Textformfield validator

Build a form with validationflutterdev

final _formKey = GlobalKey<FormState>();

  @override
  Widget build(BuildContext context) {
    // Build a Form widget using the _formKey created above.
    return Form(
      key: _formKey,
      child: Column(
        children: <Widget>[
              // Add TextFormFields and RaisedButton here.
        ]
     )
    );
  }
}

TextFormField(
  // The validator receives the text that the user has entered.
  validator: (value) {
    if (value.isEmpty) {
      return 'Please enter some text';
    }
    return null;
  },
);

RaisedButton(
  onPressed: () {
    // Validate returns true if the form is valid, otherwise false.
    if (_formKey.currentState.validate()) {
      // If the form is valid, display a snackbar. In the real world,
      // you'd often call a server or save the information in a database.

      Scaffold
          .of(context)
          .showSnackBar(SnackBar(content: Text('Processing Data')));
    }
  },
  child: Text('Submit'),
);