main.dart

var retrievedName;          

            ElevatedButton(
              onPressed: () {
                ref.child("Name").once().then((DataSnapshot data){
                  print(data.value);
                  print(data.key);
                  setState(() {
                    retrievedName = data.value;
                  });
                });
              },
              child: Text("Get"),
            ),
            Text(retrievedName ?? ""),