snapshot.hasData返回假

Question

我正在设置一个从API获取数据的应用程序。我想添加一个连接插件来检查用户是否有互联网连接。我不熟悉地图，所以我需要一些帮助

import 'dart:convert';
import 'dart:io';

import 'package:flutter/foundation.dart';
import 'package:flutter/material.dart';
import 'package:flutter_t/CONSTANTS.dart';
import 'package:flutter_t/Themes.dart';
import 'package:http/http.dart' as http;
import 'dart:async';
import 'package:connectivity/connectivity.dart';

final String baseurl = "http://xxx.xxx.xxx.xxx/api/v1";
final String imgurl = "http://xxx.xxx.xxx.xxx";



class Specializationgrid extends StatefulWidget {
  @override
  SpecializationgridState createState() => SpecializationgridState();
}

class SpecializationgridState extends State<Specializationgrid> {

  var _connectionStatus = 'Unknown';
  Connectivity connectivity;
  StreamSubscription<ConnectivityResult> subscription;


  List<dynamic> datas =[];


  @override
  void initState() {
    super.initState();
    connectivity = new Connectivity();
    subscription = connectivity.onConnectivityChanged
        .listen((ConnectivityResult result){

      if (result == ConnectivityResult.mobile || result == ConnectivityResult.wifi
      ) {
        setState(() {});
      }
    });


  }

  @override
  void dispose() {
    subscription.cancel();
    super.dispose();

  }


  Future<String> getSpecialData() async{

      var res = await http.get(Uri.encodeFull(baseurl+"/specialization"),headers: {"Accept": "application/json"});
      if (res.statusCode == HttpStatus.OK) {
        var result = json.decode(res.body);
        setState(() { });
       return result;
      }


//    return "Success!";

  }
  @override
  Widget build(BuildContext context) {

    var stateRoutes = ["await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),)"
        'await Navigator.push(context,new MaterialPageRoute( builder: (context) = labTest(),),),await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),'
        'await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),'
        'await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),'
        'await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),await Navigator.push(context,new MaterialPageRoute( builder: (context) = doctors(),),),'
       ];

    return Padding(
      padding: const EdgeInsets.symmetric(horizontal:15.0),
      child: FutureBuilder(
        future: getSpecialData(),
        builder: (context, snapshot){
          print('snapshot: $snapshot');
          if (snapshot.hasData)
            {
              var datas = snapshot.data;
              return new GridView.builder(
                gridDelegate: SliverGridDelegateWithFixedCrossAxisCount(crossAxisCount: 3,mainAxisSpacing: 0,crossAxisSpacing: 0),
                itemCount: datas == null ? 0 : datas.length,
                shrinkWrap: true,
                physics: const NeverScrollableScrollPhysics(),
                itemBuilder: (BuildContext context, int index){
                  return Container(
                    child: InkWell(
                        splashColor: Colors.pinkAccent,

                        child: Column(

                          crossAxisAlignment: CrossAxisAlignment.center,
                          mainAxisAlignment: MainAxisAlignment.center,
                          mainAxisSize: MainAxisSize.min,
                          children: <Widget>[

                            Card(
                              elevation: 0,
                              child: Container(

                                child: Image.network(imgurl +datas[index]['img'],width: 50,height: 50,),
                              ),
                            ),
                            Card(
                              elevation: 0,
                              child: Container(
                                child: Text(datas[index]['title'],style: specializationTextStyle,softWrap: true,),
                              ),
                            )
                          ],
                        ),
                        onTap: () async{
                          // ignore: unnecessary_statements
                          stateRoutes[index];

                          /* if(navigationResult == true)
                      {
                        return null;
                      }*/
                        }
                    ),
                  );
                },

              );
            }
          else
            {
              return Padding(
                padding: const EdgeInsets.symmetric(vertical: 100),
                child: Column(
                  mainAxisAlignment: MainAxisAlignment.center,
                  mainAxisSize: MainAxisSize.max,
                  children: <Widget>[
                    Center(
                      child: new CircularProgressIndicator(),
                    ),
                    SizedBox(height: 50,),
                    Text('No internet connectivity')
                  ],
                ),
              );
            }
        },

      ),
    );


    }

}



Flutter Doctor

jake@jake:~/Downloads/OpTicket$ flutter doctor -v
[✓] Flutter (Channel unknown, v1.2.1, on Linux, locale en_IN)
    • Flutter version 1.2.1 at /home/jake/Downloads/flutter
    • Framework revision 8661d8aecd (5 months ago), 2019-02-14 19:19:53 -0800
    • Engine revision 3757390fa4
    • Dart version 2.1.2 (build 2.1.2-dev.0.0 0a7dcf17eb)

[✓] Android toolchain - develop for Android devices (Android SDK version 28.0.3)
    • Android SDK at /home/jake/Android/Sdk
    • Android NDK location not configured (optional; useful for native profiling
      support)
    • Platform android-28, build-tools 28.0.3
    • Java binary at: /home/jake/Downloads/android-studio/jre/bin/java
    • Java version OpenJDK Runtime Environment (build
      1.8.0_152-release-1343-b16-5323222)
    • All Android licenses accepted.

[✓] Android Studio (version 3.4)
    • Android Studio at /home/jake/Downloads/android-studio
    • Flutter plugin version 37.0.1
    • Dart plugin version 183.6270
    • Java version OpenJDK Runtime Environment (build
      1.8.0_152-release-1343-b16-5323222)

[✓] Connected device (1 available)
    • ONEPLUS A6000 • 56390e16 • android-arm64 • Android 9 (API 28)

• No issues found!

错误：

快照: AsyncSnapshot(ConnectionState.waiting，null，错误:键入'_InternalLinkedHashMap‘不是’FutureOr‘的子类型)。

Answer 1

我修好了！我的getSpecialData()的返回类型是在未来中给出的，但是我的json文件是一个映射，所以我不得不将返回类型更改为未来。

Answer 2

你不能把东西还给我

 if (res.statusCode =! HttpStatus.OK)

在getSpecialData()中。

因为您是专门为这种情况编写代码的，所以您将获得null。