class BackController extends Component {
  static propTypes = {
    onBack: PropTypes.func
  }
  constructor (props) {
    super(props)
    this.handleBack = this.handleBack.bind(this)
  }
  componentDidMount () {
    BackHandler.addEventListener('hardwareBackPress', this.handleBack)
  }
  componentWillUnmount () {
    BackHandler.removeEventListener('hardwareBackPress', this.handleBack)
  }
  handleBack () {
    if (typeof this.props.onBack === 'function') {
      this.props.onBack()
    }
  }
  render () {
    return null
  }
}