React Native TypeScript TextInput not working

Question

I am trying to learn react native by doing a basic application. I followed many tutorials available online and made the following class for a login screen:

import React, { Component } from "react";
import { View, StyleSheet, TextInput, Button, Alert, TouchableHighlight, Text } from "react-native";
import { styles } from "../styles/CommonStyles";

class LoginScreen extends Component {
    constructor(props: Readonly<{}>) {
        super(props)
    }
    state = {
        email: ''
    }
    static navigationOptions = {
        title: 'Login',
        header: null
    }
    render() {
        const { navigate } = this.props.navigation
        return (
            <View style={styles.container}>

                <TextInput
                style={loginStyles.emailInput}
                multiline={false}
                autoCorrect={false}
                autoCapitalize='none'
                keyboardType='email-address'
                value={this.state.email}
                onChangeText={(text) => this.handleEmail(text)}
                placeholder='Enter Email'/>

                <TouchableHighlight
                style={loginStyles.buttonGenerateOTP}
                onPress={this.onGenerateOTP}>
                    <Text
                    style={loginStyles.textGenerateOTP}>GENERATE OTP</Text>
                </TouchableHighlight>
            </View>
        )
    }

    handleEmail(text: string) {
        console.log('Email: ' + text)
        this.setState({ email: text })
        console.log('State Email: ' + this.state.email)
    }

    onGenerateOTP() {
        Alert.alert(
            'Email Entered',
            this.state.email,
            [
                { text: 'OK', style: 'cancel' }
            ],
            { cancelable: false }
        )
    }
}

export default LoginScreen

const loginStyles = StyleSheet.create({
    emailInput: {
        fontSize: 15,
        backgroundColor: '#ECECEC',
        borderColor: '#999999',
        borderRadius: 4,
        borderWidth: 0.5,
        alignSelf: 'stretch',
        textAlign: 'center',
        margin: 10,
      },
      buttonGenerateOTP: {
          backgroundColor: '#008CBA',
          borderRadius: 4,
          alignSelf: 'stretch',
          justifyContent: 'center',
          alignItems: 'center',
          margin: 10,
          padding: 10,
    },
    textGenerateOTP: {
        fontSize: 20,
        color: '#FFFFFF',
    },
})

It only contains an input and a button, on which an alert should be shown with the entered email. But when I click the button, I am getting the following error:

undefined is not an object (evaluating 'this.state.email')
onGenerateOTP
LoginScreen.tsx:43:8
...

I am pretty new to react native and typescript, but looking at the code, I couldn't figure out any issues. What is it that I am doing wrong here?

EDIT The log in handleEmail(text) function is actually printing the state, although with the previous value of text(ie, when I enter QWERT, it will print QWER, and when I enter QWERTY, it will print QWERT), but the text param is logging correctly

Harikrishnan · Accepted Answer · 2020-11-18 13:23:33Z

1

I solved the issue. The issue was that I had to bind the functions. Changing the constructor as per below fixed the issue.

constructor(props: Readonly<{}>) {
    super(props)
    this.handleEmail = this.handleEmail.bind(this)
    this.onGenerateOTP = this.onGenerateOTP.bind(this)
}

edited Nov 18, 2020 at 13:23

answered Jun 22, 2019 at 8:12

Harikrishnan

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Comments

Martin Nowosad · Accepted Answer · 2019-06-22 08:07:18Z

0

you have to call in your constructor or componentWillMount life-cycle method

this.setState{{'email': 'your_value}}

Only change the state through the setState method

answered Jun 22, 2019 at 8:07

Martin Nowosad

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