Setting provider state in InitState gives error

Question

How can I set a provider in the initState method? Tried doing listen: false but got an error:

final MyProvider myProvider = Provider.of<MyProvider>(context, listen: false);
if (myProvider.someVar == null) {
    myProvider.setSomeVar('yo');
}

I get the following error:

setState() or markNeedsBuild() called during build

Here's the providers method

void setSomeVar(String text) {
    someVar = text;
    notifyListeners();
  }

In your Provider, setSomeVar() is calling notifyListeners(). This is a no-no in initState an build(). Try using a addPostFrameCallback to setSomeVar() after the build is complete. — JonnyH, Sep 07 '20 at 19:36
Review this question and see if it applys to your code as well... https://stackoverflow.com/questions/58584334/understand-how-listen-false-works-when-used-with-providersometype-ofcontext — JonnyH, Sep 07 '20 at 19:50
Ah. Are you calling provider.of() “outside” of your build method? — lenz, Sep 07 '20 at 19:50
M ore information here.. https://stackoverflow.com/questions/60250572/provider-changenotifier-set-state-after-widget-is-build?rq=1 — JonnyH, Sep 07 '20 at 19:54
To the best of my understanding, listen false setting prevents rebuilds when the value changes. But your provider still needs the build context — lenz, Sep 07 '20 at 19:54
@lenz So would it make sense to call the provider in the build method? `Provider.of(context, listen: false)` — Jessica, Sep 07 '20 at 19:56
Yes 100%. This would update the value but without forcing a rebuild of the widget’s UI — lenz, Sep 07 '20 at 19:58
There is a workaround, but it’s a bit complex, it’s probably way easier just to review the logic in your code and use provider in the build method. But for reference it involves extracting context outside of the build method. — lenz, Sep 07 '20 at 20:01
You’re getting the same error wih the provider inside of your build method? — lenz, Sep 07 '20 at 20:10

JonnyH · Accepted Answer · 2020-09-08T02:41:30.263

In your Provider, setSomeVar() is calling notifyListeners(). This is a no-no in initState and build(). Try using a addPostFrameCallback to setSomeVar() after the build is complete.

Also, when using addPostFrameCallback, for something that uses context, you should check for context == null as a precaution.

initState() {
  WidgetsBinding.instance.addPostFrameCallback((_) {
    if (context == null) return;
    log('Navigating to SplashPage');
    Navigator.pushReplacementNamed(context, splashRoute);
  });
  
  super.initState();
}

Setting provider state in InitState gives error

1 Answers1