App.js

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

const App = () => {
  const [email, setEmail] = useState('');
  const [password, setPassword] = useState('');
  const [isAuthenticated, setIsAuthenticated] = useState(false);

  const login = async () => {
    try {
      const user = await firebase
        .auth()
        .signInWithEmailAndPassword(email, password);

      setIsAuthenticated({isAuthenticated: true});
      console.log(user);
    } catch (e) {
      console.log(e);
    }
  };

  return (
    <View style={styles.container}>
      <TextInput
        style={styles.input}
        placeholder="Digite seu e-mail"
        value={email}
        onChangeText={email => setEmail(email)}
      />
      <TextInput
        style={styles.input}
        placeholder="Digite sua senha"
        value={password}
        onChangeText={password => setPassword(password)}
      />
      <TouchableOpacity style={styles.button} onPress={login}>
        <Text style={styles.buttonText}>Logar</Text>
      </TouchableOpacity>
      <Text> {`Status do Login: ${isAuthenticated}`}</Text>
    </View>
  );
};

const styles = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent: 'center',
    alignItems: 'center',
    backgroundColor: '#333',
    padding: 20,
  },
  input: {
    height: 45,
    backgroundColor: '#FFF',
    alignSelf: 'stretch',
    borderColor: '#DDD',
    borderWidth: 1,
    paddingHorizontal: 20,
    marginBottom: 10,
  },
  button: {
    height: 45,
    backgroundColor: '#069',
    alignSelf: 'stretch',
    borderColor: '#EEE',
    paddingHorizontal: 20,
    justifyContent: 'center',
    alignItems: 'center',
  },
  buttonText: {
    color: '#FFF',
    fontWeight: 'bold',
  },
});

export default App;