How to use Redux in react-native to dispatch NetInfo connectivy change action?

Question

I'd like to be able to 'continuosly' monitor device connection in my react-native app.

I'm already using redux-thunk and redux with success.

Actually I'me able to do this

import { NetInfo } from 'react-native';

import {
    CONNECTION_CHECKING,
    CONNECTION_AVAILABLE,
    CONNECTION_UNAVAILABLE, 
} from './types';


export const connectionChecking = () => {
    return (dispatch) => {

        dispatch ({
            type: CONNECTION_CHECKING
        });

        NetInfo.getConnectionInfo()
            .then((connectionInfo) => {

                console.log('Connection info: ', connectionInfo);
                switch (connectionInfo.type) {
                    case 'cellular':
                        dispatch ({
                            type: CONNECTION_AVAILABLE,
                            payload: connectionInfo.type
                        });
                        break;
                    case 'wifi':
                        dispatch ({
                            type: CONNECTION_AVAILABLE,
                            payload: connectionInfo.type
                        });
                        break;
                    default:
                        dispatch ({
                            type: CONNECTION_UNAVAILABLE,
                        });
                }
            })
            .catch((error) => console.warn(error));

    };
};

But, I don't know how to dispatch new action when connection changes..

From the react-native doc i see this:

NetInfo.addEventListener(
  'connectionChange',
  handleConnectivityChange
);

But ... how to dispatch an action inside an event listener?

I tried to add this into the same action file

NetInfo.addEventListener(
    'connectionChange', (connectionInfo)  => {
        return (dispatch) => {

            console.log('Connection info changed ', connectionInfo);
            switch (connectionInfo.type) {
                case 'cellular':
                case 'wifi':
                    dispatch ({
                        type: CONNECTION_AVAILABLE,
                        payload: connectionInfo.type
                    });
                    break;
                default:
                    dispatch ({
                        type: CONNECTION_UNAVAILABLE,
                    });
            }

        };
    }
);

I got no results, no console.log, and so I think it's the wrong way

Answer 1

You just need to set up your event listener somewhere with access to the dispatch function.

Directly from a component

The easiest thing to do (allowing for clean unsubscribing) is to set them up in your topmost connected component:

class MyApp extends Component {
  constructor(props) {
    super(props);

    // Dispatch an action from your event handler (and do whatever else)
    this._handleConnectionChange = (connectionInfo) => props.dispatch({ 
      type: 'CONNECTION_CHANGE', 
      connectionInfo
    });

    NetInfo.addEventListener('connectionChange', this._handleConnectionChange);
  }

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

export default connect()(MyApp); // MyApp must be connected

A little abstraction - adding the listener within a Thunk

Personally I like to wrap this kind of thing in a thunk to avoid listener handling cluttering my components. The important point here is that thunks, like connected components, have access to dispatch , so by defining the listener within the inner part of a thunk we can dispatch actions (or more thunks) in response to changes.

// connectionActions.js

let handleConnectionChange;

export function registerListeners() {
  return (dispatch) => {
    handleConnectionChange = (connectionInfo) => {
      dispatch(connectionChanged(connectionInfo));
    }
    NetInfo.addEventListener('connectionChange', handleConnectionChange);
  }
}

export function unregisterListeners() {
  return (dispatch) => {
    handleConnectionChange && NetInfo.removeEventListener('connectionChange', handleConnectionChange);
  }
}

function connectionChanged(connectionInfo) {
  return (dispatch) => {
    switch (connectionInfo.type) {
      case 'cellular':
        dispatch({
          type: CONNECTION_AVAILABLE,
          payload: connectionInfo.type
        });
        break;
      // ...Other cases
    }
  }
}

And then you can dispatch registerListeners() and unregisterListeners() from MyApp rather than defining the details of the listeners there:

// app.js
// ...other imports
import * as connectionActions from './connectionActions'

class MyApp extends Component {
  constructor(props) {
    super(props);
    // Dispatch your thunk to take care of the registration
    props.dispatch(connectionActions.registerListeners());
  }

  componentWillUnmount() {
    this.props.dispatch(connectionActions.unregisterListeners());
  }
}

export default connect()(MyApp)

A bit more abstraction - a higher-order component for listening

In apps where I have multiple possible top level components (eg different build variants with different homepages, or a Login screen that's not part of the main navigator), I like to take this kind of boilerplate and wrap it in a higher order component:

// hoc/withNetListeners.js

export default function withNetListeners(SourceComponent): {
  class HOC extends React.Component {
    constructor(props) {
      super(props);
      props.dispatch(connectionActions.registerListeners());
    }

    componentWillUnmount() {
      this.props.dispatch(connectionActions.unregisterListeners());
    }

    render() {
      return <SourceComponent {...this.props} />;
    }
  }
  return hoistStatics(HOC, SourceComponent); // Package hoist-non-react-statics
}

And then in whichever component(s) act as your root(s):

// app.js
class MyApp extends Component {
  // ... Just your UI, no listeners ...
}

// Inject the listeners with a HOC. Make you `connect` last, because 
// `withNetListeners` needs to be given access to `dispatch`.
export default connect()(withNetListeners(MyApp))