Getting error on TextFieldEditingController - flutter

Question

I want to add textfield that has its own unique index. So I declared a list of TextFieldEditingController and call it in the Wrap(). controllers.add(TextEditingController()),. But I am getting this error while calling it. I am getting this error This expression has a type of 'void' so its value can't be used. Try checking to see if you're using the correct API; there might be a function or call that returns void you didn't expect. Also check type parameters and variables which might also be void..
List<TextEditingController> controllers = [];
Wrap(
children: retrieveData.map((order) {
return Row(
children: [
Expanded(
child: Card(
child:
SvgPicture.asset('assets/toiletpaper.svg')),
),
Expanded(
flex: 2,
child: Padding(
padding: const EdgeInsets.all(8.0),
child: Column(
crossAxisAlignment: CrossAxisAlignment.start,
mainAxisSize: MainAxisSize.min,
children: [
CustomText(
text: order.commodityName.toString()),
CustomText(text: '60 rolls per pack'),
SizedBox(
height: screenHeight(context) / 40,
),
controllers.add(TextEditingController()), // this is the error
Flexible(
child: TextFormValidator(
fillColor: Colors.white,
contentPadding:
EdgeInsets.symmetric(vertical: 8),
outlineInputBorder: OutlineInputBorder(),
controller: description,
textAlign: TextAlign.left),
)
],
),
),
)
],
);
}).toList()),

Answer 1

The line causing the error is just an expression: controllers.add(...) returns void. You placed that line inside of the children: [...] list, which has the type List<Widget>.
That's why this doesn't work:
children: [CustomText(...), CustomText(...), controllers.add(...), Flexible(...)]
^ Widget ^ Widget ^ void ^ Widget
I don't understand entirely what you are trying to achieve, that's why I can't give you a working solution, but maybe this will work:
Wrap(
children: retrieveData.map((order) {
controllers.add(TextEditingController()) // move the line here
return Row(
children: [
...
]
);
}).toList(),
)

Answer 2

the children property of the Column widget is just a List<Widget>, so it accepts only the actual flutter widget to be set inside of it, in your code, by doing the:
SizedBox(
height: screenHeight(context) / 40,
),
controllers.add(TextEditingController()),
//...
you're trying just to put another type than what is accepted from the children property, the add() method do just add elements to a List which is the controllers list and doesn't really return a Widget, it has a type of void, so the error is thrown.
you will need to take it and put it in a scope that accepts calling method (add()), like build() function scope, a lifecycle method such initState(), or even wrapping a widget with a Builder widget then call it inside the builder property.. :
Widget build() {
controllers.add(TextEditingController()),
// Your widget here
}