Question

我正在尝试从用户所属的组中获取来自 firebase 的所有帖子。我现在的问题是程序不会等到列表 groupsPosts 有数据并继续执行代码。

getTimelineWithGroupPosts() async {
   List groupIDs = [];
   List<QuerySnapshot> groupsPosts = [];
   List allPosts = [];

   QuerySnapshot snapshot = await usersGroupsRef
       .document(currentUser.id)
       .collection("usersGroups")
       .getDocuments();

   snapshot.documents.forEach((element) {
     groupIDs.add(element.documentID.toString());
   });
   print(groupIDs);

     groupIDs.forEach((data) async {
       groupsPosts.add(await groupPostsRef
           .document(data)
           .collection("groupPosts")
           .getDocuments());
       print(groupsPosts);
     });


   print(groupsPosts);

   groupsPosts.forEach((data) {
     allPosts.add(data.documents);
   });
   print(allPosts);

   List<Post> posts = allPosts.map((doc) => Post.fromDocument(doc)).toList();

   setState(() {
     groupPosts = posts;
   });
 }

I/flutter (11768): [1de5aec6-612e-41e8-90b2-04781b2a2954, 3545784b-0fca-4d35-bd0d-5d877e58808f, 66036190-304f-4984-9e7a-1a9a92e83466]
I/flutter (11768): []
I/flutter (11768): []
I/flutter (11768): [Instance of 'QuerySnapshot']
I/flutter (11768): [Instance of 'QuerySnapshot', Instance of 'QuerySnapshot']
I/flutter (11768): [Instance of 'QuerySnapshot', Instance of 'QuerySnapshot', Instance of 'QuerySnapshot']

Answer 1

forEach 不等待返回的期货。而是使用 Future.wait:

groupPosts.addAll(
  await Future.wait(
    groupIDs.map(
      (data) => groupPostsRef
          .document(data)
          .collection("groupPosts")
          .getDocuments(),
    ),
  ),
);

Flutter Firestore 异步函数/等待结果

1 个答案: