我如何修改代码以获得 Stream<dynamic> 为 stream 生成器键入 stream？</dynamic>

Question

Inside Stream builder, it is asking me to put Stream<builder> otherwise throwing an error,

type 'Future<dynamic>' is not a subtype of type 'Stream<dynamic>'

Now since I was following this answer , i had to code the stream something like this,

getGroupsOfUser() async {
    String _userID = await _getUID();
    DocumentSnapshot userInfo = await userCollection.document(_userID).get();
    return groupCollection.where(FieldPath.documentId, whereIn: userInfo.data['groups']).snapshots();
  }

Now I know maybe if I could overcome using async I may fix it but I need to get the uid and the array of groups which is an async function and I can't really assign them as variables otherwise I'm getting the error only static members can be accessed in initializers

Please, someone, help me I am very beginner in this.

Answer 1

The error must be from the line

return groupCollection.where(FieldPath.documentId, whereIn: userInfo.data['groups']).snapshots();

Because.snapshots() method returns a Stream instead of a Future, and since your getGroupsOfUser() is a Future, it is throwing an error that you cannot return a Stream from a function that returns a Future.

My solution: 1 - Put the logic for getting the userID and the userInfo inside the initState() ie make a Future for it. 2 - Seperate the last line from the Future and wrap it with a StreamBuilder after successfully getting the userinfo from step 1.

Answer 2

getGroupsOfUser() should return a Stream since snapshots() returns a Stream . Therefore you need to do the following:

Stream<QuerySnapshot> getGroupsOfUser() async* {
    String _userID = await _getUID();
    DocumentSnapshot userInfo = await userCollection.document(_userID).get();
    yield* groupCollection.where(FieldPath.documentId, whereIn: userInfo.data['groups']).snapshots();
  }

Since you need to return a stream then you need to use async* and use the yield* keyword to return.