sqlite - 如何从数据库初始化列表(sqflite)

Question

我得到了sqflite函数Future<List<Sentence>>返回的getSentences(句子是具有int id和String句子的类)。现在我要在我的主窗口小部件树中列出该列表。因此，我创建了此功能:

 Future<void> initializeSentences() async {
    sentences = await getSentences();
  }

而且它严重地满足了我的需求。当执行该函数时，我的列表sentences充满了数据库中的句子。但是问题是，我不知道在哪里调用该函数。
我已经在initState()及以下Widget build(BuildContext context) {中尝试过它，但是如果我启动该应用程序，则总是需要做一些触发setState()的操作才能查看加载的列表。
如何在应用程序开始时初始化该列表，并显示该列表？

Answer 1

如果您使用Stateless小部件，则应通过以下构造函数初始化值。

class MyApp extends StatelessWidget {
  final List<String> sentences;

  const MyApp({Key key, this.sentences}) : super(key: key);
  @override
  Widget build(BuildContext context) {
    return Container(
      child: Column(
        children: [Text(sentences[0]), Text(sentences[1])],
      ),
    );
  }
}

如果您使用的是StatefullWidget，则应通过initState()方法进行初始化，或者使用如下所示的FutureBuilder()。

class MyApp extends StatelessWidget {
  static const String _title = 'Flutter Code Sample';

  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: _title,
      home: MyStatefulWidget(),
    );
  }
}

class MyStatefulWidget extends StatefulWidget {
  MyStatefulWidget({Key key}) : super(key: key);

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

class _MyStatefulWidgetState extends State<MyStatefulWidget> {
  Future<String> _calculation = Future<String>.delayed(
    Duration(seconds: 2),
    () => 'Data Loaded',
  );

  Widget build(BuildContext context) {
    return DefaultTextStyle(
      style: Theme.of(context).textTheme.headline2,
      textAlign: TextAlign.center,
      child: FutureBuilder<String>(
        future: _calculation, // a previously-obtained Future<String> or null
        builder: (BuildContext context, AsyncSnapshot<String> snapshot) {
          List<Widget> children;
          if (snapshot.hasData) {
            children = <Widget>[
              Icon(
                Icons.check_circle_outline,
                color: Colors.green,
                size: 60,
              ),
              Padding(
                padding: const EdgeInsets.only(top: 16),
                child: Text('Result: ${snapshot.data}'),
              )
            ];
          } else if (snapshot.hasError) {
            children = <Widget>[
              Icon(
                Icons.error_outline,
                color: Colors.red,
                size: 60,
              ),
              Padding(
                padding: const EdgeInsets.only(top: 16),
                child: Text('Error: ${snapshot.error}'),
              )
            ];
          } else {
            children = <Widget>[
              SizedBox(
                child: CircularProgressIndicator(),
                width: 60,
                height: 60,
              ),
              const Padding(
                padding: EdgeInsets.only(top: 16),
                child: Text('Awaiting result...'),
              )
            ];
          }
          return Center(
            child: Column(
              mainAxisAlignment: MainAxisAlignment.center,
              crossAxisAlignment: CrossAxisAlignment.center,
              children: children,
            ),
          );
        },
      ),
    );
  }
}