Flutter - 如何在streambuilder中使用await？

我想在streambuilder 中使用await。但是，如果您在内部使用 async，则会出现错误。在下面的代码中！！！！！！这就是我想要解决的部分。如果我能告诉你如何做的话，非常感谢。

class _MemoStreamState extends State<MemoStream> {
final _fireStore = Firestore.instance;

@override
Widget build(BuildContext context) {
return StreamBuilder<QuerySnapshot>(
  stream: _fireStore
      .collection(widget.logInUsrEmail)
      .orderBy('id', descending: false)
      .snapshots(),
  builder: (context, AsyncSnapshot<QuerySnapshot> snapshot) {
    if (!snapshot.hasData) return LinearProgressIndicator();

    final memos = snapshot.data.documents;
    List<MemoMaterial> memoList = [];

    for (var memo in memos) {
      final memoDocumentID = memo.documentID;
      final memoTitle = await PlatformStringCryptor().decrypt(memo.data['title'], _key);  !!!!!!!!!!
      final memoUsrID = memo.data['usrID'];
      final memoUsrPW = memo.data['usrPW'];
      final memoText = memo.data['text'];
      final memoCreateTime = memo.data['createTime'];

      final memoMaterial = MemoMaterial(
        logInUsrEmail: widget.logInUsrEmail,
        doc: memoDocumentID,
        title: memoTitle,
        usrID: memoUsrID,
        usrPW: memoUsrPW,
        text: memoText,
        createTime: memoCreateTime,
      );
      memoList.add(memoMaterial);
    }

    return Expanded(
      child: new ListView.builder(

你应该做这样的事情：

  Stream<List<MemoMaterial>> memosStream;

  Future<MemoMaterial> generateMemoMaterial(Memo memo) async {
    final memoTitle =
        await PlatformStringCryptor().decrypt(memo.data['title'], _key);

    return MemoMaterial(
      logInUsrEmail: widget.logInUsrEmail,
      doc: memo.documentID,
      title: memoTitle,
      usrID: memo.data['usrID'],
      usrPW: memo.data['usrPW'],
      text: memo.data['text'];,
      createTime: memo.data['createTime'],
    );
  }

  @override
  void initState() {
    memosStream = _fireStore
            .collection(widget.logInUsrEmail)
            .orderBy('id', descending: false)
            .snapshots()
            .asyncMap((memos) => Future.wait([for (var memo in memos) generateMemoMaterial(memo)]));
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
  return StreamBuilder<List<MemoMaterial>>(
    stream: memosStream // Use memostream here

asyncMap()会将每组新的文档“转换”为 MemoMaterial 列表，并在执行操作时将该列表发送到流中。

Future.wait()允许同时执行多个异步请求。