Error: Method ‘addPostFrameCallback’ cannot be called on ‘SchedulerBinding?’ because it is potentially null.

It could cause this problem due to flutter null-safety.

Now, your vscode or android studio should give you the errors regarding which files and which lines.

Most of the places, you will the keyword instance.

1. You need to put ! operator right next to the instance in extention_navigation.dart

      //routing.isSnackbar = true;
      SchedulerBinding.instance!.addPostFrameCallback((_) {
        controller.show();
      });

This is for snackbar. This comes from Getx package. See instance!

Another place you may get this error is get_controllers.dart. Change it like below

  void onClose() {
    WidgetsBinding.instance!.removeObserver!(this);
    super.onClose();
  }

You see instance!

In route_reporter.dart you also need to make the changes like below

  static void reportRouteDispose(Route disposed) {
    if (Get.smartManagement != SmartManagement.onlyBuilder) {
      WidgetsBinding.instance!.addPostFrameCallback((_) {
        _removeDependencyByRoute(disposed);
      });
    }
  }