Flutter: Singleton data, getter called on null

Question

after I've retrieved data (an user) from an http request, I want to put this data into a singleton. Then, in another view, I want to show the name of this user in the sidebar, but it says "The getter 'user' was called on null." Here's my code:

var user = await getUser(_username, _password);

      if (user.loginError == false){
        model.user = user;

        Navigator.of(context).pushNamedAndRemoveUntil(
            '/home_view', ModalRoute.withName('/home_view'));
       }

And here's when I try to use the user.name:

Widget hamburgerMenu() {
  Model model;
  return new Drawer(
    child: ListView(
      children: <Widget>[
        new UserAccountsDrawerHeader(
          accountName: Text(model.user.name,
            ...

You shouldn't use singletons in flutter. Instead use inheritedWidgets. See https://stackoverflow.com/questions/49491860/flutter-how-to-correctly-use-an-inherited-widget/49492495#49492495 — Rémi Rousselet, Sep 13 '18 at 18:35
When their value changes, widgets that depends on it are not automatically reloaded. Inheritedwidgets are there to solve this situation. They are basically singletons that reload widgets that depends on it — Rémi Rousselet, Sep 14 '18 at 06:32
But if I never want to change these item, I think I could also use a singleton, don't I? — Little Monkey, Sep 14 '18 at 06:36
Not saying you can't, but it's a bad practice. What if you want to handle disconnection or renaming the user for example? — Rémi Rousselet, Sep 14 '18 at 06:57

score 2 · Accepted Answer · answered Sep 13 '18 at 20:38

In hamburgerMenu() you are declaring the Model model; but you never asign any value to it. It will always be null. If it's a singleton you need to do something like this

Widget hamburgerMenu() {
  Model model = Model.instance;//You fetch the instance of the singleton
  return new Drawer(
    child: ListView(
      children: <Widget>[
        new UserAccountsDrawerHeader(
          accountName: Text(model.user.name,
            ...

Also, don't do this inside the build function. If it's a stateful widget do it in the initState() function

oooh yes, Didn't notice my mistake. Thanks a lot! – Little Monkey Sep 14 '18 at 06:22 — Little Monkey, Sep 14 '18 at 06:22

Flutter: Singleton data, getter called on null

1 Answers1