问如何在react native中按下tab栏添加事件？

EN

import {NavigationEvents} from "react-navigation";


<NavigationEvents
      onWillFocus={payload => console.log('will focus',payload)}
      onDidFocus={payload => console.log('did focus',payload)}
      onWillBlur={payload => console.log('will blur',payload)}
      onDidBlur={payload => console.log('did blur',payload)}
    />

import React, {Component} from 'react';
import { View, StyleSheet, Text } from 'react-native';

export default class Screen2 extends React.Component {

  // willFocus - the screen will focus
  // didFocus - the screen focused (if there was a transition, the transition completed)
  // willBlur - the screen will be unfocused
  // didBlur - the screen unfocused (if there was a transition, the transition completed)
  componentDidMount () {
    // add listener 
    this.willFocusSubscription = this.props.navigation.addListener('willFocus', this.willFocusAction);
    this.didFocusSubscription = this.props.navigation.addListener('didFocus', this.didFocusAction);
    this.willBlurSubscription = this.props.navigation.addListener('willBlur', this.willBlurAction);
    this.didBlurSubscription = this.props.navigation.addListener('didBlur', this.didBlurAction);
  }

  componentWillUmount () {
    // remove listener
    this.willFocusSubscription.remove()
    this.didFocusSubscription.remove();
    this.willBlurSubscription.remove();
    this.didBlurSubscription.remove();
  }

  willBlurAction = () => {
    console.log('willBlur Screen', new Date().getTime())
  }

  didBlurAction = () => {
    console.log('didBlur Screen', new Date().getTime());
  }

  didFocusAction = () => {
    console.log('didFocus Screen', new Date().getTime());
  }

  willFocusAction = () => {
    console.log('willFocus Screen', new Date().getTime());
  }


  render() {
    return (
      <View style={styles.container}>
      <Text>Screen</Text>
      </View>
    )
  }
}