我无法在 React Native 中设置状态

Question

在这个项目中，我想使用从firebase 数据库中检索到的数据来设置userType 的状态。从firebase 获取工作正常，但我无法从那里设置userType 的状态

我已经尝试过了
this.setState=({userType:snapshot.val()})
this.state=({userType:snapshot.val()})

    import React from 'react';
    import { StyleSheet, Text, View, TouchableOpacity, TextInput, Image } from 'react-native';
    import * as firebase from 'firebase';


    export default class Home extends React.Component {
      constructor(props){
        super(props)
        this.state=({
          userId:firebase.auth().currentUser.uid,
          userType:'f'
        })
      }
      componentDidMount() {
        this.readUserData();
      };
      readUserData=()=> {
        userstype= 'users/'+ this.state.userId + '/userType'

        firebase.database().ref(userstype).on('value', function (snapshot) {
          this.setState=({userType:snapshot.val()})
        });

          alert(this.state.userType)
        }


      render() {
        return (

          <View style={styles.container}>
            <Text style={styles.titleText}>Taams</Text>
            <Text style={styles.edition}>Developer's Edition</Text>
            <Text style={styles.titleText}>Home</Text>
            <Text>Alpha 0.0.0.1</Text>
          </View>
          )}}

Answer 1

我已经更新了你的 setState 方法

试试下面的代码

 import React from 'react';
 import { StyleSheet, Text, View, TouchableOpacity, TextInput, Image } from 'react-native';
 import * as firebase from 'firebase';


    export default class Home extends React.Component {
      constructor(props){
        super(props)
        this.state=({
          userId:firebase.auth().currentUser.uid,
          userType:'f'
        })
      }
      componentDidMount() {
        this.readUserData();
      };
      readUserData=()=> {
        userstype= 'users/'+ this.state.userId + '/userType'

        firebase.database().ref(userstype).on('value', function (snapshot) {
          this.setState({userType:snapshot.val}, () => {
            alert(this.state.userType)
          })
        });


        }


      render() {
        return (

          <View style={styles.container}>
            <Text style={styles.titleText}>Taams</Text>
            <Text style={styles.edition}>Developer's Edition</Text>
            <Text style={styles.titleText}>Home</Text>
            <Text>Alpha 0.0.0.1</Text>
          </View>
          )}}

希望这对你有用！ 谢谢