BackButton.js

import React from "react";
import PropTypes from "prop-types";
import { BackHandler } from "react-native";

class BackButton extends React.Component {
  static contextTypes = {
    router: PropTypes.shape({
      history: PropTypes.shape({
        goBack: PropTypes.func.isRequired,
        index: PropTypes.number.isRequired
      }).isRequired
    }).isRequired
  };

  componentDidMount() {
    BackHandler.addEventListener("hardwareBackPress", this.handleBack);
  }

  componentWillUnmount() {
    BackHandler.removeEventListener("hardwareBackPress", this.handleBack);
  }

  handleBack = () => {
    const { history } = this.context.router;

    if (history.index === 0) {
      return false; // home screen
    } else {
      history.goBack();
      return true;
    }
  };

  render() {
    return this.props.children || null;
  }
}

export default BackButton;