How to auto cancel UseCase job when the ViewModel is destroyed

[rommansabbir]

I want to auto cancel all UseCase request that is tied to the ViewModel.

For now: I have reigstered a callback for ViewModel.onCleared() event. So when the onCleared() is called, the callback will be invoked.

class BaseViewModel : ViewModel(){
    internal var onClearedListener : () -> Unit ={}
    override fun onCleared() {
        super.onCleared()
        onClearedListener.invoke()
    }
}

For UseCase: I have defined two more functions, cancelJob() and monitorViewModelLifecycle(vm: BaseViewModel) and added another overloading function invoke(vm: BaseViewModel,params: Params,onResult: (Either<Failure, Type>) -> Unit = {}).

abstract class UseCase<out Type, in Params> where Type : Any {
    operator fun invoke(
        vm: BaseViewModel,
        params: Params,
        onResult: (Either<Failure, Type>) -> Unit = {}
    ) {
        monitorViewModelLifecycle(vm)
        uiScope.launch { onResult(withContext(Dispatchers.IO) { run(params) }) }
    }

    //Cancel the current ongoing job
    fun cancelJob(message: String = "Abort") {
        uiScope.cancel(message)
    }

    /**
     * Monitor the [BaseViewModel] lifecycle.
     * The motto is to auto clear any ongoing job that is tied to the [BaseViewModel].
     *
     * @param vm, [BaseViewModel] instance
     */
    fun monitorViewModelLifecycle(vm: BaseViewModel) {
        vm.onClearedListener = {
            cancelJob()
        }
    }
}

So, When the ViewModel.onClearedListener is invoked I'm cancelling the current Job.

Is there any better to way to acheive this?

[crjacinro]

I feel that this code is redundant. You can make use of the viewModelScope as the ui scope for the job. It will get cancelled automatically when the view model is onCleared().

[rommansabbir]

Yes, we can make use of viewModelScope but stil in some cases I might not execute UseCase from ViewModel, I might execute it from Activity, So I wanted the Coroutine Scope & Job should be under the UseCase from where I can control them instead of passing the Coroutine Scope via params to UseCase.

[crjacinro]

If you are accessing the use case from an Activity then, you are not adhering to Clean-Architecture principles. Activities should not have access to use cases but only depend on events/data from a ViewModel

[rommansabbir]

Yes, I completely agree with you.