Question

我正在尝试构建一个简单的报价Flutter应用程序，在其中显示报价列表并允许用户“喜欢”报价。我正在为此使用Streambuilder。我的问题是，即使我最多有50个引号，Firestore的使用情况仪表板仍显示大量读取（每个用户近300个）。我有一种预感，我的代码中的某些内容导致Streambuilder多次触发（也许用户“喜欢”引号），并且Streambuilder正在加载所有引号，而不是仅加载用户视口中的引号。对于如何解决此问题以减少读取次数的任何帮助，将不胜感激。

import 'dart:convert';
import 'dart:math';

import 'package:flutter/material.dart';
import 'package:positivoapp/utilities.dart';
import 'package:cloud_firestore/cloud_firestore.dart';
import 'package:share/share.dart';


class QuotesScreen extends StatefulWidget {
  @override
  QuotesScreenLayout createState() => QuotesScreenLayout();
}

class QuotesScreenLayout extends State<QuotesScreen> {
  List<String> quoteLikeList = new List<String>();

  // Get Goals from SharedPrefs
  @override
  void initState() {
    super.initState();
    getQuoteLikeList();
  }

  Future getQuoteLikeList() async {
    if (Globals.globalSharedPreferences.getString('quoteLikeList') == null) {
      print("No quotes liked yet");
      return;
    }

    String quoteLikeListString =
    Globals.globalSharedPreferences.getString('quoteLikeList');
    quoteLikeList = List.from(json.decode(quoteLikeListString));
    setState(() {});
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      body: Center(
        child: Container(
            padding: const EdgeInsets.all(10.0),
            child: StreamBuilder<QuerySnapshot>(
              stream: Firestore.instance
                  .collection(FireStoreCollections.QUOTES)
                  .orderBy('timestamp', descending: true)
                  .snapshots(),
              builder: (BuildContext context,
                  AsyncSnapshot<QuerySnapshot> snapshot) {
                if (snapshot.hasError)
                  return new Text('Error: ${snapshot.error}');
                switch (snapshot.connectionState) {
                  case ConnectionState.waiting:
                    return Row(
                      mainAxisSize: MainAxisSize.min,
                      children: [
                        new CircularProgressIndicator(),
                        new Text("Loading..."),
                      ],
                    );
                  default:
                    print('Loading Quotes Stream');
                    return new ListView(
                      children: snapshot.data.documents
                          .map((DocumentSnapshot document) {
                        return new QuoteCard(
                          quote:
                              Quote.fromMap(document.data, document.documentID),
                          quoteLikeList: quoteLikeList,
                        );
                      }).toList(),
                    );
                }
              },
            )),
      ),
    );
  }
}

class QuoteCard extends StatelessWidget {
  Quote quote;
  final _random = new Random();
  List<String> quoteLikeList;

  QuoteCard({@required this.quote, @required this.quoteLikeList});

  @override
  Widget build(BuildContext context) {
    bool isLiked = false;
    String likeText = 'LIKE';
    IconData icon = Icons.favorite_border;
    if (quoteLikeList.contains(quote.quoteid)) {
      icon = Icons.favorite;
      likeText = 'LIKED';
      isLiked = true;
    }

    return Center(
      child: Card(
        child: Column(
          mainAxisSize: MainAxisSize.min,
          crossAxisAlignment: CrossAxisAlignment.start,
          children: <Widget>[
            Container(
              constraints: new BoxConstraints.expand(
                height: 350.0,
                width: 400,
              ),
              child: Stack(children: <Widget>[
                Container(
                  decoration: BoxDecoration(
                    image: DecorationImage(
                      colorFilter: new ColorFilter.mode(
                          Colors.black.withOpacity(0.25), BlendMode.darken),
                      image: AssetImage('images/${quote.imageName}'),
                      fit: BoxFit.cover,
                    ),
                  ),
                ),
                Center(
                  child: Padding(
                    padding: const EdgeInsets.all(15.0),
                    child: Text(
                      quote.quote,
                      textAlign: TextAlign.center,
                      style: TextStyle(
                          fontSize: 30.0,
                          fontFamily: 'bold',
                          fontWeight: FontWeight.bold,
                          color: Color.fromRGBO(255, 255, 255, 1)),
                    ),
                  ),
                ),
              ]),
            ),
            Padding(
              padding: EdgeInsets.fromLTRB(18, 10, 10, 0),
              child: Text(
                'Liked by ${quote.numLikes} happy people',
                textAlign: TextAlign.left,
                style: TextStyle(
                    fontFamily: 'bold',
                    fontWeight: FontWeight.bold,
                    color: Colors.black),
              ),
            ),
            ButtonBar(
              alignment: MainAxisAlignment.start,
              children: <Widget>[
                FlatButton(
                  child: UtilityFunctions.buildButtonRow(Colors.red, icon, likeText),
                  onPressed: () async {
                    // User likes / dislikes this quote, do 3 things
                    // 1. Save like list to local storage
                    // 2. Update Like number in Firestore
                    // 3. Toggle isLiked
                    // 4. Setstate - No need

                    // Check if the quote went from liked to unlike or vice versa

                    if (isLiked == false) {
                      // False -> True, increment, add to list
                      quoteLikeList.add(quote.quoteid);

                      Firestore.instance
                          .collection(FireStoreCollections.QUOTES)
                          .document(quote.documentID)
                          .updateData({'likes': FieldValue.increment(1)});

                      isLiked = true;
                    } else {
                      // True -> False, decrement, remove from list
                      Firestore.instance
                          .collection(FireStoreCollections.QUOTES)
                          .document(quote.documentID)
                          .updateData({'likes': FieldValue.increment(-1)});
                      quoteLikeList.remove(quote.quoteid);

                      isLiked = false;
                    }

                    // Write to local storage
                    String quoteLikeListJson = json.encode(quoteLikeList);
                    print('Size of write: ${quoteLikeListJson.length}');
                    Globals.globalSharedPreferences.setString(
                        'quoteLikeList', quoteLikeListJson);

                    // Guess setState(); will happen via StreamBuilder - Yes
//                    setState(() {});
                  },
                ),
              ],
            ),
          ],
        ),
      ),
    );
  }
}

Answer 1

您的直觉是正确的。由于Streambuilder在Build方法中，因此每次重新构建窗口小部件树时，都会在Firestore上进行读取。这比我能here解释得更好。

为防止这种情况发生，您应该在initState方法中侦听Firestore流。这样，它将仅被调用一次。像这样：

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>{% block title %}{% endblock %}</title>
    {% block styles %}

    {% endblock %}
    <link rel="stylesheet" type="stylesheet" href="main_styles.css">
    <link rel="stylesheet" href="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/css/bootstrap.min.css" integrity="sha384-9aIt2nRpC12Uk9gS9baDl411NQApFmC26EwAOH8WgZl5MYYxFfc+NcPb1dKGj7Sk" crossorigin="anonymous">
</head>
<body>
    <nav class="navbar navbar-expand-lg navbar-light bg-light">
      <a class="navbar-brand" href="#">Navbar</a>
      <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
      </button>

      <div class="collapse navbar-collapse" id="navbarSupportedContent">
        <ul class="navbar-nav mr-auto">
          <li class="nav-item active">
            <a class="nav-link" href="#">Home <span class="sr-only">(current)</span></a>
          </li>
          <li class="nav-item">
            <a class="nav-link" href="#">Link</a>
          </li>
          <li class="nav-item dropdown">
            <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
              Dropdown
            </a>
            <div class="dropdown-menu" aria-labelledby="navbarDropdown">
              <a class="dropdown-item" href="#">Action</a>
              <a class="dropdown-item" href="#">Another action</a>
              <div class="dropdown-divider"></div>
              <a class="dropdown-item" href="#">Something else here</a>
            </div>
          </li>
          <li class="nav-item">
            <a class="nav-link disabled" href="#" tabindex="-1" aria-disabled="true">Disabled</a>
          </li>
        </ul>
        <form class="form-inline my-2 my-lg-0">
          <input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
          <button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
        </form>
      </div>
    </nav>

    {% block content %}
    {% endblock %}

    <script src="https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity="sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C+OGpamoFVy38MVBnE+IbbVYUew+OrCXaRkfj" crossorigin="anonymous"></script>
    <script src="https://cdn.jsdelivr.net/npm/popper.js@1.16.0/dist/umd/popper.min.js" integrity="sha384-Q6E9RHvbIyZFJoft+2mJbHaEWldlvI9IOYy5n3zV9zzTtmI3UksdQRVvoxMfooAo" crossorigin="anonymous"></script>
    <script src="https://stackpath.bootstrapcdn.com/bootstrap/4.5.0/js/bootstrap.min.js" integrity="sha384-OgVRvuATP1z7JjHLkuOU7Xw704+h835Lr+6QL9UvYjZE3Ipu6Tp75j7Bh/kR0JKI" crossorigin="anonymous"></script>
</body>
</html>

Flutter：Streambuilder导致Firestore读取过多

1 个答案: