Flutter app variables reset each time you leave the page - flutter

Question

I'm making a flutter app. Each time I leave the page, the variables reset. How do I make it so that the data stays the same, even if you leave the page? I'm using getx for state management. Here is my code:
//Button that leaves the page
Align(
alignment: Alignment.topLeft,
child: IconButton(
onPressed: () => Get.back(),
icon: const Icon(Icons.arrow_back),
),
),
When you click the button, it leaves the page and resets the variable maintasks shown here.
Align(
alignment: Alignment.topLeft,
child: Padding(
padding: const EdgeInsets.only(left: 25.0),
child: Text(
maintasks,
style: const TextStyle(
fontSize: 23,
color: Colors.black,
fontWeight: FontWeight.w800,
),
),
),
),
There is a function which changes the variable maintasks to the user input. However this user input is reset each time you leave the page. I've tried using SetState to save the variable but for some reason it doesn't work.
Sorry if my question is worded badly. If anyone knows how to do this, please tell me. Thanks in advance.

Answer 1

Widget state is reset as soon as the widget is disposed.
For this, using GetX, you could use GetXControllers
Example, let's imagine you need a state that's composed by a username and a password,
class LoginController extends GetxController {//GetxController comes from Getx package
var username = ''.obs;//creates a stream that can be listened from the UI, whose value is a String
var password = ''.obs;//same here
void onUsernameChanged(String newValue) {
username(newValue);//changes username stream last value to newValue's
}
void onPasswordChanged(String newValue) {
password(newValue);//the same
}
}
Now, you must insert an instance of this controller in your widget tree before the widget is built (For example, in initState)
#override
void initState() {
_controller = Get.put<LoginController>(LoginController());
super.initState();
}
Once you know you have this instance in the widget tree, you just listen to its streams using GetX widget
GetX<LoginController>(
builder: (controller)=>Text(controller.username.value)
)//this guy will repaint every time username changes
This is important because the instance of this widget will remain alive in the widget tree until either the app ends or the controller is explicitly deleted