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Learn how to return a `Completable` that completes after the execution of operations in an observable chain in RxJava.
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How to Use Completable with Observables in RxJava

In the world of asynchronous programming with RxJava, we often work with Observables to handle events and data over time. A typical challenge arises when you need a Completable that signifies the completion of operations within an Observable. If you're grappling with a situation where you want your Completable to finish only after an observable's operations have completed, you’ve come to the right place!

The Problem: Handling Observables and Completables

Consider a scenario where you have an Observable that fetches objects for a user from a repository. This observable is typically used to gather data but doesn't directly signal when the associated operations are complete. Your goal is to return a Completable in the method refreshOtherObjects that completes when certain actions related to that observable are done.

Here’s the core of the problem:

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The challenge is that the Completable is not linked to the execution of the code within the subscribe block. Traditionally, the subscribe method initiates the execution but does not provide a mechanism to indicate when it has finished, resulting in a struggle to return a timely Completable.

The Solution: Using .doOnNext and .ignoreElements()

To efficiently handle this, we can use RxJava's operators to maintain the reactive pipeline properly. Instead of nesting the subscribe call, you can continue the Rx chain by performing the necessary operations inside a .doOnNext() block.

Here's how you can structure your refreshOtherObjects method:

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Breaking it Down:

Invoke the Observable:

We call getObjectsForUser() to retrieve the list of objects.

Process the Objects:

Use .doOnNext() to perform operations (like fetching and upserting other objects) on each emitted item.

Convert to Completable:

Finally, we chain .ignoreElements() to transform the observable into a Completable. This ensures that the Completable emits a completion notification once the entire operation is done.

Benefits of This Approach:

Maintains Reactive Flow: Using .doOnNext() allows you to act on the emissions without breaking the chain.

Cleaner Code: This method avoids the nested subscriptions that can make code hard to read and manage.

Easier to Reason: By following the RxJava paradigm, the code becomes more maintainable and easier to understand.

Conclusion

When working with Observables in RxJava, bridging the gap to Completable needs careful structuring of your operations. By utilizing .doOnNext() and .ignoreElements(), you can efficiently manage your asynchronous flows and signal when tasks have completed. This not only enhances readability but also keeps your code aligned with reactive principles. If you are facing issues with Completable and Observable, this approach should provide a clear and effective resolution.