Common generic class to handle server response in flutter - http

Question

I'm calling requesting server for data and getting following response.
{
"success": 1,
"data": [
{
"id": 1,
"name": "Kurti"
},
{
"id": 2,
"name": "Top"
}
],
"message": "Data fetched"
}
Modal class to convert json data coming from server.
class Product {
String categoryName;
int productId;
Product.fromJson(Map<String, dynamic> json) {
categoryName = json["id"];
productId = json["name"];
}
}
So from the server the format will be fix for every call like below...
{
"success": <Int>,
"message": <String>,
"data": <An array of Model class>
}
For that I've created below class...
class ServerResponse<T> {
String message;
int success;
List<T> data;
ServerResponse.fromJson(Map<String, dynamic> json) {
message = json["message"];
success = json["success"];
data = json["product_data"];
}
}
And this is how I'm calling api...
class ServerManager {
final baseUrl = isProduction ? liveServer : stagingServer;
var headers = {"consumer-key": "sdfgdqwrtw34563t545"};
dynamic callWSToGetData({Map<String, String> params}) async {
var client = http.Client();
var url = baseUrl + allProducts;
print("URL = $url");
print("params: $params");
print("header: $headers");
var response = await client.post(url, headers: headers, body: params);
var json = converter.jsonDecode(response.body);
return json;
}
}
Calling api to get data as following.
Map<String, String> params = {"categories_id": "1", "language_id": "1", "type": "Newest", "customers_id": "0", "page_number": "0"};
var response = ServerManager().callWSToGetData(params: params);
var res = ServerResponse<Product>.fromJson(response);
print(res.data);
So when I ran this code I'm getting following error.
type 'Future' is not a subtype of type 'Map'
The question is...
How can I create a single generic class that can be used to handle server responses?
Any help please.

Answer 1

type 'Future' is not a subtype of type 'Map'
This is probably due to missing await call. Your callWSToGetData has async in declaration so it's type will be Future.
To use generics you need to pass the type. So your code will look like this:
var response = await ServerManager().callWSToGetData(); //how can I use generic here
var res = ServerResponse<Product>.fromJson(response);
print(res.data);