json - Pure Dart output error working with Model and Lists - Stack Overflow

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hi I am trying to retrieve nestedJson to dart, mainly Ill be working with API call which has similar data nested Json so this below is example I was trying if it works. so my main problem is I am not getting Expected output. below mentioned are my code files, if this seems wrong or tedius way, kindly guide me the right way to do it.

EXPECTED OUTPUT:	OUTPUT I GET:
dastagir	dastagir
34	34
Shangai	Shangai
[]	[]
============	============
china
Bangladesh

hi I am trying to retrieve nestedJson to dart, mainly Ill be working with API call which has similar data nested Json so this below is example I was trying if it works. so my main problem is I am not getting Expected output. below mentioned are my code files, if this seems wrong or tedius way, kindly guide me the right way to do it.

EXPECTED OUTPUT:	OUTPUT I GET:
dastagir	dastagir
34	34
Shangai	Shangai
[]	[]
============	============
china
Bangladesh

main.dart
void main() {

var myMap = {
"name": "dastagir",
"age": 34,
"city":"Shangai",
 
 "address": [
   { // Map 1
    "country": "china",
    "city": "Shanghai"
   },
   { // Map 2
     "country": "Bangaldesh",
     "city": "Dhaka"
   },
 ]
};
var obj = Person.fromJson(myMap);
print(obj.name);
print(obj.age);
print(obj.city);
print(obj.address);
print("=======================================");

var myAddress = obj.address;
myAddress!.map((e){
print(e.country);
 }).toList();
}

nested_json.dart
class Person{
  String? name;
  int? age;
  String? city;
  List<Address>? address;
  Person({this.name, this.age, this.city, this.address});

  Person.fromJson(Map<String, dynamic> json){
    name = json['name'];
    age = json['age'];
    city = json['city'];

    if(json['address']!=null){
      address=<Address>[];
    }
    else{
        (json['address'] as List).forEach((e){
          address!.add(Address.fromJson(e));
        });
    }
  }
}

// this is for inner Json List
class Address{
  String? country;
  String? city;
    
  Address({this.country, this.city});

  Address.fromJson(Map<String, dynamic> json){
    country = json['country'];
    city = json['city'];
  }
}`

• json
• dart
• visual-studio-code
• parsing
• debugging

Share Improve this question Follow asked Mar 6 at 17:30 appdevappdev 1599 bronze badges 3

• I think your error is here: json['address']!=null. If you have items, you're setting address to empty list, but then never adding the individual addresses. If you have no items, that code is likely to blow up. – Randal Schwartz Commented Mar 6 at 19:10
• 1 got it, I was making list but wasn't filling data instead just making empty list then and else condition would never work how do I mark you as HELPED PERFECTLY? I don't see an option to mark this answer as solved – appdev Commented Mar 6 at 22:40
• Don't worry about me. Just glad you found your solution. – Randal Schwartz Commented Mar 6 at 23:13

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2 Answers 2

Sorted by: Reset to default 3

You're using print function in map, but print returns void. map is used for mapping one type into another, not for void action.

myAddress!.map((e){
print(e.country);
 }).toList();
}

It's better to use forEach

myAddress?.forEach((e) => print(e));

or for loop

for (final address in (myAddress ?? const []) {
    print(address);
}

[Extracting the answer from the comments for better visibility...]

I think your error is here: json['address']!=null. If you have items, you're setting address to empty list, but then never adding the individual addresses. If you have no items, that code is likely to blow up.

The solution is to fix the boolean conditions so they do the right thing. Initialize with an empty list, and for each item present, add that to the list.

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