GlobalKey<FormState> validation on press code example

Example 1: create a validator in flutter

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

Example 2: create a validator in flutter

ElevatedButton(
  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'),
);