TextField ErrorText Will not Refresh State - dart

Question

I currently have a TextField embedded inside a SimpleDialog for entering information. The information entered needs to be validated before being used. If this validation fails, I want to show an error message using the TextField's ErrorText field. This validation occurs when the user presses a "save" button.
On fail, I update the text's value from null to "Error!". I know this is being done correctly because if I exit the SimpleDialog and then go back into the dialog, the text is updated. Clearly this is an issue with state.
Here is my code for the OnPressed method for the save button:
onPressed: () {
if (!checkDevEUICorrectness()) {
setState(() {
devEUIErrorText = "Error!";
});
}
else {
setState((){
devEUIErrorText = null;
});
}
},
And here a brief bit of code for the TextField:
new TextField(
controller: devEUIController,
decoration: new InputDecoration(
errorText: devEUIErrorText,
// This is the save button whose code is above
icon: new IconButton(...implementation...),
),
),
How should I properly be updating the state for the text? I don't see a difference in what I am doing compared to the many guides I have looked at online.

Answer 1

The code you posted dosen't help with anything but i think ik what might be the error.
When we open a SimpleDialog on a button click and try to perform something inside it.
Take care the SimpleDialog here acts as a stateless widget .
when we write
showDialog(
context: context,
builder: (BuildContext context){
return SimpeDialog(
.... // the code for deigning the simpleDialog
);
});
What you have to do is inspite of doing this .
you need to do something like this :-
showDialog(
context: context,
builder: (BuildContext context){
return DialogDemo();
});
in that DialogDemo create a stateful widget and inside that widget copy paste all the code under your main build function.
class DialogDemo extends StatefulWidget {
  DialogDemoState createState() => new DialogDemoState();
}
class DialogDemoState extends State<DialogDemo> {
  #override
  void initState() {
    super.initState();
  }
  #override
  Widget build(BuildContext context) {
return SimpleDialog(
.... // the code for deigning the simpleDialog
);
}
}