Flutter 从 QuerySnapshot 转换为 Future <list<map<dynamic, dynamic> >> </list<map<dynamic,>

Question

How do I return a QuerySnapshot as a Future >>?

Code snippet:

Future <List<Map<dynamic, dynamic>>>() {
List<Map<dynamic,dynamic>> list;
.....

.....
QuerySnapshot collectionSnapshot = await collectionRef.getDocuments();

list = collectionSnapshot.documents;  <--- ERROR
return list;

}

I think I need to use a Map of but couldn't get around it to work.

Answer 1

collectionSnapshot.documents return List and not List types, you will need to convert List of documentsnapshots to List<Map<dynamic, dynamic>> . My be something like this:

Future <List<Map<dynamic, dynamic>>> getCollection() async{
List<DocumentSnapshot> templist;
List<Map<dynamic, dynamic>> list = new List();
CollectionReference collectionRef = Firestore.instance.collection("path");
QuerySnapshot collectionSnapshot = await collectionRef.getDocuments();

templist = collectionSnapshot.documents; // <--- ERROR

list = templist.map((DocumentSnapshot docSnapshot){
  return docSnapshot.data;
}).toList();

return list;
}  

Answer 2

@Ganapat, your answer solved my problem. Thank you

Answer 3

Ganapat's answer worked out for me with a few minor changes.

Future <List<Map<dynamic, dynamic>>> getCollection() async{
List<DocumentSnapshot> templist;
List<Map<dynamic, dynamic>> list = new List();
CollectionReference collectionRef = Firestore.instance.collection("path");
QuerySnapshot collectionSnapshot = await collectionRef.get(); // <--- This method is now get().

templist = collectionSnapshot.documents; // <--- ERROR

list = templist.map((DocumentSnapshot docSnapshot){
  return docSnapshot.data() as Map<Dynamic,Dynamic>; // <--- Typecast this.
}).toList();

 

return list;
}  

Answer 4

Proper way of using QuerySnapshot in the FutureBuilder is as follows:

@override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
          child: FutureBuilder<QuerySnapshot>(
        future: FirebaseFirestore
                .instance
                .collection('users') // 👈 Your collection name here
                .get(), 
        builder: (_, snapshot) {
          if (snapshot.hasError) return Text('Error = ${snapshot.error}');
          if (snapshot.connectionState == ConnectionState.waiting) {
            return const Text("Loading");
          }
          return ListView(
              children: snapshot.data!.docs.map((DocumentSnapshot document) {
            Map<String, dynamic> data = document.data()! as Map<String, dynamic>;
            return ListTile(
              title: Text(data['avatar']), // 👈 Your valid data here
            );
          }).toList());
        },
      )),
    );
  }

Also refer: How to use StreamBuilder and FutureBuilder for single and multiple documents