Flutter Firebase 登录 function

Question

How to access if users exist on users/$usersUids[index]

_db.collection('users').doc(user1.uid).set({
    "displayName": user1.displayName,
    "email": user1.email,
    "uid": user1.uid,
    'date': date,
    "photoUrl": user1.photoURL,
    "lastSignIn": DateTime.now(), 
  });

or if the user has already login/signup then I want to run

_db.collection('users').doc(user1.uid).set({
    "displayName": user1.displayName,
    "email": user1.email,
    "uid": user1.uid,
    'date': date,
    "photoUrl": user1.photoURL,
    "lastSignIn": DateTime.now(),
    'favItems': []
  });

If the question is wrong then please fix this Thank you

Answer 1

You can use firebase authentication to see if the user is logged in, you will need to set that up in your Firebase Console . Here's a video I used to help me set it up: Flutter Authentication with Email and Password Tutorial Below is an example of what your code may look like once you have the authentication set up.

import 'package:firebase_auth/firebase_auth.dart';

FirebaseAuth auth = FirebaseAuth.instance;
    User? user = auth.currentUser;

    // CHECK LOGIN STATUS OF USER AND DECIDE WHICH SCREEN TO SHOW USER
    // ignore: unnecessary_null_comparison
    if (user != null) {
      // SHOW THE USERS PERSONAL HOME PAGE
      currentScreen = 1;
    } else {
      // USER IS NOT LOGGED IN, SHOW THE SIGN IN SCREEN
      currentScreen = 2;
    }

Let me know if I need to clarify anything else for you.