带有TypeScript的React Native this.setState不是一个函数

Question

I'm currently using React Native 0.39.2 w/ newest TypeScript and when I run my componentDidMount() method and setState I get an error around this.setState is not a function.

I tried binding with this.setState({isLoggedIn: true}).bind(this)

though since I'm using a boolean as the type it won't let me without giving a type error and even setting to any type still gets same error.

here's my code

First with my interface for State

import React, {
 Component
} from 'react';
import { AppRegistry, View, StyleSheet, Text } from 'react-native';
import { Actions } from 'react-native-router-flux';

import Firestack from 'react-native-firestack';

const firestack = new Firestack();

interface Props {

}

interface State {
  isLoggedIn?: boolean;
}


export default class MainList extends Component<Props, State> {

   state = {
     isLoggedIn: false,
   };

   constructor(props: any) {

      super(props);
      console.log("Is anyone logged in?: " + this.isLoggedIn);

   }

   isLoggedIn = this.state.isLoggedIn;

   componentDidMount() {

      if (!this.isLoggedIn) {

          Actions.welcome();

      }

      firestack.auth.listenForAuth(function(evt: any) {
      // evt is the authentication event
      // it contains an `error` key for carrying the
      // error message in case of an error
      // and a `user` key upon successful authentication

        if (!evt.authenticated) {
        // There was an error or there is no user
        //console.error(evt.error);

        this.setState({isLoggedIn: false});
        console.log("The state of isLoggedIn is: " +       this.isLoggedIn);

        } else {
        // evt.user contains the user details
        console.log('User details', evt.user);

        this.setState({isLoggedIn: true});
        console.log("The state of isLoggedIn is: " + this.isLoggedIn);

        }


    }); 

}

render() {

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

            <Text style={styles.textLabel}>The main view</Text>

        </View>
     )

   }

 }

 const styles = StyleSheet.create({

 View: {
    padding: 20
 },
 textLabel: {
    fontSize: 20,
    marginBottom: 10,
    height: 20
 },
 textInput: {
    height: 20,
    fontSize: 15,
    marginBottom: 20
  }

});

AppRegistry.registerComponent('MainList', ()=> MainList);

Is there anything I'm missing here?

Answer 1

The issue is because in the callback function for listenForAuth , this is no longer referring to the MainList object.

Try switching to arrow function expression which solve the this binding issue:

firestack.auth.listenForAuth((evt: any) => {
  ...
});

Here is a good read if you want to know more about arrow function.