Question

在MyHomePage状态窗口小部件中，我有一个DropDownButton和一个ListView。我正在尝试根据选定的DropDownMenuItem重建ListView。但是，我在填充ListView时遇到问题。我必须转到另一个视图，然后返回MyHomePage以显示数据。

MyHomePageState：

class _MyHomePageState extends State<MyHomePage> {
 final List<String> _dow = [
  'Monday', 'Tuesday', 'Wednesday', 'Thursday', 'Friday', 'Saturday', 'Sunday'
 ].toList();

 @override
 void initState() {
  selectedDow = _dow.first;
  super.initState();
}

 @override
 Widget build(BuildContext context) {
  final _dowOptions = _dow.map((String day) =>
  new DropdownMenuItem(value: day, child: new Text(day))).toList();

  return new Scaffold(
   appBar: new AppBar(
    title: new DropdownButton(
        value: selectedDow, items: _dowOptions, onChanged: (s) {
      setState(() {
        selectedDow = s;
      }
      );
    }),
    actions: <Widget>[
      new IconButton(icon: new Icon(Icons.edit), onPressed: () {}),
      new IconButton(icon: new Icon(Icons.add), onPressed: () {
        newItem();
      })
    ],
  ),
  body: new DisplayList(),
  floatingActionButton: new FloatingActionButton(
      child: new Icon(Icons.add), onPressed: editItem),
);
}
}

显示列表：

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

 @override
 _DisplayListState createState() => new _DisplayListState();
}

class _DisplayListState extends State<DisplayList> {

 List<DataModel> dowList = new List<DataModel>();
 String currentCollection = selectedDow.toLowerCase();

 @override
 void initState() {
  updateList();
  super.initState();
}

 updateList() {
  Firestore.instance
    .collection(currentCollection)
    .snapshots
    .listen((snapshot) {
   for (var doc in snapshot.documents) {
    Firestore.instance.collection(doc['colPath'])
        .document(doc['docId'])
        .get()
        .then((docSnap) {
      String docId = docSnap.documentID;
      String docTitle = docSnap.data['title'];
      DataModel wData = new DataModel(
          docId, docTitle, null);
      dowList.add(wData);
    });
  }
});
}

 @override
 Widget build(BuildContext context) {
  return new ListView(
   children: dowList.map((DataModel item) {
    return new ListTile(
      title: new Text(item.title),
    );
  }).toList(),
);
}
}

提前感谢您的任何建议！

Answer 1

您的听众未通知您StatefulWidget州已更改。您可以通过将列表修改放入setState：

来修复它

setState(() { dowList.add(wData); });

但是，使用StreamBuilder可能会更好; Firestore提供了一个与其一起使用的流并处理所有更新。所以，无论你通常放置new DisplayList()，你都会把它放在...... {/ p>

new StreamBuilder(
  stream: Firestore.instance.collection(currentCollection).snapshots,
  builder: (BuildContext context, AsyncSnapshot<QuerySnapshot> snapshot) {
    if (!snapshot.hasData) return new Text('Loading...');
    return new ListView(
      children: [... build your list items here ...],
    );
  },
);

当另一个小部件的状态发生变化时重建小部件

1 个答案: