calculus-ui-scaffold-calculator-input.dart

enum Operation { addition, subtraction, division, multiplication, sqrt }

class CalculatorInput extends StatefulWidget {
  @override
  _CalculatorInputState createState() => _CalculatorInputState();
}

class _CalculatorInputState extends State<CalculatorInput> {
  final operations = <Operation, String>{
    Operation.addition: 'Addition',
    ...
  };

  Operation operation = Operation.addition;

  void onOperationChanged(Operation newOperation) {
    setState(() {
      operation = newOperation;
    });
  }

  @override
  Widget build(BuildContext context) {
    return Container(
      margin: const EdgeInsets.only(top: 10),
      child: Column(
        children: <Widget>[
          Row(
            mainAxisAlignment: MainAxisAlignment.spaceBetween,
            children: <Widget>[
              Text('Operation', style: Theme.of(context).textTheme.bodyText2),
              DropdownButton(
                value: operation,
                items: operations.entries
                    .map((entry) => DropdownMenuItem(
                        child: Text(entry.value), value: entry.key))
                    .toList(),
                onChanged: onOperationChanged,
              ),
            ],
          ),
          Operand(label: 'Operand A', initValue: 0),
          operation == Operation.sqrt
              ? SizedBox(height: 68)
              : Operand(label: 'Operand B', initValue: 0),
          Container(
              margin: const EdgeInsets.only(top: 10, bottom: 20),
              child: Text('0 + 0 = 0.000')),
        ],
      ),
    );
  }
}