Handling Switch between API call or Cancel previous API call and make a new one

There is the scenario when we have to switch between API calls or cancel current API call and make a new API call.

Example :
1. During pagination, you make the API call to fetch more data and then you click on some filter. Based on the filter you have to cancel previous API call and make new API call.

2. When implementing instant search i.e. when user types in a textbox and results appear in near real-time with each keystroke. So, in this case, we want to cancel previous API call

So all of you are thinking about how can we achieve this.

Photo by 胡 卓亨 on Unsplash

Thanks to SwitchMap operator

We have a SwitchMap operator.
SwitchMap should be used when only results from the last Observable matter.switchMap will subscribe to the last Observable it encounters and unsubscribes from all previous Observable.

I will take the example of a switch between API calls during pagination

Firstly I will take publishSubject ( Subject can act as both observer and observable). PublishSubject that, once an Observer has subscribed, emits all subsequently observed items to the subscriber.

PublishSubject<Boolean> filterSwitch = PublishSubject.create();

Make method in Presenter/ViewModel to set value in filterSwitch

void switchApiCall(boolean isFilterApplied) {
  filterSwitch.onNext(isFilterApplied);
}

Call this method from view/Activity based on filter status. If applied then pass true else pass false.

void subscribeToStoreSubject() {
disposable = filterSwitch.switchMap((Function<Boolean, ObservableSource<T>>) isFilterApplied -> {
        return api.fetchMoreData()})
        .subscribeOn(Schedulers.io())
        .observeOn(AndroidSchedulers.mainThread())
        .subscribe(//do your stuff );
  }
}

So Whenever a new value is pushed to filterSwitch, it cancels previous API call and makes new API call based on isFilterApplied value.
You can pass other params as well in API call based on isFilterApplied value.

Photo by One zone Studio on Unsplash

Soon I will post more articles on android, core java.
till then happy learning… :)