Detect if the user is connected to the internet?

Try await NetInfo.isConnected.fetch()

ref : https://facebook.github.io/react-native/docs/netinfo.html#isconnected

You can check using NetInfo . for that you have to add connectionChange event listener like this

componentDidMount() {
        NetInfo.isConnected.addEventListener('connectionChange', this.handleConnectionChange.bind(this));
        NetInfo.isConnected.fetch().done(
            (isConnected) => { this.setState({ isConnected: isConnected }); }
        );

and then remove the event listener in componentWillUnmount

componentWillUnmount() {
        NetInfo.isConnected.removeEventListener('connectionChange', this.handleConnectionChange);
    }

And finally the handler method for connection change. I am storing the status in device local storage you can do whatever you want.

handleConnectionChange = (isConnected) => {
        if (isConnected) {
            //ToastAndroid.show('Data sync in process...', ToastAndroid.SHORT);
            AsyncStorage.getItem('offlineData')
                .then((json) => JSON.parse(json))
                .then((data) => {
                    console.log(JSON.stringify(data));
                });
        }
        else { ToastAndroid.show('You are offline.', ToastAndroid.SHORT); }

        this.setState({ isConnected: isConnected });
    }

Don't forget to add NetInfo from react-native :)

Another solution to your case (one without using isConnected property) is to use the object returned from the event handler directly like that:

componentDidMount() {
  NetInfo.addEventListener('connectionChange', this.handleNetworkChange);
}

componentWillUnmount() {
  NetInfo.removeEventListener('connectionChange', this.handleNetworkChange);
}

handleNetworkChange = (info) => {
    if (info.type === 'none') {
      this.props.navigation.navigate('Saved');
    }
};

According to NetInfo documentation:

connectionChange event fires when the network status changes. The argument to the event handler is an object with keys:

type: A ConnectionType (listed above)

effectiveType: An EffectiveConnectionType (listed above)

The connection type can be one of the following : none, wifi, cellular, unknown.

Ideally you can store this information to your redux store and the listener to a root component.

We had a weird bug when using isConnected similar to the one you mentioned @Gabriel Bleu but for us, the NetInfo.isConnected.fetch() returned false only when the Android device was awake after some period of inactivity.We used it to display offline warning for users, so the warning never left. I found this solution on a Spencer Carli's course and it seems to work better but depending on your needs, you might want to use isConnected combined with the above code.