Flutter generic REST API call function - flutter

Question

I am working on first my flutter app. App required to call rest api and return back result. I am looking to create generic function to call rest api. I have written below code but I am not understating, how can I decode api response in specific model.
Future<T> apiRequest<T>(
String endPoint,
RequestMethod method, {
String body = '',
String token = '',
}) async {
http.Response resp;
final String url = LocalConstants.apiBaseUrl + endPoint;
final Map<String, String> headers = new Map<String, String>();
headers.putIfAbsent(
HttpHeaders.contentTypeHeader, () => 'application/json');
if (token != null && token.isNotEmpty) {
headers.putIfAbsent(
HttpHeaders.authorizationHeader, () => 'Bearer ' + token);
}
try {
if (method == RequestMethod.get) {
resp = await http.get(
url,
headers: headers,
);
} else if (method == RequestMethod.put) {
resp = await http.put(
url,
headers: headers,
body: body,
);
} else if (method == RequestMethod.post) {
resp = await http.post(
url,
headers: headers,
body: body,
);
} else if (method == RequestMethod.delete) {
resp = await http.delete(
url,
headers: headers,
);
}
if (resp != null && this.validateResponse(resp)) {
return json.decode(resp.body);
}
// else {
// Response resp = new Response();
// resp.respMsg = LocalConstants.genericError;
// resp.respCode = LocalConstants.resp_failure;
// Response.
// }
} on TimeoutException catch (e) {
//handleTimeout();
} on SocketException catch (e) {
print('Socket Error: $e');
//handleTimeout();
} on Error catch (e) {
print('General Error: $e');
//showError();
}
}
Below is code which I can use to call rest api
await ApiService.newInstance(context)
.apiRequest<GenericResp>('/api/people', RequestMethod.get);
Here is my GenericResp class
import 'package:project/models/Response.dart';
class GenericResp extends Response {
int id;
int otherId;
String mappingId;
GenericResp({
this.id,
this.otherId,
this.mappingId,
});
GenericResp.fromJson(Map<String, dynamic> json) {
id = json['id'];
otherId = json['other_id'];
mappingId = json['mapping_id'];
respCode = json['resp_code'];
respMsg = json['resp_msg'];
}
Map<String, dynamic> toJson() {
final Map<String, dynamic> data = <String, dynamic>{};
data['id'] = this.id;
data['other_id'] = this.otherId;
data['mapping_id'] = this.mappingId;
data['resp_code'] = this.respCode;
data['resp_msg'] = this.respMsg;
return data;
}
}
How can I decode body json.decode(resp.body); to GenericResp of type T?

Answer 1

You can add a generic argument that will deserialize your json data to GenericResp. Something like that:
Future<T> apiRequest<T>(
String endPoint,
RequestMethod method, T Function(Object json) fromJson, {
String body = '',
String token = '',
}) async { ... }
And after json decoding you are to use fromJson argument:
if (resp != null && this.validateResponse(resp)) {
return fromJson(json.decode(resp.body));
}
And then a call would look like this:
await ApiService.newInstance(context).apiRequest<GenericResp>('/api/people',
RequestMethod.get, (json) => GenericResp.fromJson(json));