问 颤振提供者，在提供者中使用GlobalKey<FormState>的正确方法

class RegistrationPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        centerTitle: true,
        title: Text("Title"),
      body: MultiProvider(providers: [
        ChangeNotifierProvider<UserProfileProvider>.value(value: UserProfileProvider()),
        ChangeNotifierProvider<RegiFormProvider>.value(value: RegiFormProvider()),
      ], child: AllRegistrationWidgets()),
class AllRegistrationWidgets extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return GestureDetector(
      onTap: () {
        FocusScope.of(context).requestFocus(FocusNode());
      child: Container(
        child: Column(
          crossAxisAlignment: CrossAxisAlignment.stretch,
          children: <Widget>[
            Expanded(
              child: SingleChildScrollView(
                child: Column(
                  crossAxisAlignment: CrossAxisAlignment.stretch,
                  children: <Widget>[
                    SetProfilePicWidget(),
                    RegistrationForm(),
            BottomSaveButtonWidget()
class BottomSaveButtonWidget extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    final _userPicProvider =
        Provider.of<UserProfileProvider>(context, listen: false);
    final _formProvider =
    Provider.of<RegiFormProvider>(context, listen: false);
    return SafeArea(
      bottom: true,
      child: Container(
          margin: EdgeInsets.all(15),
          child: FloatingActionButton.extended(
            heroTag: 'saveform',
            icon: null,
            label: Text('SUBMIT',
                style: TextStyle(
                  fontSize: 16,
                  fontWeight: FontWeight.bold,
            onPressed: () {
               print(_userPicProvider.strImageFileName);
              _formProvider.globalFormKey.currentState.validate();
              print(_formProvider.firstName);
              print(_formProvider.lastName);
}

class RegistrationForm extends StatefulWidget {
  @override
  _RegistrationFormState createState() => _RegistrationFormState();
class _RegistrationFormState extends State<RegistrationForm> {
  TextEditingController _editingControllerFname;
  TextEditingController _editingControllerLname;
  @override
  void initState() {
    _editingControllerFname = TextEditingController();
    _editingControllerLname = TextEditingController();    
    super.initState();
  @override
  Widget build(BuildContext context) {
    final formProvider = Provider.of<RegiFormProvider>(context);
    return _setupOtherWidget(formProvider);
  _setupOtherWidget(RegiFormProvider _formProvider) {
    return Container(
      padding: EdgeInsets.all(12),
      child: Column(
        crossAxisAlignment: CrossAxisAlignment.stretch,
        children: <Widget>[
          SizedBox(height: 20),
          Text(
            'Fields with (*) are required.',
            style: TextStyle(fontStyle: FontStyle.italic),
            textAlign: TextAlign.left,
          SizedBox(height: 20),
          _formSetup(_formProvider)
  _formSetup(RegiFormProvider _formProvider) {
    return Form(
      key: _formProvider.globalFormKey,
      child: Container(
        child: Column(
          children: <Widget>[
            TextFormField(
                controller: _editingControllerFname,
                textCapitalization: TextCapitalization.sentences,
                decoration: InputDecoration(
                  labelText: "First Name *",
                  hintText: "First Name *",
                onSaved: (value) {},
                validator: (String value) =>
                    _formProvider.validateFirstName(value)),
            SizedBox(height: 15),
            TextFormField(
              controller: _editingControllerLname,
              textCapitalization: TextCapitalization.sentences,
              validator: (String value) =>
                  _formProvider.validateLastName(value),
              onSaved: (value) {},
              decoration: InputDecoration(
                labelText: "Last Name *",
                hintText: "Last Name *",
  @override
  void dispose() {
    _editingControllerFname.dispose();
    _editingControllerLname.dispose();    
    super.dispose();
}

class RegiFormProvider with ChangeNotifier {
  final GlobalKey<FormState> globalFormKey = GlobalKey<FormState>();
  String _strFirstName;
  String _strLasttName;
  String get firstName => _strFirstName;
  String get lastName => _strLasttName;
  String validateFirstName(String value) {
    if (value.trim().length == 0)
      return 'Please enter first name';
    else {
      _strFirstName = value;
      return null;
  String validateLastName(String value) {
    if (value.trim().length == 0)
      return 'Please enter last name';
    else {
      _strLasttName = value;
      return null;
}