I just want to fetch the whole list of my model and in my response>

I cannot assign the result of the HTTP request to the list. Could anybody provide me what I'm missing in my code?

I want to fetch the whole list of 20 items as count param says but I'm getting a single response.body and it is not possible to assign it to a list which I expect. How to convert it to a list?

My error: Cannot assinge Future to Future<List>

Base response:

class ApiService {
  String baseUrl = astronomyApiUrl;

  Future<http.Response> fetchData(Map<String, String> urlParams) async {
    http.Response response;
    var combinedUrl = combineUrl(urlParams: urlParams);

    final url = Uri.parse(combinedUrl);
    try {
      response = await http.get(url);
    } on Exception catch (e) {
      throw e;
    }
    return response;
  }

  String combineUrl({Map<String, String>? urlParams}) {
    final buffer = StringBuffer();
    urlParams!.forEach((name, value) {
      buffer.write("$name=$value&");
    });

    return "$baseUrl/api/?${buffer.toString()}";
  }
}

List response:

class AstronomyService {
  Future<List<AstronomyModel>?> getAstronomy() async {
    try {
      final response = await ApiService().fetchData({
        "thumbs": true.toString(),
        "count": "20",
      });

      if (response.statusCode == 200) {
        final result = astronomyModelFromJson(response.body);
        return result; //Cannot assinge Future<AstronomyModel> to Future<List<AstronomyModel>>
      } else {
        return null;
      }
    } on SocketException catch (e) {
      throw e;
    } on HttpException catch (e) {
      throw e;
    } on FormatException catch (e) {
      throw e;
    }
  }
}

Model:

AstronomyModel astronomyModelFromJson(String str) =>
    AstronomyModel.fromJson(json.decode(str));

class AstronomyModel {
  AstronomyPicModel({
    this.date,
    this.hdurl,
    this.description,
    this.mediaType,
    this.thumbnailUrl,
    this.title,
    this.url,
  });

  DateTime? date;
  String? hdurl;
  String? description;
  String? mediaType;
  String? thumbnailUrl;
  String? title;
  String? url;

  factory AstronomyModel.fromJson(Map<String, dynamic> json) =>
      AstronomyModel(
        date: DateTime.parse(json["date"]),
        hdurl: json["hdurl"],
        description: json["description"],
        mediaType: json["media_type"],
        thumbnailUrl: json["thumbnail_url"],
        title: json["title"],
        url: json["url"],
      );
}

CodePudding user response：

Your AstronomyModel.fromJson just creates a single AstronomyModel.

So your astronomyModelFromJson(response.body) will just create a single one too.

As you provide no indication as to what the API is, or what the response.body is, this is just a guess:

Assuming that API call does return a list (why don't you look at it, and print it out? print(response.body);), then perhaps what you want to do is something like:

final result = response.body.map((a)=> astronomyModelFromJson(a));

CodePudding user response：

I messed up in model part. I was decoding just single response instead of list.

Solution was just to replace this:

AstronomyModel astronomyModelFromJson(String str) =>
    AstronomyModel.fromJson(json.decode(str));

To this:

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

CodePudding user response：

Actually you are having this issue because astronomyModelFromJson method will return you AstronomyModel while the Future is waiting to return List. You should try doing something like this

   class AstronomyService {
 Future<List<AstronomyModel>?> getAstronomy() async {
   try {
     final response = await ApiService().fetchData({
       "thumbs": true.toString(),
       "count": "20",
     });

     if (response.statusCode == 200) {
       final items = json.decode(response.body).cast<Map<String, dynamic>>();
       List<AstronomyModel> result = items.map<AstronomyModel>((json) {
       return AstronomyModel.fromJson(json);
     }).toList();
     return result;
     } else {
       return null;
     }
   } on SocketException catch (e) {
     throw e;
   } on HttpException catch (e) {
     throw e;
   } on FormatException catch (e) {
     throw e;
   }
 }
}

CodePudding user response：

 try {
      final response = await ApiService().fetchData({
        ListView.builder(
                    itemCount:20           
      });

.try list view builder instead may be it works and try to initialize

List<AstronomyModel>

.on your screen may be it works. thanks