How to implement onAuthStateChanged() in flutter?

Question

<https://stackoverflow.com/a/32254702/10026969>  I am not getting this.

@override
void initState()  async{
// TODO: implement initState
super.initState();

FirebaseUser user = await _auth.currentUser();
if(user!=null){
  print('Already logged in with email  '+ user.email);
  // go to welcome screen
 }
}

I am unable to keep use onAuthStateChange,How to keep the user logged in until he log out, if anyone has any idea how to implement this , please help.

If the answer helped you, please upvote it and mark it as correct thank you! — Peter Haddad, Apr 08 '20 at 05:45

score 1 · Answer 1 · answered Apr 07 '20 at 07:12

If you want to use onAuthStateChange in flutter, then try the following:

var auth = FirebaseAuth.instance;
auth.onAuthStateChanged.listen((user) {
if (user != null) {
  print("user is logged in");
} else {
  print("user is not logged in");
   }
});

onAuthStateChanged returns a Stream therefore you can use listen() to keep listening for any changes.

https://github.com/FirebaseExtended/flutterfire/blob/master/packages/firebase_auth/firebase_auth/lib/src/firebase_auth.dart#L23

score 0 · Answer 2 · answered Apr 07 '20 at 07:24

So onAuthStateChanged() returns a Stream. https://pub.dev/documentation/firebase_auth/latest/firebase_auth/FirebaseAuth/onAuthStateChanged.html

You can listen in to this stream for all of the events using a StreamBuilder. Based off the AsyncSnapshot returned from the builder function you can check if it hasData.

Create your FirebaseAuth object. This object has the property of onAuthStateChanged().
Pass the property _auth.onAuthStateChanged() to your StreamBuilder.

Pseudo Example Code:

final FirebaseAuth _auth = FirebaseAuth.instance;

Center(
  child: StreamBuilder(
    stream: _auth.onAuthStateChange(),
    builder: (context, asyncSnap) {
      //no available data yet
      if(!asyncSnap.hasData) {
        return Text("No data available yet.");
      } else if(asyncSnap.hasError) {
        return Text("Error");
      } else {
        //Use a switch here over all of the types of state coming back.
        return Text("Data from Snapshot: ${asyncSnap.data}");
      }
    }
  )
)

How to implement onAuthStateChanged() in flutter?

2 Answers2