滚动浏览从网络上获取的数据

Question

我到了论坛，这是一个使用固定数据（字符串变量）滚动（Flutter）的例程。我希望数据是从Web（API Rest）检索的变量。恢复数据不是问题。我的问题是更改ListView的变量。

尝试时出现错误：“在小部件树中检测到重复的GlobalKey”。

此后，该应用将取消而不显示数据。

     body: NotificationListener(
        onNotification: (notif) {
          if (notif is ScrollEndNotification && scroll) {
            Timer(Duration(seconds: 1), () {
              _scroll();
            });
          }

          return true;
        },
        child: SingleChildScrollView(
          controller: _scrollController,
          child: Text(
            val, // <------------------------ here's the variable
            maxLines: 1000,
          ),
        ),
      ),

使用固定文本，该例程运行良好。 我只需要将字符串变量交换为ListView。 这是完整的原始代码。

import 'package:scroll/models/song.dart';
import 'package:flutter/material.dart';
import 'package:scroll/global.dart';
import 'package:shared_preferences/shared_preferences.dart';
import 'package:http/http.dart' as http;
import 'dart:async';
import 'dart:convert';

List<Song> _songLines = [];
void main() => runApp(MyApp());

class MyApp extends StatelessWidget {
  // This widget is the root of your application.
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        primarySwatch: Colors.blue,
      ),
      home: MyHomePage(),
    );
  }
}

class MyHomePage extends StatefulWidget {
  @override
  _MyHomePageState createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> with TickerProviderStateMixin {
  ScrollController _scrollController = ScrollController();
  bool scroll = false;
  int speedFactor = 20;

  int userId = 0;
  // Get json result and convert it to model. Then add
  Future<Null> getDetails() async {
    var _sharedPreferences = await SharedPreferences.getInstance();
    userId = _sharedPreferences.getInt('USERID') ?? 0;
    final String url = '$URL_SONGS/readOne.php?id=${562}'; // prov

    final mapResponse = await http.get(url);
    final responseJson = json.decode(mapResponse.body);

    setState(() {
      if (responseJson["result"] == "ok") {
        for (Map song in responseJson["data"]) {
          _songLines.add(Song.fromJson(song));
        }
      }
    });
  }

  _scroll() {
    double maxExtent = _scrollController.position.maxScrollExtent;
    double distanceDifference = maxExtent - _scrollController.offset;
    double durationDouble = distanceDifference / speedFactor;

    _scrollController.animateTo(_scrollController.position.maxScrollExtent,
        duration: Duration(seconds: durationDouble.toInt()),
        curve: Curves.linear);
  }

  _toggleScrolling() {
    setState(() {
      scroll = !scroll;
    });

    if (scroll) {
      _scroll();
    } else {
      _scrollController.animateTo(_scrollController.offset,
          duration: Duration(seconds: 1), curve: Curves.linear);
    }
  }

  @override
  Widget build(BuildContext context) {
    String val = '''
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''';
    return Scaffold(
      appBar: AppBar(
        title: Text('Lyrics'),
        actions: <Widget>[
          IconButton(
            icon: Icon(Icons.arrow_back),
            onPressed: (){
              speedFactor -= 20;
              _scroll();
            },
          ),
          IconButton(
            icon: Icon(Icons.arrow_forward),
            onPressed: (){
              speedFactor += 20;
              _scroll();
            },
          ),
        ],
      ),
      body: NotificationListener(
        onNotification: (notif) {
          if (notif is ScrollEndNotification && scroll) {
            Timer(Duration(seconds: 1), () {
              _scroll();
            });
          }

          return true;
        },
        child: SingleChildScrollView(
          controller: _scrollController,
          child: Text(
            val,
            maxLines: 1000,
          ),
        ),
      ),
      floatingActionButton: FloatingActionButton(onPressed: () {
        _toggleScrolling();
      }), // This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}