多个选项卡上的Flutter表单currentState NoSuchMethodError：在null上调用了getter'currentState'

Question

我有一个带有3个标签栏的页面。在我的应用程序上，我有2种模式，即插入和编辑模式。在插入模式下，currentState通过表单验证绕过，但是在编辑模式下，我得到NoSuchMethodError：在null上调用getter'currentState'。我正在尝试拨打以下电话，因此我理解了这个问题：

List<dynamic> _treatment = form.fields['treatment'].currentState.value;

位于第二个标签中，而我位于第一个标签中。第三选项卡也会发生同样的情况。如果我转到第2个和第3个选项卡，然后单击“保存”按钮，则不会出错，因为创建了所有表单变量。因此，我的问题是如何绕过这种情况？当我是Flutter的新手时，我们将非常感谢您的帮助。我的应用程序的用户可以在任何选项卡上单击保存按钮。在编辑模式下，我无法阻止表单验证，因为它已在插入模式下完成。以下是我的保存部件代码：

      Future _saveForm() async {
        final form = _formKey.currentState;
        if (form.validate()) {
          //_formKey.currentState.save();
          _validate = false;
          print('saved');

          form.save();
          List<dynamic> _treatment = form.fields['treatment'].currentState.value;//this make problem as this is in tab 2
          print(_treatment);

          String treatment;
          _treatment.forEach((dynamic treat) {
            if (!treat.contains('FormBuilderFieldOption')) {
              if (treatment == null) {
                treatment = treat.toString();
              } else {
                treatment = treatment + ',' + treat.toString();
              }
            }
          });

          final int prefs = await Preference.getInt('userid');
          final int _loginUser = prefs;
          String _visithealthfacility =
              form.fields['visithealthfacility'].currentState.value.toString();
          if (_visithealthfacility == 'null') {
            _visithealthfacility = null;
          }
          String _bloodinstool = form.fields['bloodinstool'].currentState.value;
          if (_bloodinstool == null) {
            _bloodinstool = 'No';
          }
          String _fever = form.fields['fever'].currentState.value;
          if (_fever == null) {
            _fever = 'No';
          }
          String _other = form.fields['other'].currentState.value;
          if (_other == null) {
            _other = 'Disoriented';
          }
          String _ocv = form.fields['ocv'].currentState.value;//this makes 

problem as it's in tab 3
      if (_ocv == null) {
        _ocv = 'No';
      }
      final Country _country = form.fields['country'].currentState.value;
      final District _district = form.fields['district'].currentState.value;
      final Governorate _governorate =
          form.fields['governorate'].currentState.value;
      final HealthFacility _healthfacility =
          form.fields['healthfacility'].currentState.value;
      final ORT _ort = form.fields['ort'].currentState.value;
      final Village _village = form.fields['village'].currentState.value;
      final CTC _ctc = form.fields['ctc'].currentState.value;
      final CaseData _caseData = CaseData(
        id: widget.caseData.id,
        age: form.fields['age'].currentState.value,
        bloodinstool: _bloodinstool,
        comment: form.fields['comment'].currentState.value,
        countryId: _country.id,
        ctcId: _ctc != null ? _ctc.id : null,
        dehydration: form.fields['dehydration'].currentState.value,
        diarrhoea: form.fields['diarrhoea'].currentState.value,
        districtId: _district.id,
        fever: _fever,
        gender: form.fields['gender'].currentState.value,
        governorateId: _governorate.id,
        healthfacilityId: _healthfacility.id,
        hospitalization: form.fields['hospitalization'].currentState.value,
        month: form.fields['month'].currentState.value,
        ocv: _ocv,
        ortId: _ort != null ? _ort.id : null,
        other: _other,
        outcome: form.fields['outcome'].currentState.value,
        stoolsample: form.fields['stoolsample'].currentState.value,
        symptoms: form.fields['symptoms'].currentState.value.toString(),
        treatment: treatment,
        villageId: _village.id,
        visithealthfacility: _visithealthfacility,
        vomiting: form.fields['vomiting'].currentState.value,
        username: _loginUser,
        selected: 0,
      );
      print(_caseData.toString());
      _caseDataBloc.updatecaseData(_caseData);
      Navigator.pushNamed(context, '/caselist');
    } else {
      _validate = true;
      FlushbarHelper.createError(
        message: 'Mandatory fields are missing',
        title: 'Please fill the mandatory fields.',
      ).show(context);
      print('validation problem');
      setState(() {
        _autoValidate = true;
      });
    }
  }

实际上，这与代码无关，但是我认为在选项卡中处理表单状态的技术。请参阅此gif文件Video showing the problem