反映克隆应用程序Firebase数据库连接不起作用

Question

这是反省克隆应用程序的摘录。我正确遵循了Firebase的说明，但是卡（firebase数据库中的“故事”）不会显示。我不确定Gradle文件或pubspec.yaml之一是否有错误。

此外，该应用程序测试可在iOS模拟器中成功运行，但不适用于Android模拟器。

import 'package:flutter/material.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'dart:async';

void main() => runApp(MyApp());

class MyApp extends StatelessWidget {

  @override
  Widget build(BuildContext context) {

    return MaterialApp(
      home: Scaffold(body: FirestoreSlideshow())
    );
  }
}

class FirestoreSlideshow extends StatefulWidget {
  createState() => FirestoreSlideshowState();
}

class FirestoreSlideshowState extends State<FirestoreSlideshow> {

  final PageController ctrl = PageController(viewportFraction: 0.8);

  final Firestore db = Firestore.instance;
  Stream slides;


  String activeTag = 'favorites';

  // Keep track of current page to avoid unnecessary renders
  int currentPage = 0;


  @override
  void initState() {
    _queryDb();

    // Set state when page changes
    ctrl.addListener(() { 
      int next = ctrl.page.round();

      if(currentPage != next) { 
        setState(() {
          currentPage = next;
        });
      } 
    });
  }

  @override
  Widget build(BuildContext context) { 
      return StreamBuilder(
          stream: slides,
          initialData: [],
          builder: (context, AsyncSnapshot snap) { 

            List slideList = snap.data.toList();

            return PageView.builder(

              controller: ctrl,
              itemCount: slideList.length + 1,
              itemBuilder: (context, int currentIdx) {


              if (currentIdx == 0) {
                return _buildTagPage();
              } else if (slideList.length >= currentIdx) {
                // Active page
                bool active = currentIdx == currentPage;
                return _buildStoryPage(slideList[currentIdx - 1], active);
              }
              return Text('No slide available');
            }
          );
        }
    );
  }

  void _queryDb({ String tag ='favorites' }) {

    // Make a Query
    Query query = db.collection('stories').where('tags', arrayContains: tag);

    // Map the documents to the data payload
    slides = query.snapshots().map((list) => list.documents.map((doc) => doc.data));

    // Update the active tag
    setState(() {
      activeTag = tag;
    });

  }


  // Builder Functions

  _buildStoryPage(Map data, bool active) {
     // Animated Properties
    final double blur = active ? 30 : 0;
    final double offset = active ? 20 : 0;
    final double top = active ? 100 : 200;


    return AnimatedContainer(
      duration: Duration(milliseconds: 500),
      curve: Curves.easeOutQuint,
      margin: EdgeInsets.only(top: top, bottom: 50, right: 30),
      decoration: BoxDecoration(
        borderRadius: BorderRadius.circular(20),

        image: DecorationImage(
            fit: BoxFit.cover,
            image: NetworkImage(data['img']),
        ),

        boxShadow: [BoxShadow(color: Colors.black87, blurRadius: blur, offset: Offset(offset, offset))]
      ),
      child: Center(
          child: Text(data['title'], style: TextStyle(fontSize: 40, color: Colors.white))
        )
    );
  }


  _buildTagPage() {
    return Container(child: 
      Column(
        mainAxisAlignment: MainAxisAlignment.center,
        crossAxisAlignment: CrossAxisAlignment.start,

        children: [
          Text('Your Stories', style: TextStyle(fontSize: 40, fontWeight: FontWeight.bold),),
          Text('FILTER', style: TextStyle( color: Colors.black26 )),
          _buildButton('favorites'),
          _buildButton('happy'),
          _buildButton('sad')
        ],
      )
    );
  }

  _buildButton(tag) {
    Color color = tag == activeTag ? Colors.purple : Colors.white;
    return FlatButton(color: color, child: Text('#$tag'), onPressed: () => _queryDb(tag: tag));
  }
}