Cancel execution of method after it starts in Flutter - flutter

Question

Consider this method:
Future<void> methodWithAlotOfSteps()async{
callMethodA();
await callMethodB();
...
return ...;
}
which makes some computation. Suppose I want the user to be able to stop this process at any point in time (when he taps cancel button for example).
How can I stop the execution of the above method no matter what line in the method the "program counter" has reached when the user presses cancel.
I am looking for something like methodWithAlotOfSteps.cancel();.
I tried using CancelableCompleter, but even though the Future is cancelled and onCancel method of the completer is called, but the function continues execution.
I know I can set a boolean flag and check it after each "step" ("line", "call to a method"),such as :
Future<void> methodWithAlotOfSteps()async{
if(!completer.isCancelled)
callMethodA();
if(!completer.isCancelled)
await callMethodB();
...
return ...;
}
but is there a better way of doing this?

Answer 1

As #Jamesdlin suggested, the apparent way is to check the cancelable completer's state after each async gap:
class MyService{
CancelableCompleter completer = CancelableCompleter();
Future<void> doSomething() async {
doSomeSyncWork(); // Sync work
doAnotherSyncWork(); // Sync work
await doSomeAsyncWork(); // Async work, this will return control to event loop and make it possible to, for example, press a button to cancel the future.
// here we know we have lost control for a while, so we must check if we have been cancelled
if (completer.isCompleted) {
return;
}
doSomeMoreSyncWork();
await doSomeMoreAsyncWork();
// here we know we have lost control for a while, so we must check if we have been cancelled
if (completer.isCompleted) {
return;
}
...
completer.complete();
}
}