Generic deserialization in Flutter / Dart - flutter

Question

I'm trying to write a HTTP driver class that takes in a generic class and deserializes the response. I haven't found a good, clean way to do this in Flutter.
I've defined datamodel classes like this:
class MyClass {
String field1;
String field2;
MyClass.fromJson(Map<dynamic, dynamic> json)
: field1 = json["field1"],
field2 = json["field2"];
}
This works well and good if I do it manually...
MyClass makeRequest() {
Response response = http.get(url);
MyClass class = MyClass.fromJson(jsonDecode(response.body));
return class;
}
What I want, is to make a generic HTTP driver like this:
void makeRequest<T>() {
Response response = http.get(url);
T parsed = T.fromJson(jsonDecode(response.body));
return parsed;
}
Is there a way to do this in Flutter/Dart? I've been trying to figure out the right syntax to use a base class and extends but haven't gotten it. Any ideas?

Answer 1

This is what I usually use in my network call, feel free to use. Btw, I recommend the dio package for convenient headers and params config, as well as other error handling features.
// Define an extension
extension BaseModel on Type {
fromJson(Map<String, dynamic> data) {}
}
// For single object
Future<T> makeGetRequest<T>({String url, Map<String, dynamic> params}) {
return http
.get(buildUrl(url, params)) // Don't need the buildUrl() if you use Dio
.then((response) => handleJsonResponse(response))
.then((data) => T.fromJson(data));
// For list of object
Future<List<T>> makeGetRequestForList<T>({String url, Map<String, dynamic> params}) {
return http
.get(buildUrl(url, params)) // Don't need the buildUrl() if you use Dio
.then((response) => handleJsonResponse(response))
.then((data) => List<T>.from(data.map((item) => T.fromJson(item)));
}
// Helper classes without Dio
String buildUrl(String url, [Map parameters]) {
final stringBuilder = StringBuffer(url);
if (parameters?.isNotEmpty == true) {
stringBuilder.write('?');
parameters.forEach((key, value) => stringBuilder.write('$key=$value&'));
}
final result = stringBuilder.toString();
print(result);
return result;
}
// With Dio, you can simply do this:
final res = await API().dio
.get(url, queryParameters: params) // Don't need the [buildUrl] here
.then((response) => handleJsonResponse(response))
.then((data) => T.fromJson(data));
// Handle JSON response
handleJsonResponse(http.Response response, [String endpoint = '']) {
print(
'API: $endpoint \nCODE: ${response.statusCode} \nBODY: ${response.body}');
if (_okStatus.contains(response.statusCode)) {
return jsonDecode(response.body);
}
if (response.statusCode == HttpStatus.unauthorized) {
throw Exception(response.statusCode);
} else {
throw Exception("HTTP: ${response.statusCode} ${response.body}");
}
}
Usage:
// Example class
class Post {
final String title;
Post({this.title});
#override
Post.fromJson(Map<String, dynamic> data) : title = data['title'];
}
// Use the function
Future<Post> getPost() async {
final result = await makeGetRequest<Post>(params: {'post_id': 1});
return result;
}