How to listen for document changes in Cloud Firestore using Flutter?

I would like to have a listener method that checks for changes to a collection of documents if changes occur.

Something like:

import 'package:cloud_firestore/cloud_firestore.dart';


Future<Null> checkFocChanges() async {
Firestore.instance.runTransaction((Transaction tx) async {
CollectionReference reference = Firestore.instance.collection('planets');
reference.onSnapshot.listen((querySnapshot) {
querySnapshot.docChanges.forEach((change) {
// Do something with change
});
});
});
}

The error here is that `onSnapshot` isn't defined on `CollectionReference`.

Any ideas?

Reading through [`cloud_firestore`'s documentation](

[To see links please register here]

) you can see that a `Stream` from a `Query` can be obtained via `snapshots()`.

For you to understand, I will transform your code just a tiny bit:

CollectionReference reference = Firestore.instance.collection('planets');
reference.snapshots().listen((querySnapshot) {
querySnapshot.documentChanges.forEach((change) {
// Do something with change
});
});

You should also not run this in a transaction. The *Flutter way* of doing this is using a `StreamBuilder`, straight from the [`cloud_firestore` *Dart* pub page](

[To see links please register here]

):

StreamBuilder<QuerySnapshot>(
stream: Firestore.instance.collection('books').snapshots(),
builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
if (!snapshot.hasData) return new Text('Loading...');
return new ListView(
children: snapshot.data.documents.map((DocumentSnapshot document) {
return new ListTile(
title: new Text(document['title']),
subtitle: new Text(document['author']),
);
}).toList(),
);
},
);

If you want to know any more, you can [take a look at the source](

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), it is well documented, where it is not self-explanatory.

Also take note that I changed `docChanges` to `documentChanges`. You can see that in the [`query_snapshot` file](

[To see links please register here]

). If you are using an IDE like IntelliJ or Android Studio, it is also pretty easy to click through the files in it.

Using this you can listen changes inside a single document.

DocumentReference reference = FirebaseFirestore.instance.collection('collection').doc("document");
reference.snapshots().listen((querySnapshot) {

setState(() {
field =querySnapshot.get("field");
});
});