我的快照在futurebuilder中没有数据

分类：编程问答

如何解决我的快照在futurebuilder中没有数据

pls，请帮忙。我正尝试从rest api中获取一些数据。但是在getTreadingWallpapers（）方法上，它显示了完整的json数据。但是每当我在其他条件下打印snapshot.hasError时，它就会显示为false。这意味着快照没有错误..但是为什么我将来的构建器中没有得到数据。没有错误显示，我该如何解决这个问题

     class _FrontPageState extends State<FrontPage> {
 Future<List<RecentPage>> recentPage;
  RecentPage recentPagee;
  bool isLoading = true;
  List<RecentPage> wallpapers = new List();


  Future<List<RecentPage>> getTrendingWallpapers() async {
   // final url ="http://wallpaper.pkappstudio.info/api/api.php?action=get_recent";
    String url = 'http://wallpaper.pkappstudio.info/api/api.php?action=get_recent';
    final response =
    await Http.get(url,headers: {"Accept": "application/json"});
    if (response.statusCode == 200) {

      final Map = jsonDecode(response.body);
      print("${response.body}");
      isLoading = false;

      final recentPaget = recentPageFromJson(response.body).asMap();

      recentPaget.entries.forEach((element) => wallpapers.add(element.value));

      return wallpapers;
    } else {
      throw Exception('Failed to load post');
    }


  }

  @override
  void initState() {
    // TODO: implement initState
    recentPage = getTrendingWallpapers();
    super.initState();
  }
  @override
  Widget build(BuildContext context) {
    return Scaffold(
        backgroundColor: Colors.white,appBar: AppBar(title: brandName(),elevation: 0.0,),body: FutureBuilder(
          future: recentPage,builder: (context,snapshot) {
            if (snapshot.connectionState == ConnectionState.none &&
                snapshot.hasData == null) {
             print('project snapshot data is: ${snapshot.data}');
              return isLoading? Center(child: Container(child: Text("container"),)):Center(child: Container(child: Text("csdsdontainer"),));
            }
            if(snapshot.hasData){
              return isLoading? Center(child: CircularProgressIndicator()):ListView.builder(
                itemCount: snapshot.data.length,itemBuilder: (context,index){
                  return Container(
                    padding: EdgeInsets.symmetric(horizontal: 16),child: GridView.count(
                      shrinkWrap: true,crossAxisCount: 2,physics: ClampingScrollPhysics(),childAspectRatio: 0.6,mainAxisSpacing: 6.0,crossAxisSpacing: 6.0,children: wallpapers.map((wallpapers){
                        return GridTile(child: GestureDetector(
                          onTap: (){
                            //            Navigator.push(context,MaterialPageRoute(builder: (context)=>ImageView(
                            //              imageUrl: wallpapers.src.potrait,//            )));
                          },child: Container(
                            child:  ClipRRect(
                              borderRadius: BorderRadius.circular(10),child:Image.network(snapshot.data.imageUrl,fit: BoxFit.cover,));
                      }).toList(),);
                },);
            } else return Container(child: Text("${snapshot.hasError}"),);


          },)


    );
  }
}

解决方法

您可以在下面复制粘贴运行完整代码
步骤1：您不需要isLoading，可以直接使用支票ConnectionState
步骤2：您不需要声明List<RecentPage> wallpapers，snapshot.data已经保留此

代码段

builder: (context,AsyncSnapshot<List<RecentPage>> snapshot) {
      switch (snapshot.connectionState) {
        case ConnectionState.none:
          return Text('none');
        case ConnectionState.waiting:
          return Center(child: CircularProgressIndicator());
        case ConnectionState.active:
          return Text('');
        case ConnectionState.done:
          if (snapshot.hasError) {
            return Text(
              '${snapshot.error}',style: TextStyle(color: Colors.red),);
          } else {
            return ListView.builder(
              itemCount: snapshot.data.length,itemBuilder: (context,index) {
                return Container(
                  padding: EdgeInsets.symmetric(horizontal: 16),child: GridView.count(
                    shrinkWrap: true,crossAxisCount: 2,physics: ClampingScrollPhysics(),childAspectRatio: 0.6,mainAxisSpacing: 6.0,crossAxisSpacing: 6.0,children: snapshot.data.map((wallpapers) {
                      return GridTile(
                          child: GestureDetector(
                        onTap: () {
                          //            Navigator.push(context,MaterialPageRoute(builder: (context)=>ImageView(
                          //              imageUrl: wallpapers.src.potrait,//            )));
                        },child: Container(
                          child: ClipRRect(
                            borderRadius: BorderRadius.circular(10),child: Image.network(
                              wallpapers.imageUrl,fit: BoxFit.cover,

工作演示

enter image description here

完整代码

import 'package:flutter/material.dart';
import 'dart:convert';
import 'package:http/http.dart' as http;

List<RecentPage> recentPageFromJson(String str) =>
    List<RecentPage>.from(json.decode(str).map((x) => RecentPage.fromJson(x)));

String recentPageToJson(List<RecentPage> data) =>
    json.encode(List<dynamic>.from(data.map((x) => x.toJson())));

class RecentPage {
  RecentPage({
    this.no,this.imageId,this.imageUpload,this.imageUrl,this.type,this.viewCount,this.downloadCount,this.featured,this.tags,this.categoryId,this.categoryName,});

  int no;
  String imageId;
  String imageUpload;
  String imageUrl;
  Type type;
  String viewCount;
  String downloadCount;
  Featured featured;
  String tags;
  String categoryId;
  String categoryName;

  factory RecentPage.fromJson(Map<String,dynamic> json) => RecentPage(
        no: json["no"],imageId: json["image_id"],imageUpload: json["image_upload"],imageUrl: json["image_url"],type: typeValues.map[json["type"]],viewCount: json["view_count"],downloadCount: json["download_count"],featured: featuredValues.map[json["featured"]],tags: json["tags"],categoryId: json["category_id"],categoryName: json["category_name"],);

  Map<String,dynamic> toJson() => {
        "no": no,"image_id": imageId,"image_upload": imageUpload,"image_url": imageUrl,"type": typeValues.reverse[type],"view_count": viewCount,"download_count": downloadCount,"featured": featuredValues.reverse[featured],"tags": tags,"category_id": categoryId,"category_name": categoryName,};
}

enum Featured { YES,NO }

final featuredValues = EnumValues({"no": Featured.NO,"yes": Featured.YES});

enum Type { UPLOAD }

final typeValues = EnumValues({"upload": Type.UPLOAD});

class EnumValues<T> {
  Map<String,T> map;
  Map<T,String> reverseMap;

  EnumValues(this.map);

  Map<T,String> get reverse {
    if (reverseMap == null) {
      reverseMap = map.map((k,v) => new MapEntry(v,k));
    }
    return reverseMap;
  }
}

class FrontPage extends StatefulWidget {
  @override
  _FrontPageState createState() => _FrontPageState();
}

class _FrontPageState extends State<FrontPage> {
  Future<List<RecentPage>> recentPage;
  RecentPage recentPagee;
  bool isLoading = true;
  List<RecentPage> wallpapers = new List();

  Future<List<RecentPage>> getTrendingWallpapers() async {
    // final url ="http://wallpaper.pkappstudio.info/api/api.php?action=get_recent";
    String url =
        'http://wallpaper.pkappstudio.info/api/api.php?action=get_recent';
    final response =
        await http.get(url,headers: {"Accept": "application/json"});
    if (response.statusCode == 200) {
      final Map = jsonDecode(response.body);
      print("${response.body}");
      isLoading = false;

      final recentPaget = recentPageFromJson(response.body).asMap();

      recentPaget.entries.forEach((element) => wallpapers.add(element.value));

      return wallpapers;
    } else {
      throw Exception('Failed to load post');
    }
  }

  @override
  void initState() {
    // TODO: implement initState
    recentPage = getTrendingWallpapers();
    super.initState();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
        backgroundColor: Colors.white,appBar: AppBar(
          title: Text("brandName()"),elevation: 0.0,),body: FutureBuilder(
            future: recentPage,builder: (context,AsyncSnapshot<List<RecentPage>> snapshot) {
              switch (snapshot.connectionState) {
                case ConnectionState.none:
                  return Text('none');
                case ConnectionState.waiting:
                  return Center(child: CircularProgressIndicator());
                case ConnectionState.active:
                  return Text('');
                case ConnectionState.done:
                  if (snapshot.hasError) {
                    return Text(
                      '${snapshot.error}',);
                  } else {
                    return ListView.builder(
                      itemCount: snapshot.data.length,index) {
                        return Container(
                          padding: EdgeInsets.symmetric(horizontal: 16),child: GridView.count(
                            shrinkWrap: true,children: snapshot.data.map((wallpapers) {
                              return GridTile(
                                  child: GestureDetector(
                                onTap: () {
                                  //            Navigator.push(context,MaterialPageRoute(builder: (context)=>ImageView(
                                  //              imageUrl: wallpapers.src.potrait,//            )));
                                },child: Container(
                                  child: ClipRRect(
                                    borderRadius: BorderRadius.circular(10),child: Image.network(
                                      wallpapers.imageUrl,));
                            }).toList(),);
                      },);
                  }
              }
            }));
  }
}

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',theme: ThemeData(
        primarySwatch: Colors.blue,visualDensity: VisualDensity.adaptivePlatformDensity,home: FrontPage(),);
  }
}

class MyHomePage extends StatefulWidget {
  MyHomePage({Key key,this.title}) : super(key: key);

  final String title;

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

class _MyHomePageState extends State<MyHomePage> {
  int _counter = 0;

  void _incrementCounter() {
    setState(() {
      _counter++;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text(widget.title),body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.center,children: <Widget>[
            Text(
              'You have pushed the button this many times:',Text(
              '$_counter',style: Theme.of(context).textTheme.headline4,],floatingActionButton: FloatingActionButton(
        onPressed: _incrementCounter,tooltip: 'Increment',child: Icon(Icons.add),// This trailing comma makes auto-formatting nicer for build methods.
    );
  }
}
,

FutureBuilder小部件的实现很好

Future<List<dynamic>> getTrendingWallpapers() async {
  String url = 'http://wallpaper.pkappstudio.info/api/api.php?action=get_recent';
  final response = await http.get(url,headers: {"Accept": "application/json"});
  if (response.statusCode == 200) {
    List<dynamic> wallpapers = List();
    wallpapers.add(response.body);

    return wallpapers;
  } else {
    throw Exception('Failed to load post');
  }
}

@override
Widget build(BuildContext context) {
  return Scaffold(
    body: FutureBuilder(
      future: getTrendingWallpapers(),snapshot) {
        if (snapshot.connectionState == ConnectionState.waiting || snapshot.connectionState == ConnectionState.none) {
          return Center(child: CircularProgressIndicator());
        }

        if (snapshot.hasError) {
          return Center(
            child: Text('Future error'),);
        }
        if (snapshot.hasData) {
          return Center(
            child: Text('Do something with your snapshot.data : \n ${snapshot.data}'),);
        }
      },);
}

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