react native でログインフォームを作る

import React, { Component } from 'react';

import {
  AppRegistry,
  Text,
  Image,
  View,
  Button,
  StyleSheet,
  TextInput,
  Linking,
  Alert,
  Navigator
} from 'react-native';

import t from 'tcomb-form-native';

const Form = t.form.Form;

const Email = t.subtype(t.Str, (email) => {

  const reg = /^(([^<>()\[\]\\.,;:\s@"]+(\.[^<>()\[\]\\.,;:\s@"]+)*)|(".+"))@((\[[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}])|(([a-zA-Z\-0-9]+\.)+[a-zA-Z]{2,}))$/;

  return reg.test(email);
});

const LoginFields = t.struct({
  username: Email,
  password: t.String,
});

const options = {
  fields: {
    password: {
      type: 'password',
      placeholder: 'Password',

    },
    username: {
      placeholder: 'e.g: abc@gmail.com',
      error: 'Insert a valid email'
    }
  }
};

export default class Login extends Component {

  _onSubmit() {
     const value = this.refs.form.getValue();
     if (value) {
     console.log(value.password);
     console.log(value.username);
     }
  }

  render() {
    return (
      <View style={styles.containerView}>
      <Form
        ref="form"
        type={LoginFields}
        options={options}
      />
        <Text style={{color: 'blue', marginBottom: 10}}
          onPress={() => Linking.openURL('https://www.google.co.in')}>
          Forgot Password?
        </Text>
        <Button
            onPress={this._onSubmit.bind(this)}
            title="Login"
            style={styles.loginButton}
            accessibilityLabel="Ok, Great!"
          />
      </View>
    );
  }
};

const styles= StyleSheet.create({
  containerView: {
    flex: 1,
    justifyContent: 'center',
    backgroundColor: '#ffebcd',
    borderStyle: 'solid',
    borderColor: '#000000'
  },
  loginText: {
    fontSize: 20,
    marginBottom: 10
  },
  inputFields: {
    fontSize: 20,
    borderStyle: 'solid',
    borderColor: '#000000',
    borderRadius: 30,
    marginBottom: 10
  },
  loginButton: {
    backgroundColor: '#34A853'
  }
});