index.js

import React from 'react';
import { TextInput, Button } from 'react-native-paper';
import { Text, View } from 'react-native';

class LoginPage extends React.Component {
  state = {
    login: '',
    password: '',
  }

  updateCredentials = (newCredentials) => {
    const crededntialUpdated = {
      ...this.state.credentials,
      ...newCredentials,
    };

    this.setState(crededntialUpdated);
  }

  onSubmit = () => {
    login(this.state);
  }

  render() {
    return (
      <View>
        <Text>Login page</Text>
        <TextInput
          label='E-mail'
          value={this.state.login}
          onChangeText={login => this.updateCredentials({ login })}
        />
        <TextInput
          label='Senha'
          password={this.state.password}
          onChangeText={password => this.updateCredentials({ password })}
        />

      <Button onPress={this.onSubmit}>Logar</Button>
    </View>
    );
  }
}

export default LoginPage;