Скачать или смотреть How to Reuse Observables Inside Functions in Angular: A Deep Dive into RxJS Techniques

Discover effective strategies for reusing Observables in Angular functions. Learn how to avoid unwanted HTTP calls, refresh data seamlessly, and manage subscriptions efficiently with RxJS.
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How to Reuse Observables Inside Functions in Angular

In Angular development, especially when dealing with data fetching and state management, reusing Observables can be both crucial and challenging. A common scenario arises when you want to refresh your data source after certain actions, like closing a flyout where a new item was created. But how do you effectively handle this without causing multiple subscriptions or unintended duplicate HTTP calls? Let’s break it down and explore some effective solutions using RxJS techniques.

The Problem

You might encounter a situation similar to the one described by a developer who was trying to create a reusable Observable for a data source that comprises a customer's list. Within an Angular component, the developer used a merge of sortChange and paginator.page Observables, along with a subscription that got triggered every time the getDataSource() function was called. This led to the following problems:

Duplicate HTTP GET requests: Every time the function was invoked, a new subscription was made, leading to multiple API calls and potentially displaying duplicate data.

Inefficient resource management: Constantly subscribing without proper unsubscription leads to memory leaks and performance degradation.

Possible Solutions

Let’s explore several strategies to address this issue:

1. Component-wide Tracking for Subscriptions

The Ugly Way: One option is to define the subscription at a component level. Checking if it's already closed before subscribing again can be a short-term fix, but it can clutter your component and isn't a clean solution.

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2. Emitting Current Values

If both your sortChange and paginator.page are Subjects, another trick could involve simply emitting their current values. This method allows a refresh without setting up a new subscription.

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While this may work, it might still be somewhat unclean.

3. Using a BehaviorSubject

A more streamlined and efficient approach involves creating a BehaviorSubject that serves as a refresh trigger for your data source. Here’s how to set it up:

Step 1: Initialize the BehaviorSubject

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Step 2: Setup Subscription to Update Handler

In your ngOnInit, set up a subscription that listens to changes in the updateHandler.

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Step 3: Trigger the UpdateHandler

Whenever a change occurs (like closing your flyout), you can simply call:

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4. Managing Lifecycle with a Subscription Subject

To further enhance this, you can implement a destroy$ subject to manage subscriptions throughout the component lifecycle. This ensures that all subscriptions are cleaned up when the component is destroyed.

Set up the Subject

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Pipe with takeUntil

In your observable pipes, use takeUntil to handle automatic unsubscription:

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Handle ngOnDestroy

Ensure to finish up properly by adding the following code to your ngOnDestroy:

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Conclusion

Handling Observables effectively in Angular is crucial for maintaining performance and a clean codebase. By employing strategies like BehaviorSubjects, managing subscriptions effectively, and ensuring proper cleanup, you can create efficient, reusable data-fetching mechanisms without encountering issues such as duplicate requests. Utilizing these techniques will not only streamline your code but also enhance the user experience by providing time