react-native example formik and yup

formik_yup_example.js

import { Formik } from 'formik';
import * as Yup from 'yup';

class SignInScreen extends React.Component {
    constructor(props) {
        super(props);
        this.state = {
            username: null,
            password: null,
            rememberMe: false,
            statusMessage: null,
            loading: false
        };
    }

    static navigationOptions = {
        title: 'Please sign in',
    };

    render() {
        return (
            <View style={styles.container}>
                <Formik enableReinitialize 
                    initialValues={{username:this.state.username,email:''}} 
                    validationSchema={SignupSchema} 
                    onSubmit={values=>console.log(values)}>
                {({handleChange, handleBlur, handleSubmit, values, errors, touched})=>(
                    <Card>
                        <Input
                            label="Username"
                            onChangeText={handleChange('username')}
                            onBlur={handleBlur('username')}
                            value={values.username}
                        />
                        {errors.username && touched.username ? (<Text>{errors.username}</Text>): null}
                        <Input
                            label="Email"
                            onChangeText={handleChange('email')}
                            onBlur={handleBlur('email')}
                            value={values.email}
                        />
                        {errors.email && touched.email ? (<Text>{errors.email}</Text>): null}
                        <Button onPress={handleSubmit} style={{margin:10}} title="Submit"/>
                    </Card>
                )}
                </Formik>
            </View>
        );
    }
}

const SignupSchema = Yup.object().shape({
    username: Yup.string()
        .min(2,'Too Short!')
        .max(50, 'Too Long!')
        .required('Required'),
    email: Yup.string()
        .email('Invalid email')
        .required('Required')
})


export default SignInScreen;