controllerapp

controller.dart

import 'package:get/get.dart';

class MyController extends GetxController{
  var count = 0.obs;
  void increment(){
    count++;
  }
}

main.dart

import 'package:flutter/material.dart';
import 'package:get/get.dart';
import 'package:controllerapp/controller.dart';

void main() {
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  //MyController controller = Get.put(MyController());
  @override
  Widget build(BuildContext context) {
    return GetMaterialApp(
      home: Scaffold(
        body: Center(
          child: Column(
            children: <Widget>[
              GetX<MyController>(
                init: MyController(),
                builder: (controller){
                  return Text(
                    'value is ${controller.count}',
                    style: TextStyle(
                      fontSize: 32,
                      color: Colors.black,
                    ),
                  );
                },


              ),
              ElevatedButton(
                onPressed: (){
                  //or you have to create on top
                  //MyController controller = Get.put(MyController());
                  Get.find<MyController>().increment();
                },
                child: Text('click'),
              )
            ],
          ),
        ),
      ),
    );
  }
}