App.js

import React, {Component} from 'react';
import { StyleSheet } from 'react-native';
import AppNavigator from './src/components/RootStack';
import { isSignedIn } from "./src/services/AuthService";
import NavigationService from './src/services/NavigationService';


type Props = {};
export default class App extends Component<Props> {

  constructor(props) {
    super(props);

    this.state = {
      signedIn: false,
      checkedSignIn: false
    };
  }

  componentDidMount() {
    isSignedIn()
      .then(res => this.setState({ signedIn: res, checkedSignIn: true }))
      .catch(err => alert("An error occurred"));

  }

  render() {

    return (
      <AppNavigator
        ref={navigatorRef => {
          NavigationService.setTopLevelNavigator(navigatorRef);
        }}
      />
    );
  }
}

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#F5FCFF',
  },
  welcome: {
    fontSize: 20,
    textAlign: 'center',
    margin: 10,
  },
});