How can you properly cancel an in progress asynchronous operation in Dart, such as a network request, when it is no longer actually needed, for example because the user has already navigated away from that specific screen?

Dart's core Future type does not provide a universal built in cancellation mechanism on its own, so cancelling an in progress asynchronous operation typically requires either using a package specifically designed to support cancellation, such as one built around the CancelToken pattern commonly used with the Dio networking package, or manually tracking a boolean flag or checking whether a StatefulWidget is still actually mounted before applying the eventual result of a Future, which correctly prevents unnecessary work from continuing, or a completed result from being incorrectly applied, to a screen the user has already navigated away from.

final cancelToken = CancelToken();
dio.get(url, cancelToken: cancelToken);

// When no longer needed
cancelToken.cancel('Screen was disposed');