Could not set header with dio - flutter

Question

I ma not able to set header with dio.I am tryng to set my access token to the header.I ma trying to set header so that every request doesnt required to call it.Here is my network class where i am trying to call header with dio
My network Class:
class NetworkUtil {
Dio _dio;
String token;
getToken() async {
SharedPreferences preferences = await SharedPreferences.getInstance();
String getToken = preferences.getString(AppPrefernces.LOGIN_PREF);
return getToken;
}
NetworkUtil() {
///Create Dio Object using baseOptions set receiveTimeout,connectTimeout
BaseOptions options = BaseOptions(receiveTimeout: 5000, connectTimeout: 5000);
options.baseUrl = ApiConstants.BASE_URL;
_dio = Dio(options);
_dio.interceptors.add(InterceptorsWrapper(
onRequest: (Options option) async{
//my function to recovery token
await getToken().then((result) {
LoginResponse loginResponse = LoginResponse.fromJson(jsonDecode(result));
token = loginResponse.accessToken;
});
option.headers = {
"Authorization": "Bearer $token"
};
}
));
}
///used for calling Get Request
Future<Response> get(String url, Map<String, String> params) async {
Response response = await _dio.get(url,
queryParameters: params,
options: Options(responseType: ResponseType.json));
return response;
}
///used for calling post Request
Future<Response> post(String url, Map<String, String> params) async {
Response response = await _dio.post(url,
data: params, options: Options(responseType: ResponseType.json));
return response;
}
}

Answer 1

I use this setup and it works fine for me.
Future<Dio> createDioWithHeader() async {
if (_dioWithHeader != null) return _dioWithHeader;
String token = await appSharedPreferences.getToken();
String userAgent = await getUserAgent();
print('User-Agent: $userAgent');
// base config
_dioWithHeader = Dio(BaseOptions(
connectTimeout: 10000,
receiveTimeout: 10000,
baseUrl: Config.apiBaseUrl,
contentType: 'application/json',
headers: {
'Authorization': token,
'User-Agent': userAgent
}));
// setup interceptors
return addInterceptors(_dioWithHeader);
}```