calculus-use-case-operand-input.dart

class OperandInput extends StatefulWidget {
  final String label;
  final Operand operand;
  final CalculatorUseCase useCase;
  final Function onChanged;

  const OperandInput({Key key, this.label, this.operand, this.useCase, this.onChanged}) : super(key: key);

  @override
  _OperandInputState createState() => _OperandInputState();
}

class _OperandInputState extends State<OperandInput> {
  TextEditingController controller;

  @override
  void initState() {
    super.initState();
    controller = TextEditingController(text: '${widget.useCase.operandValue(widget.operand)}');
  }

  void onFromMemory() {
    if (widget.useCase.memory == null) return;
    setState(() {
      controller.text = '${widget.useCase.memory}';
    });
    widget.useCase.fromMemory(widget.operand);
    widget.onChanged();
  }

  void onChanged(String v) {
    double value = double.tryParse(v) ?? 0;
    widget.useCase.setOperand(widget.operand)(value);
    widget.onChanged();
  }

  @override
  Widget build(BuildContext context) {
    return Container(
        ...
        Flexible(child: TextField(onChanged: onChanged, ...)),
        Padding(child: RaisedButton(onPressed: onFromMemory, ...)),
    );
  }
}