StreamProvider<QuerySnapshot>.value flutter 的初始数据

Question

StreamProvider.value 的初始数据应该是什么
我无法将其初始化为 null

 Widget build(BuildContext context) {
    return StreamProvider<QuerySnapshot>.value(
       value: DatabaseService.withoutUID().brews,
       initialData: null,
       ......

initialData:null 显示错误： The argument type 'Null' can't be assigned to the parameter type 'QuerySnapshot<Object?>'.

下面是 DatabaseService 辅助类

class DatabaseService{

  final String uid;

  DatabaseService(this.uid);
  DatabaseService.withoutUID():uid="" ;


  //collection reference
  final CollectionReference brewCollection = FirebaseFirestore.instance.collection('brews');

  Future updateUserData(String sugars, String name, int strength) async{
    return await brewCollection.doc(uid).set({
      "sugars": sugars,
      "name" : name,
      "strength" : strength,
    });
  }

  //get brews stream
  Stream<QuerySnapshot>? get brews{
    return brewCollection.snapshots();
  }

}

我在这里调用该流

class Home extends StatelessWidget {

final AuthService _auth = AuthService();

  @override
  Widget build(BuildContext context) {
    return StreamProvider<QuerySnapshot>.value(
      value: DatabaseService.withoutUID().brews,
      initialData: null,
      child: Scaffold(
        backgroundColor: Colors.brown[50],
        appBar: AppBar(
          backgroundColor: Colors.brown[400],
          title: Text("Brew Crew"),
          elevation: 0.0,
          actions: [
            ElevatedButton.icon(
              onPressed: () async {
                await _auth.signOut();
              }, .......

在本教程中，我关注他们正在使用 flutter 版本，initialData在我的情况下，这不是强制性的，但在我们使用时(flutter v 2.2.3)必须提供。所以我想知道我应该在那里提供什么价值。initialDataStreamProvider

顺便说一句，我正在关注yt 频道中的本教程The net ninja

Answer 1

我认为你应该更换QuerySnapshot with List<Brew>. ，你的initialData: [] 一切都应该工作正常。

  class DatabaseService {
  final String uid;

  DatabaseService(this.uid);

  DatabaseService.withoutUID() : uid = "";

  //collection reference
  final CollectionReference brewCollection =
      FirebaseFirestore.instance.collection('brews');

  Future updateUserData(String sugars, String name, int strength) async {
    return await brewCollection.doc(uid).set({
      "sugars": sugars,
      "name": name,
      "strength": strength,
    });
  }

  //get brews stream
  Stream<Brew>? get brews {
    return brewCollection.snapshots();
  }

  List<Brew> _brewListFromSnapshot(QuerySnapshot snapshot) {
    return snapshot.documents.map((doc) {
      //print(doc.data);
      return Brew(
          name: doc.data['name'] ?? '',
          strength: doc.data['strength'] ?? 0,
          sugars: doc.data['sugars'] ?? '0');
    }).toList();
  }
}

你的家.dart

class Home extends StatelessWidget {

final AuthService _auth = AuthService();

  @override
  Widget build(BuildContext context) {
    return StreamProvider<List<Brew>>.value(
      value: DatabaseService.withoutUID().brews,
      initialData: [],
      child: Scaffold(
        backgroundColor: Colors.brown[50],
        appBar: AppBar(
          backgroundColor: Colors.brown[400],
          title: Text("Brew Crew"),
          elevation: 0.0,
          actions: [
            ElevatedButton.icon(
              onPressed: () async {
                await _auth.signOut();
              }, .......

Answer 2

您可以简单地返回“StreamProvider<QuerySnapshot?>.value”，而不是返回“StreamProvider.value”。那么初始值将接受“null”值。