带有两个模拟器的 StreamBuilder 数据

Question

当我打开两个模拟器时，我遇到了奇怪的（据我所知）StreamListener 数据行为。

我有一段代码可以在 ListView 中读取 Firebase 的 RealtimeDB 和 return。

body: StreamBuilder(
    stream: _database.onValue,
    builder: (context, snapshot) {
      List<FirstRoundQuestion> frqList = [];
      if (snapshot.hasData) {
        final firstRoundQuestion = Map<dynamic, dynamic>.from(
            (snapshot.data! as DatabaseEvent).snapshot.value
                as Map<dynamic, dynamic>);
        firstRoundQuestion.forEach((key, value) {
          final frq = Map<String, dynamic>.from(value);
          frqList.add(FirstRoundQuestion(
              question: frq['question'],
              answer: frq['answer'],
              answered: frq['answered']));
        });
        return ListView.builder(
          reverse: true,
          physics: NeverScrollableScrollPhysics(),
          controller: _controller.pageController,
          itemCount: frqList.length,
          itemBuilder: (context, index) {
            return Row(
              children: [
                Text('${frqList[index].question}'),
                TextButton(
                    onPressed: ()  {}
                          
                    child: Text('${frqList[index].answered}'))
              ],
            );
          },
        );
      } else {
        return Text("Doesn't work");
      }
    }));

在移动模拟器上构建应用程序然后在边缘模拟器上构建应用程序时，我得到的是此列表的两个不同顺序，第一个是升序，另一个是降序。伙计们，我在这里想念什么？ :o

希望我解释清楚了。

Answer 1

要按特定顺序显示项目，您需要做两件事：

从数据库中按该顺序检索项目。
然后按照您在代码中收到它们的顺序处理它们。

如果您还没有从数据库中请求特定顺序的项目，例如您可以这样做：

body: StreamBuilder(
  stream: _database.orderByKey().onValue,
  ...

一旦您按特定顺序请求项目，您构建器中的这段代码无法按顺序处理项目：

if (snapshot.hasData) {
  final firstRoundQuestion = Map<dynamic, dynamic>.from(
      (snapshot.data! as DatabaseEvent).snapshot.value
          as Map<dynamic, dynamic>);
  firstRoundQuestion.forEach((key, value) {
    final frq = Map<String, dynamic>.from(value);
    frqList.add(FirstRoundQuestion(
        question: frq['question'],
        answer: frq['answer'],
        answered: frq['answered']));
  });

地图中项目的顺序未定义，因此当您将快照的整个值转换为地图时，您将失去项目的顺序。

按顺序处理项目的解决方案是循环快照的children 属性：

(snapshot.data! as DatabaseEvent).snapshot.children.forEach((snapshot) {
  final frq = Map<Sting, dynamic>.from(snapshot.value as Map<dynamic, dynamic>);
  frqList.add(FirstRoundQuestion(
      question: frq['question'],
      answer: frq['answer'],
      answered: frq['answered']));
})

带有两个模拟器的 StreamBuilder 数据

StreamBuilder data with two Emulators

firebase-realtime-database

flutter