snackbar not showing on button pressed

[ZeploiT]

Im trying to use this code for my project. I tried to add a notification that " printers searching" when tapping on search button. But whatever i tried is not worked for this code. I also tried to add an alerddialog but not worked again. What can i do for it?

snackbar code is here:
ScaffoldMessenger.of(context).showSnackBar(SnackBar(
content: Text('Printers Searching...'),
));