The instance member 'noww' can't be accessed in an initializer

i have this date picker in my app, and i want the last date to be 3 years ago from the time using the app how can i solve it, i tried to give the last date now.year -3 but it doesn't work! it keeps tell me that 'The instance member 'noww' can't be accessed in an initializer.'

  var noww = DateTime.now();
  DateTime selectedDate = DateTime(noww.year - 3);
showDatePicker(
        context: context,
        initialDate: selectedDate, // Refer step 1
        firstDate: DateTime(now.year - 10),
        lastDate: DateTime(now.year + 1),

Declare the variable now like this

var noww;

But then after that, run the rest of the code in initState(), like this

@override
void initState(){
  super.initState();
  noww = DateTime.now();
  DateTime selectedDate = DateTime(noww.year - 3);
  showDatePicker(
    context: context,
    initialDate: selectedDate, // Refer step 1
    firstDate: DateTime(now.year - 10),
    lastDate: DateTime(now.year + 1),
  );
}

@override
Widget build(context){
  ...
}

This is because you cannot use initialisers outside of functions.