init method
first you must call the init() method
the token will be searched in local storage
the appID
parameter is the identifier of your application. You can find it here https://vk.com/apps?act=manage
appId
by default - VK Me app ID
Implementation
Future<void> init({appId = 6146827}) async {
_appId = appId;
_prefs = await SharedPreferences.getInstance();
_token = _prefs.getString('token');
_isInit = true;
await _setToken(_token);
}