Validating a checkbox -- after

Register.dart

Widget get _buildAgreeToTermsField {
  // TODO 8: Wrap the Column with a FormField<bool>
  return FormField<bool>(
    // 1
    initialValue: _agree,
    // 2
    builder: (FormFieldState<bool> state) {
      return Column(
        children: <Widget>[
          Row(
            children: <Widget>[
              Checkbox(
                // 3
                value: state.value,
                onChanged: (bool val) => setState(() {
                  // 4
                  _agree = val;
                  // 5
                  state.didChange(val);
                }),
              ),
              const Text("I agree to the terms."),
            ],
          ),
          // 6
          state.errorText == null
          ? Text("")
          : Text(state.errorText, style: TextStyle(color: Colors.red)),
        ],
      );
    },
    // 7
    validator: (val) => _validateTerms(_agree),
  );
}