react-native open modal automatically when state is changed

I am using react-native-modalbox. What I want to do is open modal automatically when state is changed rather than using a button.

Below is my code it works fine with the button. But I want the modal to open when stateChange state is changed.

import React from 'react';
import Button from 'react-native-button';
import Modal from 'react-native-modalbox';
import {Text, StyleSheet, ScrollView, View, Dimensions, TextInput} from 'react-native';
var screen = Dimensions.get('window');

export default class TestScreen extends React.Component {

  constructor() {
    super();
    this.state = {
      isDisabled: false,
      number:''

//I want to open modal when this state is changed

      stateChange:''
    };
  }

  render() {

    return (
      <View style={styles.wrapper}>

// When I press this button it opens a modal  

        <Button onPress={() => this.refs.modal3.open()} style={styles.btn}>Position centered + backdrop + disable</Button>

        <Modal style={[styles.modal, styles.modal3]} position={"center"} ref={"modal3"} isDisabled={this.state.isDisabled}>
          <Text style={styles.text}>Modal centered</Text>
          <Button onPress={() => this.setState({isDisabled: !this.state.isDisabled})} style={styles.btn}>Disable ({this.state.isDisabled ? "true" : "false"})</Button>
        </Modal>

      </View>
    );
  }
}

Edited

I want to use react lifecycle method to listen to this update and automatically update it. So I am using componentDidUpdate. I want to update this.state.number when ever mobx store is updated. However, the code below wouldn't work.

componentDidUpdate(nextProps, nextState) {
    this.setState({number:store.requestObject.number},
    console.log(this.state.number), 'state changed')
  }