Handle null values in JSON parsing in a Flutter app

Question

I am fetching the details from database and then I am parsing the json value. Below is the code for http request.

Future <List> getData() async{
    
   if(endofrecord == false){
    try{  
      
      var body = { "uid" : dtguid, "deviceid": deviceid, "offset": offset};
      var url = 'http://192.168.1.100:8080/get_recommended.php';

                    // Starting Web API Call.
           var response = await http.post(url, body: json.encode(body)).timeout(Duration(seconds: 5),
            onTimeout: (){
                    //  throw Exception();
              _showSnackBar(context,'Some issue with connectivity. Can not reached to server.',Colors.redAccent);
                      //or you can also
              return null;
            });
         if(response.statusCode == 200){
           final data = parsedataFromJson(response.body);
                      setState(() {
                        recommended = true; 
                        _inProcess = false;
                        if(data.count == null){
                          count = 0;
                        }else{
                          offset = offset + 5;
                          print(offset);
                          count = data.count;
                        }
                      if(data.content.length > 0 && data.content[0].name != 'Empty'){
                        for (var i in data.content) {
                          lists.add(i);
                        }  
                      }else{
                        nodata = 'No Record Found';
                        endofrecord = true;
                        _showSnackBar(context,nodata,Colors.redAccent);
                      }
                    
                      });
                print(lists.length);
                
         }
     
    }catch(e){
       print("Exception Caught: $e");
       _showSnackBar(context,'Some issue with connectivity. Could not connect to server.',Colors.redAccent);
    }
 return lists;
    }else{
      return null;
    }
  }

Here is the JSON parsing.

import 'dart:convert';

DatabyPrice databyPriceFromJson(String str) => DatabyPrice.fromJson(json.decode(str));

class DatabyPrice {
    DatabyPrice({
        this.count,
        this.content,
        this.success,
    });

    int count;
    List<Content> content;
    bool success;

    factory DatabyPrice.fromJson(Map<String, dynamic> json) => DatabyPrice(
        count: json["count"],
        content: List<Content>.from(json["content"].map((x) => Content.fromJson(x))),
        success: json["success"],
    );
}

class Content {
    Content({
        this.name,
        this.uid,
        this.pic,
        this.state,
        this.country,
        this.lastLogin,
        this.tabout,
        this.averageOrating,
        this.pricing,
    });

    String name;
    int uid;
    String pic;
    String state;
    String country;
    String tabout;
    String lastLogin;
    String averageOrating;
    List<Pricing> pricing;

    factory Content.fromJson(Map<String, dynamic> json) => Content(
        name: json == null ? 'Empty' : json["name"],
        uid: json == null ? 0 :json["uid"],
        pic: json == null ? 'Empty' :json["pic"],
        state: json == null ? 'Empty' :json["state"],
        tabout: json == null ? 'Empty' :json["tabout"],
        country: json == null ? 'Empty' :json["country"],
        lastLogin: json == null ? 'Empty' : json["last_login"],
        averageOrating: json == null ? '0' :json["average_orating"],
        pricing: List<Pricing>.from(json["pricing"].map((x) => Pricing.fromJson(x))),
    );

}

class Pricing {
    Pricing({
        this.uid,
        this.price,
        this.serviceType,
    });

    int uid;
    int price;
    String serviceType;

    factory Pricing.fromJson(Map<String, dynamic> json) => Pricing(
        uid: json == null ? 0 :json["uid"],
        price: json == null ? 0 :json["price"],
        serviceType: json == null ? 'Empty' :json["service_type"],
    );

}

Above code is working fine when there are some records returning from database but if there is no data or end of record then it is not working. I am getting below error.

I/flutter ( 5255): Receiver: null
I/flutter ( 5255): Tried calling: []("pricing")
I/flutter ( 5255): Exception Caught: NoSuchMethodError: The method '[]' was called on null.

How can I handle this situation when http request is not returning the data?

Answer 1

For converting the JSON into a PODO, you must use something like JSON to Dart

Once the model is generated then it would be easy for you to check the null elements coming from the backend.

Answer 2

Did you catch any error in the try{} catch{} block.If your experiencing no errors check your custom JSON converter.Try testing without your custom JSON parsers and use the normal converter which converts JSON into a Map.If it still not working make sure you've import the dart:async module like this import dart:asyncdart.If it doesn't change anything try using the .then() and .catch() syntax .If not try checking your backend database they may be something wrong