFacade interface from the SDK.

import {StorageFacade} from '@icure/medical-device-sdk';
import {MMKV} from 'react-native-mmkv';

export class AsyncStorageImpl implements StorageFacade<string> {
storage = new MMKV();
setItem = (key: string, value: string) => {
return new Promise(resolve => resolve(, value))) as Promise<void>;
getItem = (key: string) => {
return new Promise(resolve => resolve( as Promise<string | undefined>;
removeItem = (key: string) => {
return new Promise(resolve => resolve( as Promise<void>;

export default new AsyncStorageImpl();

Keep this class warm, we will need it for the persistor of Redux and the instantiation of the MedTechApi.

Redux initialization

State of the application

We will start by creating a "root" level state that will keep the user credentials to make it possible to query data on our API.

import {createSlice, PayloadAction} from '@reduxjs/toolkit';
import storage from '../utils/storage';

// Configuration object for data persistence with Redux Persist
export const persistConfig = {
key: 'petra',
storage: storage,
whitelist: ['petra'],

export interface PetraState {
cache: string;
savedCredentials?: {
tokenTimestamp: number;
login: string;
token: string;

const initialState = {} as PetraState;

export const petra = createSlice({
name: 'app',
reducers: {
setSavedCredentials(state, {payload: savedCredentials}: PayloadAction<{login: string; token: string; tokenTimestamp: number} | undefined>) {
state.savedCredentials = savedCredentials;
revertAll() {
return initialState;

export const {setSavedCredentials, revertAll} = petra.actions;


One of the first principle of Redux is to have a single source of truth. This means that the state of the application should be stored in a single place. This is done by using a reducer. A reducer is a function that takes the current state and an action as parameters and returns the new state of the application.

So let's create a reducer that will combine all the reducers of the application.

import {combineReducers} from '@reduxjs/toolkit';
import {persistConfig, petra} from '../config/PetraState';
import {persistReducer} from 'redux-persist';

export const appReducer = combineReducers({
petra: petra.reducer,

export const persistedReducer = persistReducer(persistConfig, appReducer);

export type AppState = ReturnType<typeof appReducer>;


The store is the object that will hold the state of the application. It will be used by the components of the application to access the state and dispatch actions.

import {configureStore} from '@reduxjs/toolkit';
import {persistedReducer} from './reducer';
import {persistStore} from 'redux-persist';
import thunk from 'redux-thunk';

export const store = configureStore({
reducer: persistedReducer,
middleware: getDefaultMiddleware =>
getDefaultMiddleware({serializableCheck: false, immutableCheck: false}).concat(
export const persistor = persistStore(store);

export type AppDispatch = typeof store.dispatch;


To make it easier to access the state of the application, we will create some hooks that will return the state and the dispatch function.

import {AppDispatch} from './store';
import {TypedUseSelectorHook, useDispatch, useSelector} from 'react-redux';
import {AppState} from './reducer';

export const useAppDispatch = () => useDispatch<AppDispatch>();
export const useAppSelector: TypedUseSelectorHook<AppState> = useSelector;


Now that we have our store, we need to provide it to the components of the application. This is done by using a provider.

// ...
import { Provider } from 'react-redux';
import { PersistGate } from 'redux-persist/integration/react';
import { store, persistor } from './redux/store';
import { Text } from 'react-native';

// ...

const App = () => {
const isDarkMode = useColorScheme() === 'dark';

const backgroundStyle = {
backgroundColor: '#FFFDFE',
flex: 1,

return (
<Provider store={store}>
<PersistGate persistor={persistor} loading={<Text>Loading...</Text>}>
<StatusBar barStyle={isDarkMode ? 'light-content' : 'dark-content'} backgroundColor={backgroundStyle.backgroundColor} />
<ScrollView contentInsetAdjustmentBehavior="automatic" style={backgroundStyle}>
<Router />

export default App;