How to create a specific type of nested JSON data in Dart?

Question

I have a model like:

class PotholeData {
    List<Coordinates> coordinates; 
    String location; 
    String image;

    PotholeData({this.coordinates, this.location, this.image});

    PotholeData.fromJson(Map<String, dynamic> json) {
        if (json['coordinates'] != null) {       
            coordinates = new List<Coordinates>();       
            json['coordinates'].forEach((v) {         
            coordinates.add(new Coordinates.fromJson(v));       
            });     
        }     
        location = json['location'];     
        image = json['image'];   
    }

    Map<String, dynamic> toJson() 
    { 
    final Map<String, dynamic> data = new Map<String, dynamic>();
    if (this.coordinates != null) {       
        data['coordinates'] = this.coordinates.map((v) => v.toJson()).toList();     }
        data['location'] = this.location;
        data['image'] = this.image; 
        return data;   
        } 
    }

class Coordinates { 
    String x; 
    String y; 
    String w; 
    String h;

    Coordinates({this.x, this.y, this.w, this.h});

    Coordinates.fromJson(Map<String, dynamic> json) { 
        x = json['x']; 
        y = json['y']; 
        w = json['w']; 
        h = json['h']; 
    }

    Map<String, dynamic> toJson() { 
        final Map<String, dynamic> data = new Map<String, dynamic>(); 
        data['x'] = this.x; 
        data['y'] = this.y;
        data['w'] = this.w;
        data['h'] = this.h; 
        return data;
    } 
}

I am trying to put this data into Firebase and the way I am doing is:

Map<String, dynamic> potholeData = PotholeData(
    coordinates: sampleCoordinates,
    image: "File name",
    location: "Live Location").toJson();

obj.addData(potholeData).catchError((e) { 
    print(e);
    });     
}

where the sampleCoordinates is a list of type coordinates. But I am not getting what form of data should be in it. I was trying out with hardcoded data in it but every time I put anything an error pops up stating the element of type List/Map/String/int can't be assigned to the list type Coordinates.

The sample JSON data looks like:

{
    "coordinates": [
        {
            "x": "x_coor",
            "y": "y_coor",
            "w": "width",
            "h": "heigth"
        },
        {
            "x": "x_coor",
            "y": "y_coor",
            "w": "width",
            "h": "heigth"
        }
    ],
    "location": "location",
    "image": "image"
}

I need help in understanding what kind of data should be inside sampleCoordinates. Should it be a Map/List/String/int? sampleCoordinates is hardcoded for your information.

I had tried putting some data like below but none of them worked. Technically, the first one should have worked. The following was tried:

List<Coordinates> sampleCoordinates = [{
            "x": "x_coor",
            "y": "y_coor",
            "w": "width",
            "h": "heigth"
        },
        {
            "x": "x_coor",
            "y": "y_coor",
            "w": "width",
            "h": "heigth"
        }];

OR
List<Coordinates> sampleCoordinates = [123,1234];

OR
List<Coordinates> sampleCoordinates = ["asb","adgad"];

Does this answer your question? Create Json Arrays and List with SharedPreferences — Kahou
– Kahou, Commented Mar 1, 2020 at 14:57
@Kahou No, it doesn't. That question is purely for SharedPrefs and it doesn't show how to create nested JSON data of a specific type! — JOSEPH Blessingh
– JOSEPH Blessingh, Commented Mar 1, 2020 at 15:03

Kahou · Accepted Answer · 2020-03-01 15:26:07Z

1

The user class with JSON convert: JSON and serialization

class User {
  String name;
  int age;
  User father;

  User({
    this.name,
    this.age,
    this.father,
  });

  factory User.fromJson(String str) => User.fromMap(json.decode(str));

  String toJson() => json.encode(toMap());

  factory User.fromMap(Map<String, dynamic> json) => User(
        name: json["name"],
        age: json["age"],
        father: json["father"] == null ? null : User.fromMap(json["father"]),
      );

  Map<String, dynamic> toMap() => {
        "name": name,
        "age": age,
        "father": father == null ? null : father.toMap(),
      };
}

answered Mar 1, 2020 at 15:26

Kahou

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1 Comment

JOSEPH Blessingh Over a year ago

I don't want to serialize my data. I edited my question after your comment. I want to create JSON data which has a List of a specific type i.e. Coordinates in this case. Check my answer which I have posted. You will understand what I wanted!! Cheers for trying to help me out

JOSEPH Blessingh · Accepted Answer · 2020-03-01 16:10:51Z

0

So, I found the answer while trying out many things. The sampleCoordinates should have:

List<Coordinates> sampleCoordinates = [
    Coordinates(h: '24',w: '3455', x: '34', y: '345'), 
    Coordinates(h: '24',w: '3455', x: '34', y: '345')
];

This served my purpose.

answered Mar 1, 2020 at 16:10

JOSEPH Blessingh

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