React-native this.props 在回调 function 中为空

Question

I am trying to implement Facebook login in my class. I created a button component, but when I call the Facebook api and I try to dispatch a register function I get un defined props. Here is my component:

import React, { Component } from 'react';
import { View, StyleSheet } from 'react-native';
import { LoginManager, AccessToken, GraphRequest, GraphRequestManager } from 'react-native-fbsdk';
import Icon from 'react-native-vector-icons/FontAwesome';
import { connect } from 'react-redux';
import AsyncStorage from '@react-native-async-storage/async-storage';
import {register} from '../Actions/authActions';

class Login extends Component {
    constructor(props) {
        super(props);
    }

    _fbAuth = () => {
        LoginManager.logInWithPermissions(['public_profile','email']).then(function(result){
            if(result.isCancelled){
                console.log('loging cancelled')
            }
            else {
                AccessToken.getCurrentAccessToken().then((data) => {
                    let accessToken = data.accessToken;
                    let facebookId = data.userID;
                    const responseInfoCallback = (error, result) => {
                        if (error) {
                            alert('Error logging in with Facebook');
                        }
                        else {
                            console.log('Props here are empty', this.props);
                            this.props.registerSubmit({
                                "customerName": result.name,
                                "customerTel": '000000000',
                                "customerEmail": result.email,
                                "customerPassword": facebookId
                            }).then(response => {
                                console.log('RESPONSE', response);
                                if (response && response.Success) {
                                    this.props.navigation.navigate('App');
                                    AsyncStorage.setItem('customerEmail', data.email);
                                    AsyncStorage.setItem('customerPassword', data.password);
                                } else {
                                    this.props.navigation.navigate('Auth');
                                }
                            });
                        }
                    }
                    const infoRequest = new GraphRequest('/me', {
                        accessToken: accessToken, 
                        parameters: {
                            fields: {
                                string: 'name,picture,email'
                            }}
                        }, responseInfoCallback);
                    new GraphRequestManager().addRequest(infoRequest).start();
                });
            }}, function (error) {
                console.log('Error logging with facebook');
            });
     }


    render() {
    return (
        <View style={styles.container}>
        <Icon.Button name="facebook" backgroundColor="#3b5998" onPress={this._fbAuth.bind(this)} style={styles.signInButton}>
          Facebook login
        </Icon.Button>
    </View>
    )
}
};

const mapDispatchToProps = (dispatch) => {
    // Action
    return {
        // Login
        registerSubmit: (data) => dispatch(register(data)),
    };
};

const styles = StyleSheet.create({
container: {
  flex: 1,
  justifyContent: 'center',
  alignItems: 'center',
},
signInButton: {
  width: 358,
  height: 48
}
});

export default connect(null, mapDispatchToProps)(Login);

When I get into the callback function this.props is empty and therefor the registerSubmit is undefined. This is my first project using class components I usually use hooks. What am I doing wrong?

Answer 1

When you run this line:

LoginManager.logInWithPermissions(['public_profile','email']).then(function(result){

The new function (result) { scope has its own this .

In order to access your component's this , you can either save a reference to it outside the callback, and then use that from inside the callback:

const componentProps = this.props
LoginManager.logInWithPermissions(['public_profile','email']).then(function(result){

Or, you can use an "arrow function" for your callback, which does not have its own this , like so:

LoginManager.logInWithPermissions(['public_profile','email']).then(result => {

(Notice how we aren't using the function keyword anymore)