Convert Firestore DocumentSnapshot to Map in Flutter

As per our discussion snapshot is not a DocumentSnapshot it is AsyncSnapshot

to get the DocumentSnaphot use snapshot.data

to get the actual map you can use snapshot.data.data()

Which will return the Map<String, dynamic> you are looking for.

Needed to simplify for purpose of example

class ItemsList extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    // get the course document using a stream
    Stream<DocumentSnapshot> courseDocStream = Firestore.instance
        .collection('Test')
        .document('4b1Pzw9MEGVxtnAO8g4w')
        .snapshots();

    return StreamBuilder<DocumentSnapshot>(
        stream: courseDocStream,
        builder: (context, AsyncSnapshot<DocumentSnapshot> snapshot) {
          if (snapshot.connectionState == ConnectionState.active) {

            // get course document
            var courseDocument = snapshot.data.data;

            // get sections from the document
            var sections = courseDocument['sections'];

            // build list using names from sections
            return ListView.builder(
              itemCount: sections != null ? sections.length : 0,
              itemBuilder: (_, int index) {
                print(sections[index]['name']);
                return ListTile(title: Text(sections[index]['name']));
              },
            );
          } else {
            return Container();
          }
        });
  }
}

The Results

Looks like maybe because you got a stream builder, so the Snapshot is a AsyncSnapshot<dynamic>, when you grab its .data, you get a dynamic, which returns a DocumentSnapshot, which then you need to call .data on this object to get the proper Map<String, dynamic> data.

builder: (context, snapshot) {
final DocumentSnapshot  ds = snapshot.data;
final Map<String, dynamic> map = ds.data;
}

You can also append to arrays using in-built functions, but looks like you wanna do some crazy sorting so all good.

Update May 2021

See Migration to cloud_firestore 2.0.0 here.

//Replace this:
- StreamBuilder<DocumentSnapshot>(
//With this:
+ StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>(

The type has to be defined when creating variables:

Future<void> example(
    -  DocumentReference documentReference,
    +  DocumentReference<Map<String, dynamic>> documentReference,
    -  CollectionReference collectionReference,
    +  CollectionReference<Map<String, dynamic>> collectionReference,
    -  Query query,
    +  Query<Map<String, dynamic>> query,
) {