Why Flutter http POST request not response - flutter

Question

I want to make login system in flutter with the following code:
api/api.dart
import 'dart:convert';
import 'package:http/http.dart' as http;
import 'package:shared_preferences/shared_preferences.dart';
class CallApi {
final String _url = 'http://10.0.2.2:8000/api/';
postData(data, apiUrl) async {
var fullUrl = _url + apiUrl + await _getToken();
return await http.post(fullUrl,
body: jsonEncode(data), headers: _setHeaders());
}
getData(apiUrl) async {
var fullUrl = _url + apiUrl + await _getToken();
return await http.get(fullUrl, headers: _setHeaders());
}
_setHeaders() => {
'Content-type': 'application/json',
'Accept': 'application/json',
};
_getToken() async {
SharedPreferences localStorage = await SharedPreferences.getInstance();
var token = localStorage.getString('token');
return '?token=$token';
}
}
login_screen.dart
void _login() async {
var data = {
'email': mailController.text,
'password': passwordController.text
};
var res = await CallApi().postData(data, 'login');
var body = json.decode(res.body);
if (body['success']) {
SharedPreferences localStorage = await SharedPreferences.getInstance();
localStorage.setString('token', body['token']);
localStorage.setString('user', json.encode(body['user']));
Navigator.push(
context, new MaterialPageRoute(builder: (context) => HomePage()));
} else {
_showMsg(body['message']);
}
}
The problem is this doesn't work. and after trying to find the location of the error, I found that the following code did not return anything
postData(data, apiUrl) async {
........
return await http.post(fullUrl,
body: jsonEncode(data), headers: _setHeaders());
}
I don't know the exact cause, please help me