# Flutter Adding Two Fields Result - flutter

Question

I have created a List that stores and save multiple values and then sum it.
Now I have created another text field that stores price I wanna multiple this text field value with the list result but getting error it display null please help me out thankyou.
This is the code How I am doing sum of List
List<String> items = <String>[];
int getTotal() {
return items.fold(0, (total, item) {
int? price = int.tryParse(item);
if (price != null) {
num = total + price;
return (num);
// return total + price;
} else {
return total;
}
});
}
List
Column(
children: [
...List.generate(
items.length,
(index) => TextFormField(
keyboardType: TextInputType.number,
onChanged: (value) => items[index] = value,
decoration: InputDecoration(
hintText: items[index],
labelStyle: TextStyle(fontSize: 20.0),
border: OutlineInputBorder(),
suffixIcon: IconButton(
icon: const Icon(Icons.delete, color: Colors.red),
onPressed: () {
items.remove(items[index]);
setState(() {});
},
),
),
),
),
Then I am creating another field where I am getting price
This is how I am creating another text field which value I wanna multiply with the above list value.
Container(
margin: EdgeInsets.symmetric(vertical: 10.0),
child: TextFormField(
keyboardType: TextInputType.number,
autofocus: false,
decoration: InputDecoration(
labelText: 'Total Price: ',
labelStyle: TextStyle(fontSize: 20.0),
border: OutlineInputBorder(),
errorStyle:
TextStyle(color: Colors.redAccent, fontSize: 15),
),
controller: amountController,
validator: (value) {
if (value == null || value.isEmpty) {
return 'Please Enter Price';
}
return null;
},
),

Answer 1

This is how should your sum function should looks like:
int getMultiply() {
return multiply.fold(0, (int total, element) {
final price = int.tryParse(element);
// if price can't be parsed returns total
return total + (price ?? 0);
});
}
This is an example of text field's controller that updates global state every time it's value can be parsed to int and not equals to 0:
final TextEditingController amountController = TextEditingController()
..addListener(() {
final value = int.tryParse(amountController.text) ?? 0;
final result = value * getMultiply();
if (result > 0) {
setState(() {
// some global field that presents requested value
multiplyResult = result;
});
}
});
List of items:
Column(children: [
...List.generate(
items.length,
(index) => TextFormField(
keyboardType: TextInputType.number,
onChanged: (value) => setState(() { items[index] = value; }),
decoration: InputDecoration(
hintText: items[index],
labelStyle: TextStyle(fontSize: 20.0),
border: OutlineInputBorder(),
suffixIcon: IconButton(
icon: const Icon(Icons.delete, color: Colors.red),
onPressed: () => setState(() {
items.remove(items[index]);
}),
),
),
),
),