Parsing complex JSON in Flutter

Gives a detailed explanation of working with simple and complex JSON structures using dart:convert library in Flutter along with a sample project with 6+ examples to experiment with.

Tutorial

Read the Medium article here

Types of JSON structures

Simple map
Simple structure with arrays
Simple nested structures
Nested structure with Lists
List of maps
Complex nested structures
Simple structure with Nested Maps [parsed using json_serializable library]
Demo for Network Calls with examples for GET, POST methods along with FutureBuilder and .then()

How to work with Network Calls?

Not covered in the article

Let's take this API as an example.

Take a look at post_model.dart for the model class and utility methods. I produced it using this converter tool

GET getAllPosts

//services.dart
Future<List<Post>> getAllPosts() async {
  final response = await http.get(url);
  return allPostsFromJson(response.body);
}

// As a part of your UI widget, e.g body of Scaffold widget
FutureBuilder<List<Post>>(
            future: getAllPosts(),
            builder: (context, snapshot) {
              if(snapshot.hasData)
                return Text('Title from Post JSON : ${snapshot.data[0].title}');
              else
                return CircularProgressIndicator();
            }
        )

GET getPost (to get a particular POST by id)

//services.dart
Future<Post> getPost() async{
  final response = await http.get('$url/1'); // the number is the id of the item being accessed
  return postFromJson(response.body);
}

// As a part of your UI widget, e.g body of Scaffold widget
FutureBuilder<Post>(
            future: getPost(),
            builder: (context, snapshot) {
              if(snapshot.hasData)
                return Text('Title from Post JSON : ${snapshot.data.title}');
              else
                return CircularProgressIndicator();
            }
        )

POST createPost

//services.dart
Future<http.Response> createPost(Post post) async{
  final response = await http.post('$url',
      headers: {
        HttpHeaders.contentTypeHeader: 'application/json'
      },
      body: postToJson(post)
  );

  return response;
}

  //call this function when you want to create a new post
 callAPI(){
    Post post = Post(
      body: 'Testing body body body',
      title: 'Flutter jam6'
    ); // creating a new Post object to send it to API
    
    createPost(post).then((response){
        if(response.statusCode > 200)
          print(response.body);
        else
          print(response.statusCode);
    }).catchError((error){
      print('error : $error');
    });
    
  }