CODEWITHSUNDEEP
jsonlistflutterobjectmaps
nejas
nejas

Reputation: 19

In flutter - how do I best handle and assign predetermined keys to nested lists/arrays in json

I'm sending data over ble and have compacted the json strings. The json contains three arrays.

{"b":false,"l":261,"a":["0.5","1.8","2.9","1.0"]}

I have a model class of Notify. I need to create a model class for "a" that assigns a predefined key to each of the values in the list but I am not sure of the best way. The values always come in a specific order.

class Notify{
  bool b;
  int l;
  List<String> a;

  Notify({this.b, this.a, this.d, this.p});

  Notify.fromJson(Map<String, dynamic> json) {
  b = json['b'];
  l = json['l'];
  a = json['a'].cast<String>();
  }

  Map<String, dynamic> toJson() {
    final Map<String, dynamic> data = new Map<String, dynamic>();
    data['b'] = this.b;
    data['l'] = this.l;
    data['a'] = this.a;
    return data;
  }
}

I get lost in the steps. In this class I think I need to:

  1. Turn the "a" array into a list.
  2. Convert the Strings to doubles.
  3. Convert to a Map providing a key of a0, a1, a2, a3 to the four items in the "a" list.
  4. Add four more items to the overall class/map based on a0-a3. Example: a4 = a0 * -1, a5 = a1 * -1, a6 = a2 * -1, a7 = a3.
  5. Make it available and usable to the Notify class.
    class A {
      double a0;
      double a1;
      double a2;
      double a3;
      double a4;
      double a5;
      double a6;
      double a7;
    
      A a;
    
      A({this.a0, this.a1, this.a2, this.a3, this.a4, this.a5, this.a6, this.a7});
    
      A.fromJson(List<double> json){
// Do bring it in as a list?
        List<double> angleValuesList = List<double>.from(json);
        List<String> angleKeysList = ['a0', 'a1', 'a2', 'a3'];
        Map<String, double> angleMap = Map.fromIterables(angleKeysList, angleValuesList);
// Then I map the first four values to a0-a3
        //now lost..... how do I get close to items 3-5?
        }
      }

I'm hoping my map looks like this so I can create an object from it and drop it in a stream. I receive this packet every 16 milliseconds:

{"b":false,"l":261,"a":["a0": "0.5", "a1":"1.8", "a2":"2.9", "a3":"1.0", "a4": "-0.5", "a5":"-1.8", "a6":"-2.9", "a7":"-1.0"]}

Thanks for taking the time to read through this!

Upvotes: 0

Views: 105

Answers (1)

Yadu
Yadu

Reputation: 3305

if you parse this {"b":false,"l":261,"a":["0.5","1.8","2.9","1.0"]} using json.decode(data) like this you will end up having this

data = {"b":false,"l":261,"a":["0.5","1.8","2.9","1.0"]}

steps

Map<String,dynamic> map = json.decode(data);
//as you know the data you have provided
bool b = map['b'] as bool;
int l = map['l'] as int;
//as the list is of type string ["2.2","3.1"]
List<String> a = List.castFrom(map['a']);//or map['a'] as Map<String>
//if the list could have been of type double [2.2,3.1,4.2]
List<double> a = List.castFrom(map['a']);//or map['a'] as Map<double>

Upvotes: 1

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