firebase auth return null on signInWithPhoneNumber - firebase

Question

I am trying to login with phone number with firebase signInWithPhoneNumber() method for login. In which i have checked whether user auth state has been change or not. If user auth is change then login and redirect to home page. but i m getting auth null
onLoginBtnClicked() {
const { contact, password } = this.props;
const error = Validator('password', password) || Validator('contact', contact);
if (error !== null) {
Alert.alert(error);
} else {
console.log('else');
// this.props.loginUser({ contact, password});
const mobileNo = '+91'+contact;
firebase.auth().signInWithPhoneNumber(mobileNo)
.then(data => console.log(data),
firebase.auth().onAuthStateChanged((user) => {
console.log('user'+user);
if (user && !CurrentUser.isFirstTimeUser) {
const userRef = firebase.database().ref(`/users/`);
userRef.on("value", (snapshot) => {
console.log(snapshot.val());
snapshot.forEach(function(item) {
var itemVal = item.val();
if(itemVal.mobile == contact){
NavigationService.navigate('Home');
}
});
}, (errorObject) => {
console.log("The read failed: " + errorObject.code);
});
//NavigationService.navigate('Home');
}
})
)
.catch(error => console(error.message) );
}
}

Answer 1

There are two things to note here
onAuthStateChanged is a listener which listen for the user auth changes.
signInWithPhoneNumber sends the code to the user's phone, you have to confirm it to authenticate the user.
You need to add the listener in the react lifecycle for the component once it is mounted and remove it when it is unmounted
componentDidMount() {
this.unsubscribe = firebase.auth().onAuthStateChanged((user) => {
if (user) {
this.setState({ user: user.toJSON() });
} else {
// Reset the state since the user has been logged out
}
});
}
componentWillUnmount() {
if (this.unsubscribe) this.unsubscribe();
}
// Send Message here
firebase.auth().signInWithPhoneNumber(mobileNo)
.then(confirmResult => this.setState({ confirmResult })
.catch(error => // handle the error here)
// Authenticate User typed Code here
const { userCode, confirmResult } = this.state;
if (confirmResult && userCode.length > 0) {
confirmResult.confirm(codeInput)
.then((user) => {
// handle user confirmation here or in the listener
})
.catch(error => // handle the error here)
}