A MixViewObserverState was used after being disposed

[rjahn]

If you do a manual animateTo(context, index) and change the page/show different widgets before the animation is done, following error will be logged:

The following assertion was thrown during a scheduler callback:
A MixViewObserverState was used after being disposed.

Once you have called dispose() on a MixViewObserverState, it can no longer be used.
When the exception was thrown, this was the stack: 
#0      MixViewObserverState._debugAssertNotDisposed.<anonymous closure> (package:scrollview_observer/src/sliver/sliver_observer_view.dart:160:9)
#1      MixViewObserverState._debugAssertNotDisposed (package:scrollview_observer/src/sliver/sliver_observer_view.dart:166:6)
#2      MixViewObserverState._notifySliverListeners (package:scrollview_observer/src/sliver/sliver_observer_view.dart:418:12)
#3      MixViewObserverState.handleContexts (package:scrollview_observer/src/sliver/sliver_observer_view.dart:195:5)
#4      ObserverWidgetState._setupSliverController.<anonymous closure> (package:scrollview_observer/src/common/observer_widget.dart:368:7)
#5      ObserverControllerForScroll._handleScrollEnd.<anonymous closure> (package:scrollview_observer/src/common/observer_controller.dart:1169:38)
#6      SchedulerBinding._invokeFrameCallback (package:flutter/src/scheduler/binding.dart:1442:15)
#7      SchedulerBinding.handleDrawFrame (package:flutter/src/scheduler/binding.dart:1369:11)
#8      SchedulerBinding._handleDrawFrame (package:flutter/src/scheduler/binding.dart:1208:5)
#9      _invoke (dart:ui/hooks.dart:316:13)
#10     PlatformDispatcher._drawFrame (dart:ui/platform_dispatcher.dart:428:5)
#11     _drawFrame (dart:ui/hooks.dart:288:31)

I have no simple demo application for you, but I hope it's clear what's happening?

[Vlsrnd]

The same issue. Let me clarify that it appears when you navigate back while the scroll animation is not finished. It doesn't matter whether via a animateTo or manually scroll.
You can reproduce it using the example NestedScrollViewDemoPage from the repository. Launch, scroll, and while scrolling, change the page so that the dispose method is called.

[rjahn]

I fixed the problem temporary, but it's not the best solution 🤗

class FixMixViewObserverState extends MixViewObserverState {

    @override
    SliverObserverHandleContextsResultModel<ObserveModel>? handleContexts({
      bool isForceObserve = false,
      bool isFromObserveNotification = false,
      bool isDependObserveCallback = true,
      bool isIgnoreInnerCanHandleObserve = true,
    }) {
      //means: disposed
      if (innerSliverListeners == null) {
        return null;
      }

      return super.handleContexts(
        isForceObserve: isForceObserve,
        isFromObserveNotification: isFromObserveNotification,
        isDependObserveCallback: isDependObserveCallback,
        isIgnoreInnerCanHandleObserve: isIgnoreInnerCanHandleObserve);
    }

  }