Скачать или смотреть Emitting Every Item from Flowable and Appending to a List Using scan in RxJava

Discover how to effectively manage emissions from a Flowable in RxJava by appending items to a list without losing earlier emitted data.
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Emitting Every Item from Flowable and Appending to a List Using scan in RxJava

RxJava has dramatically changed how we handle asynchronous data streams, especially in Android development. The challenge that many developers face is managing emissions from a Flowable. A common question that arises is: Can we set a Flowable to emit every item when it's ready and append that to a list without losing previously emitted items? In this guide, we will explore this question and provide a comprehensive solution using the scan operator in RxJava.

The Problem: Emission Management

Understanding the Scenario

You have a database query that returns a Flowable<List<ItemEntity>>. From this, you map each ItemEntity to an ItemDomain and ultimately get a Flowable<List<ItemDomain>>. However, you want to:

Receive values sequentially (e.g., have the list emit one item first, then two items, etc.)

Ensure the older emitted items are not lost in the process

Handle the emissions when the search query changes

The Solution: Using scan with Flowable

To achieve the desired functionality of appending to a list without clearing previous items, you need to use the scan operator. This operator allows you to accumulate values emitted by the flow and maintain an intermediate state of the list.

Implementation Steps:

Modify the Query Method: Use switchMap to manage the latest query result.

Utilize scan for Accumulation: This will enable you to maintain an ongoing list that receives updates.

Skip the Initial Emission: To avoid sending the empty state of the list at startup.

Here’s how you can implement this solution in Kotlin:

Sample Code

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Important Notes

Thread Management: If you plan to consume the intermediate list on a different thread, ensure that you create a copy of the list each time it is emitted. This is crucial because lists are mutable and could lead to concurrency issues.

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Database Considerations: If you're considering whether your database (e.g., Room) can return results one by one, keep in mind that you may need to implement pagination for large datasets. This would allow more efficient memory management and control over how data is loaded.

Conclusion

By using the scan operator in RxJava, you can effectively manage how a Flowable emits items sequentially while appending them to a list. This approach not only allows for real-time updates to your data as it changes but also ensures that you don’t lose previously emitted items.

Developers working with reactive programming in Android can leverage these techniques to build more responsive and well-structured applications. Happy coding!