title: How to validate TextFormField individually using onFieldSubmitted
body: <p>I'm making a custom TextFormField Widget which will be used multiple times. How do I validate a single TextFormField without validating any other TextFormField that are in the same list/row/column. </p>
  
  <pre><code>Widget timeTextField (TextEditingController controller){
         return TextFormField(
           controller: controller,
           validator: (String userInput){
             if(userInput.isEmpty){return 'Need to input time';}
           },
           onFieldSubmitted: (String userInput){
             setState(() {
               debugPrint(userInput);
               controller.text = "amout";
               debugPrint(controller.text);
           });
  
     },
     );
   }
  </code></pre>
  
  <p>It validates when the user presses submit on the keyboard, if the TextFormField is empty it sends a validation error only to that TextFormField which the user pressed submit on.</p>