Url 使用 Flutter/Dart 的启动器

Question

各位晚安，

我对 URL 启动器有一点小问题。 基本上，我想做的是从 Future function （从 API 检索）获取 URL （从 API 检索），然后在按下凸起的按钮 D 后导航到该 ZE6B391A8D2C4D45902A23A8B6585703。 我实现的代码有效，但并非没有一个小而讨厌的错误。 该错误出现大约半秒到一秒（我假设直到 API 返回 URL），然后将凸起的按钮绘制到屏幕上并且工作正常； 然后我可以导航到该站点。 我试图完全摆脱这个错误。 为了节省您一些时间，相关的 FutureBuilder 是第二个。 下面是我的代码：

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:url_launcher/url_launcher.dart';

import '../models/yahoo_finance_stock_info.dart';
import '../providers/companies_provider.dart';

class BusinessScreen extends StatefulWidget {
  static const routeName = '/business-screen';

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

class _BusinessScreenState extends State<BusinessScreen>
    with AutomaticKeepAliveClientMixin<BusinessScreen> {
  @override
  bool get wantKeepAlive => true;

  Future _companyDescription;
  Future _urlForUrlLauncher;

  var _isInit = true;

  @override
  void didChangeDependencies() {
    if (_isInit) {
      final companyTicker = ModalRoute.of(context).settings.arguments as String;
      final loadedCompany = Provider.of<Companies>(context, listen: false)
          .findByTicker(companyTicker);

      _companyDescription =
          Companies().getSecurityExtendStats(loadedCompany.tickerSymbol);

      _urlForUrlLauncher =
          Companies().getHistoricalData(loadedCompany.tickerSymbol);
    }
    _isInit = false;
    super.didChangeDependencies();
  }

  @override
  void initState() {
    // TODO: implement initState
    super.initState();
    _companyDescription;
  }

  @override
  Widget build(BuildContext context) {
    super.build(context);
    final companyTicker = ModalRoute.of(context).settings.arguments as String;
    final loadedCompany = Provider.of<Companies>(context, listen: false)
        .findByTicker(companyTicker);

    return Container(
      color: Colors.black87,
      child: Column(
        children: <Widget>[
          Container(
            height: 300,
            width: double.infinity,
            color: Colors.white,
            padding: EdgeInsets.all(10),
            child: SingleChildScrollView(
              padding: EdgeInsets.only(left: 15),
              scrollDirection: Axis.vertical,
              child: FutureBuilder<StockInformation>(
                future: _companyDescription,
                builder: (BuildContext context,
                    AsyncSnapshot<StockInformation> snapshot) {
                  if (snapshot.data != null) {
                    return Text(snapshot.data.assetProfile.longBusinessSummary);
                  }
                  return Container(
                    height: 300,
                    child: Center(
                      child: CircularProgressIndicator(),
                    ),
                  );
                },
              ),
            ),
          ),
          Container(
            height: 75,
            width: double.infinity,
            child: Center(
              child: FutureBuilder(
                future: _urlForUrlLauncher,
                builder: (BuildContext context, AsyncSnapshot snapshot) {
                  if (snapshot.data[0]['finalLink'] != null) {
                    String url10K = snapshot.data[0]['finalLink'];
                    return RaisedButton(
                      shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(10),
                        side: BorderSide(
                          color: Colors.grey,
                          width: 1,
                        ),
                      ),
                      onPressed: () async {
                        var url = url10K;
                        if (await canLaunch(url)) {
                          await launch(url);
                        } else {
                          throw 'Could not launch $url';
                        }
                      },
                      child: Text(
                        'Go to company\'s filings',
                        style: TextStyle(
                          color: Colors.white,
                        ),
                      ),
                    );
                  } else {
                    return RaisedButton(
                      shape: RoundedRectangleBorder(
                        borderRadius: BorderRadius.circular(10),
                        side: BorderSide(
                          color: Colors.grey,
                          width: 1,
                        ),
                      ),
                      onPressed: null,
                      child: Text(
                        'Go to company\'s filings',
                        style: TextStyle(color: Colors.white,),
                      ),
                    );
                  }
                },
              ),
            ),
          )
        ],
      ),
    );
  }
}

在此先感谢您提供有关此问题的所有帮助！

Answer 1

在第二个FutureBuilder中更改条件，

builder: (BuildContext context, AsyncSnapshot snapshot) {
  if (snapshot.data != null && snapshot.data[0]['finalLink'] != null) {
    // raised button with onpressed
  } else {
    // raised button with onpressed as null
  }
}