Non-nullable instance field '_animationControllers' must be initialized-CodePudding

I'm using the mpin_animation plugin in flutter. I don't understand _MpinWidgetState, why it occures error. How to fix it?

error message below

Non-nullable instance field '_animationControllers' must be initialized. (Documentation) Try adding an initializer expression, or add a field initializer in this constructor, or mark it 'late'. Non-nullable instance field '_wiggleAnimation' must be initialized. (Documentation)

class _MPinWidgetState extends State<MPinWidget>
with SingleTickerProviderStateMixin {
  List<MPinAnimationController> _animationControllers;
  AnimationController _wrongInputAnimationController;
  Animation<double> _wiggleAnimation;
  String mPin = '';

  _MPinWidgetState(MPinController controller) {
    controller?.addInput = addInput;
    controller?.delete = delete;
    controller?.notifyWrongInput = notifyWrongInput;
    }

CodePudding user response：

initialise your controllers in your initState

  @override
  void initState() {
    super.initState();
    _wrongInputAnimationController = AnimationController(
      vsync: this,
      duration: Duration(your duration here),
    );
  }

CodePudding user response：

You have to initialize the fields, for example:

List<MPinAnimationController> _animationControllers = [
   ...
];

You have to give it something like 'a default value'.

By adding 'late' you can initialze them later in your code, for example in initState:

late List<MPinAnimationController> _animationControllers;

...

@override
void initState()
{
   super.initState();
   _animationControllers = [...];
}