firebase - 无法从数据库获取DataSnapshot并获取空值

Question

我试图通过按用户的故事按钮来查看用户故事，将我导航到整页的StoryView以查看图像。我认为我无法将数据传递到下一页或从数据库查询数据。我不确定哪里出了问题。
这是我得到的错误:

The following _TypeError was thrown building Builder: type '(DataSnapshot) => Null' is not a subtype of type '(dynamic) => dynamic' of 'f''

这是我在要查看图像的实际页面上调用要检索的数据的地方。错误指向crudMethods.getStoryListData()行

import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:firebase_database/firebase_database.dart';
import 'package:flutter/material.dart';
import 'package:link_me/services/crud.dart';
import "package:story_view/story_view.dart";

class StoryPageView extends StatefulWidget {
  final String currentUser;
  final String storyUrl;

  StoryPageView({this.currentUser, this.storyUrl});

  @override
  _StoryPageViewState createState() => _StoryPageViewState();
}

class _StoryPageViewState extends State<StoryPageView> {
  CrudMethods crudMethods = new CrudMethods();
  List<String> itemList = new List();
  final StoryController controller = StoryController();
  

  QuerySnapshot storySnapshot;

  @override
  void initState() {
    super.initState();
    CrudMethods crudMethods = new CrudMethods();

    crudMethods.getStoryListData().then((DataSnapshot snapshot) {
      //storySnapshot = result;
      var urlData = snapshot.value;
      //itemList.clear();
      urlData.forEach((key, value) {
        itemList.add(value['storyUrl']);
      });

      setState(() {
        print(itemList.length);
      });
    });
  }

 loadStory() {
    return ListView(
      children: <Widget>[
        itemList == null ? CircularProgressIndicator()
        : Container(
          child: StoryView(
             storyItems: [
              for (var i in itemList) show(i)
            ], 
            controller: controller,
            progressPosition: ProgressPosition.top,
            repeat: false,
            ),
        ),
      ],
    );
  }

  show(String urlData) {
    return StoryItem.pageImage(
      url: urlData, 
      controller: controller,
      );
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Container(
        margin: EdgeInsets.all(8.0),
        child: Column(
          children:<Widget>[
            Padding(
              padding: EdgeInsets.fromLTRB(0, 5, 5, 5),
              child: Container(
                height: MediaQuery.of(context).size.width,
                width: MediaQuery.of(context).size.height,
                child: loadStory(),
              ),
            ),
          ],
        ),
      ),
    );
  }
}

这就是我从主故事列表页面导航到该页面的方式，该页面显示了发布新故事的所有用户

onTap: () => Navigator.push(context,
                  MaterialPageRoute(builder: (context) => StoryPageView(currentUser: currentUser.id,))),

这是从我用来调用数据的实用程序文件中获得的

getStoryListData() async {
    return storyPostReference.document(currentUser.id).collection("storyPostItems").orderBy("timestamp", descending: true).snapshots();
  }

Answer 1

您正在UI中使用Future，但是从getStoryListData()返回流，因此您必须以
future 的getStoryListData()异步{
Querysnapshot快照= storyPostReference.document(currentUser.id).collection(“storyPostItems”)。orderBy(“timestamp”，降序:true)。得到();
返回快照；