I want to use Provider in InitState() but got an exception: Null check operator used on a null value-CodePudding

Hi I'm new to flutter.

I am using Provider and want to use the data I get from it as the initial value of textfield. So I decided to define the controller as a nullable value and put the text to it in initState().

Here is the code.

...
TextEditingController? _lastNameController;
TextEditingController? _firstNameController;

@override
void initState() {
  super.initState();
   WidgetsBinding.instance.addPostFrameCallback((timeStamp) {
    MyProvider myProvider = Provider.of(context, listen : false);
    _lastNameController  = TextEditingController(text : myProvider.lastName);
    _firstNameController = TextEditingController(text : myProvider.firstName);
  });
}

@override
Widget build(BuildContext context) {
  return Row(
    children : [
      // this is an extension of TextField
      MyTextField(controller : _lastNameController!,  hintText : 'Last Name'),
      const Spacer(),
      MyTextField(controller : _firstNameController!, hintText : 'First Name')
...

And I got an exception Null check operator used on a null value.

Please let me know if you have any solution.

Thanks,

CodePudding user response：

WidgetsBinding.instance.addPostFrameCallback will calls after the 1st frame is build. So initially MyTextField is getting null from both _lastNameController and _firstNameController.

You can do

 MyTextField(controller : _lastNameController??TextEditingController(),

if(_lastNameController!=null) MyTextField(controller : _lastNameController,