颤振网格视图值未更新

Question

在我的flutter应用程序中，我将GridView与firebase一起使用.firebase的值正在获取。在状态类initState中编写firebase值检索。我声明了一个变量document。我想要createchildwidget()中的详细信息值。但是在createchildwidget()中显示为null。如何在dertails函数中检索createchildwidget()。请帮助我。

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

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

  class MyApp extends StatelessWidget {
    // This widget is the root of your application.

    MyApp({this.firestore});
    final Firestore firestore;


    @override
    Widget build(BuildContext context) {
      return MaterialApp(
          home: MyHomePage(title: 'My Shop', firestore: firestore)
      );
    }
  }

  class MyHomePage extends StatefulWidget {

    MyHomePage({Key key, this.title, this.firestore}) : super(key: key);
    final Firestore firestore;
    final String title;

    @override
    _MyHomePageState createState() => new _MyHomePageState(firestore: firestore);
  }

  class _MyHomePageState extends State<MyHomePage> {
    _MyHomePageState({this.firestore});
    final Firestore firestore;
    var details = [];

    void initState(){
      super.initState();
      Firestore.instance.collection("names").getDocuments().then((data) async{
        var list = data.documents;
        details = list;
        print("init state document:"+details.length.toString());  // value is getting

        setState((){
          details = list;
        });
      });



    }

    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: new AppBar(
          iconTheme: IconThemeData(
            color: Colors.black, //change font color here
          ),
          backgroundColor: new Color(0xFFFAFAFA),
        )
        title:"title",
        body: TheGridview().build(),
      );
    }
  }

  class GridviewClass extends _MyHomePageState{
    Card addGridCell(String name, IconData icon){
      return Card(
        elevation: 1.0,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          mainAxisSize: MainAxisSize.min,
          verticalDirection: VerticalDirection.down,
          children: <Widget>[
            Center(child: Icon(icon)),
            Text(name)
          ],
        ),
      );
    }

    @override
    Widget build(BuildContext context) {
      return GridView.count(
        primary: true,
        padding: EdgeInsets.all(1.0),
        crossAxisCount: 2,
        childAspectRatio: 1.0,
        mainAxisSpacing: 1.0,
        crossAxisSpacing: 1.0,

        children: createchildwidget(),

        /*  children: <Widget>[
              addGridCell("Home", Icons.access_alarm)
            ],*/


      );
    }

    List<Widget> createchildwidget(){
      print("createchildwidget:"+details.length.toString()); // the value getting 0
      List<Widget> createchildwidget = List<Widget>();
      for(int i=0;i<details.length;i++){
        createchildwidget.add(GridviewClass().addGridCell(details[i].data['message'], Icons.access_alarm));

        }
            return createchildwidget;
        }


  }

Answer 1

我从下面的代码解决了这个问题。我将类createchildwidget更改为函数并用_MyHomePageState

编写

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

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

  class MyApp extends StatelessWidget {
    // This widget is the root of your application.

    MyApp({this.firestore});
    final Firestore firestore;


    @override
    Widget build(BuildContext context) {
      return MaterialApp(
          home: MyHomePage(title: 'My Shop', firestore: firestore)
      );
    }
  }

  class MyHomePage extends StatefulWidget {

    MyHomePage({Key key, this.title, this.firestore}) : super(key: key);
    final Firestore firestore;
    final String title;

    @override
    _MyHomePageState createState() => new _MyHomePageState(firestore: firestore);
  }

  class _MyHomePageState extends State<MyHomePage> {
    _MyHomePageState({this.firestore});
    final Firestore firestore;

    var documents = [];
    bool isDocLoaded=false;


    void initState() {
      Firestore.instance.collection("messages").getDocuments().then((data) async {
        var list = data.documents;
        documents = list;
        print("init state document:" +
            documents.length.toString()); // value is getting
        super.initState();
        setState(() {
          isDocLoaded = true;
          documents = list;
        });
      });
    }

    @override
    Widget build(BuildContext context) {
      return new Scaffold(
        appBar: new AppBar(
          iconTheme: IconThemeData(
            color: Colors.black, //change font color here
          ),
          backgroundColor: new Color(0xFFFAFAFA),
        )
        title:"title",
        body: isDocLoaded? TheGridview():Center(child:CircularProgressIndicator()),
      );
    }

    Widget TheGridView(){
      return GridView.count(
        primary: true,
        padding: EdgeInsets.all(1.0),
        crossAxisCount: 2,
        childAspectRatio: 1.0,
        mainAxisSpacing: 1.0,
        crossAxisSpacing: 1.0,

        children: createChildrenTexts(),

        /*  children: <Widget>[
              makeGridCell("Home", Icons.access_alarm)
            ],*/
      );
    }

    Card makeGridCell(String name, IconData icon){
      return Card(
        elevation: 1.0,
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          mainAxisSize: MainAxisSize.min,
          verticalDirection: VerticalDirection.down,
          children: <Widget>[
            Center(child: Icon(icon)),
            Text(name)
          ],
        ),
      );
    }
    List<Widget> createChildrenTexts(){
      print("createChildrenTexts:"+documents.length.toString()); // the value getting 0
      List<Widget> childrenTexts = List<Widget>();
      for(int i=0;i<documents.length;i++){
        childrenTexts.add(makeGridCell(makeGridCell(data[i].data['message'], Icons.access_alarm));
        }
            return createchildwidget;
        }
  }