Wrap things in this. Get map dimension state as props on children. ⚠️Doesn't re-render anything because God is a lie.

dimensions.reducer.js

import React, { Fragment } from 'react'
import { Dimensions } from 'react-native'
import { connect } from 'react-redux'

class DimensionWatcher extends React.Component {
  handleDimensionsChange = dimensions => this.props.dispatch({
    type: `DIMENSIONS_CHANGED`,
    payload: dimensions,
  })

  componentWillMount () {
    alert(3)
    Dimensions.addEventListener(`change`, this.handleDimensionsChange)
  }

  componentWillUnmount () {
    alert(4)
    Dimensions.removeEventListener(`change`, this.handleDimensionsChange)
  }

  render () {
    return (
      <Fragment>
        {this.props.children}
      </Fragment>
    )
  }
}

const mapStateToProps = state => ({
  dimensions: state.dimensions,
})

export default connect(mapStateToProps)(DimensionWatcher)

DimensionWatcher.js

import React, { Fragment } from 'react'
import { Dimensions } from 'react-native'
import { connect } from 'react-redux'

class DimensionWatcher extends React.Component {
  handleDimensionsChange = dimensions => this.props.dispatch({
    type: `DIMENSIONS_CHANGED`,
    payload: dimensions,
  })

  componentWillMount () {
    Dimensions.addEventListener(`change`, this.handleDimensionsChange)
  }

  componentWillUnmount () {
    Dimensions.removeEventListener(`change`, this.handleDimensionsChange)
  }

  render () {
    return (
      <Fragment>
        {this.props.children}
      </Fragment>
    )
  }
}

const mapStateToProps = state => ({
  dimensions: state.dimensions,
})

export default connect(mapStateToProps)(DimensionWatcher)