How can I make a number counter app using textfield in flutter? - flutter

Question

import 'package:flutter/material.dart';
void main() => runApp(Spent());
class Spent extends StatefulWidget {
#override
SpentState createState() => SpentState();
}
class SpentState extends State<Spent> {
final _controller = TextEditingController();
String name = '';
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Container (
padding: const EdgeInsets.all(30.0),
child: Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(name),
TextFormField(
textInputAction: TextInputAction.done,
controller: _controller,
decoration: InputDecoration(
fillColor: Colors.black,
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(25.0),
borderSide: BorderSide(),
),
),
keyboardType: TextInputType.number
),
FlatButton(
child: Text("Enter"),
onPressed: () {
setState(() {
name = _controller.text;
});
},
)
]
)
),
)
)
)
);
}
}
Like so, I have a TextFormField. What I want my application to do is subtract the number that is currently existing using textfield. So for example if I have the number 5000, the user would type 2000 and press enter. This would make the number to 3000. How can I make this?

Answer 1

Here's a possible solution with basic error checking.
class SpentState extends State<Spent> {
final _controller = TextEditingController();
double value = 5000;
#override
Widget build(BuildContext context) {
return MaterialApp(
debugShowCheckedModeBanner: false,
home: Scaffold(
body: Container(
padding: const EdgeInsets.all(30.0),
child: Container(
child: Center(
child: Column(
mainAxisAlignment: MainAxisAlignment.center,
children: [
Text(value.toString()),
TextFormField(
textInputAction: TextInputAction.done,
controller: _controller,
decoration: InputDecoration(
fillColor: Colors.black,
border: OutlineInputBorder(
borderRadius: BorderRadius.circular(25.0),
borderSide: BorderSide(),
),
),
keyboardType: TextInputType.number),
FlatButton(
child: Text("Enter"),
onPressed: () {
//check if we can parse it
if (double.tryParse(_controller.text) == null)
return; //can't parse it
double enteredValue =
double.parse(_controller.text);
setState(() {
value -= enteredValue;
});
},
)
])),
))));
}
}