I am using the following package https://pub.dev/packages/get. Do I need to close my .obs in the onClose of a GetxController? I can't find anything about this in the docs. And looking at my memory it appears that the are being destroyed automatically.

In my understanding of GetX + Flutter so far...

No, you shouldn't have to remove .obs in the close() method of GetxControllers. Disposal of observables from a Controller are done automatically when the Controller is removed from memory.

GetX disposes/removes GetxControllers (and their observables) when the widget in which they are contained are popped off the widget stack / removed from the widget tree (by default, but can be overridden).

You can see this in the override of dispose() methods of various Get widgets.

Here's a snippet of dispose() that's run when GetX widgets are popped/removed:

  @override
  void dispose() {
    if (widget.dispose != null) widget.dispose(this);
    if (isCreator || widget.assignId) {
      if (widget.autoRemove && GetInstance().isRegistered<T>(tag: widget.tag)) {
        GetInstance().delete<T>(tag: widget.tag);
      }
    }
    subs.cancel();
    _observer.close();
    controller = null;
    isCreator = null;
    super.dispose();
  }

When you use Bindings or Get.to() you're using GetPageRoute's which do cleanup by Route names:

  @override
  void dispose() {
    if (Get.smartManagement != SmartManagement.onlyBuilder) {
      WidgetsBinding.instance.addPostFrameCallback((_) => GetInstance()
          .removeDependencyByRoute("${settings?.name ?? routeName}"));
    }
    super.dispose();
  }

Test App

Below is a test App you can copy/paste into Android Studio / VSCode and run to watch the debug or run window output for GETX lifecycle events.

GetX will log the creation & disposal of Controllers in and out of memory.

The app has a HomePage and 3 ChildPages using Get Controllers in 3 ways, all which remove itself from memory:

1. GetX / GetBuilder
2. Get.put
3. Bindings

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

void main() {
  // MyCounterBinding().dependencies(); // usually where Bindings happen
  runApp(MyApp());
}

class MyApp extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return GetMaterialApp(
      title: 'GetX Dispose Ex',
      home: HomePage(),
    );
  }
}

class HomePage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('GetX Dispose Test'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            RaisedButton(
              child: Text('GetX/Builder Child'),
              onPressed: () => Get.to(ChildPage()),
            ),
            RaisedButton(
              child: Text('Get.put Child'),
              onPressed: () => Get.to(ChildPutPage()),
            ),
            RaisedButton(
              child: Text('Binding Child'),
              onPressed: () => Get.to(ChildBindPage()),
            ),
          ],
        ),
      ),
    );
  }
}

/// GETX / GETBUILDER
/// Creates Controller within the Get widgets
class ChildPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: Text('GetX Dispose Test Counter'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Text('This is the Child Page'),
            GetX<ChildX>(
              init: ChildX(),
              builder: (cx) => Text('Counter: ${cx.counter}', style: TextStyle(fontSize: 20),),
            ),
            GetBuilder<ChildX>(
              init: ChildX(),
              builder: (cx) => RaisedButton(
                child: Text('Increment'),
                onPressed: cx.inc,
              ),
            ),
          ],
        ),
      ),
    );
  }
}

/// GET.PUT
/// Creates Controller instance upon Build, usable anywhere within the widget build context
class ChildPutPage extends StatelessWidget {
  //final ChildX cx = Get.put(ChildX()); // wrong place to put  
  // see https://github.com/jonataslaw/getx/issues/818#issuecomment-733652172

  @override
  Widget build(BuildContext context) {
    final ChildX cx = Get.put(ChildX());
    return Scaffold(
      appBar: AppBar(
        title: Text('GetX Dispose Test Counter'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Text('This is the Child Page'),
            Obx(
              () => Text('Counter: ${cx.counter}', style: TextStyle(fontSize: 20),),
            ),
            RaisedButton(
              child: Text('Increment'),
              onPressed: cx.inc,
            )
          ],
        ),
      ),
    );
  }
}

class MyCounterBinding extends Bindings {
  @override
  void dependencies() {
    Get.lazyPut(() => ChildX(), fenix: true);
  }
}

/// GET BINDINGS
/// Normally the MyCounterBinding().dependencies() call is done in main(),
/// making it available throughout the entire app.
/// A lazyPut Controller /w [fenix:true] will be created/removed/recreated as needed or
/// as specified by SmartManagement settings.
/// But to keep the Bindings from polluting the other examples, it's done within this
/// widget's build context (you wouldn't normally do this.)
class ChildBindPage extends StatelessWidget {
  @override
  Widget build(BuildContext context) {
    MyCounterBinding().dependencies(); // just for illustration/example

    return Scaffold(
      appBar: AppBar(
        title: Text('GetX Dispose Test Counter'),
      ),
      body: Center(
        child: Column(
          mainAxisAlignment: MainAxisAlignment.spaceEvenly,
          children: [
            Text('This is the Child Page'),
            Obx(
                  () => Text('Counter: ${ChildX.i.counter}', style: TextStyle(fontSize: 20),),
            ),
            RaisedButton(
              child: Text('Increment'),
              onPressed: ChildX.i.inc,
            )
          ],
        ),
      ),
    );
  }
}


class ChildX extends GetxController {
  static ChildX get i => Get.find();
  RxInt counter = 0.obs;

  void inc() => counter.value++;
}

Notes

Get.to vs. Navigator.push

When using Get.put() in a child widget be sure you're using Get.to() to navigate to that child rather than Flutter's built-in Navigator.push.

GetX wraps the destination widget in a GetPageRoute when using Get.to. This Route class will dispose of Controllers in this route when navigating away / popping the widget off the stack. If you use Navigator.push, GetX isn't involved and you won't get this automatic cleanup.

Navigator.push

onPressed: () => Navigator.push(context, MaterialPageRoute(
                  builder: (context) => ChildPutPage())),

Get.to

onPressed: () => Get.to(ChildPutPage()),