Скачать или смотреть How to Call Another Method After Completing An Observable in Angular

Learn how to efficiently call methods after an Observable completes in Angular using RxJS techniques. This guide will help you resolve asynchronous issues and improve your application logic.
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This video is based on the question https://stackoverflow.com/q/69932287/ asked by the user 'ChennoFly' ( https://stackoverflow.com/u/15611427/ ) and on the answer https://stackoverflow.com/a/69932332/ provided by the user 'Vítor França' ( https://stackoverflow.com/u/7374524/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Call Another Method After Completing An Observable in Angular

In the world of web development, particularly when dealing with Angular and RxJS, one common challenge developers often encounter is how to properly handle asynchronous operations. If you're familiar with Observables, you probably know that they allow you to fetch data asynchronously. However, ensuring that a method dependent on that data is called at the right time can sometimes be tricky. In this post, we'll address a scenario where you need to call a method only after an Observable has completed fetching data from an API endpoint.

The Problem

Consider the case where you're working with an API that fetches a list of performances. You subscribe to the Observable returned by this API endpoint, but you also have another method that calculates costs based on the fetched data. The challenge is to ensure that this method executes only after the Observable has completed and the data is available.

Here's a quick rundown of an Angular component involved in this scenario:

[[See Video to Reveal this Text or Code Snippet]]

When you attempt to run the code above, you may notice that the calculateCosts method is never actually called. Even though you've confirmed that the Observable returns valid data, this is a common pitfall when working with Observables—especially with the finalize operator.

The Solution

The issue in your code lies in the way you're calling the calculateCosts method in the finalize operator. You need to ensure that the method is actually executed as a function. Let's break down the solution step-by-step.

Step 1: Correct the Method Invocation

In your original code, the line:

[[See Video to Reveal this Text or Code Snippet]]

does not actually call the method; rather, it refers to it without executing it. To fix this, you need to change it to:

[[See Video to Reveal this Text or Code Snippet]]

Step 2: Updated Code Example

With the proper method call in place, your updated fetchPerformances method would look like this:

[[See Video to Reveal this Text or Code Snippet]]

Step 3: Verify and Test

After making this change, be sure to re-test your component. Check the console log for the performances array output inside the calculateCosts method. It should now display the correct data once the Observable has completed.

Conclusion

Handling asynchronous data in Angular can seem daunting, especially when it comes to calling methods after an Observable completes. However, with the correct approach, you can simplify this process. By ensuring that you actually call the method you want using parentheses, you can resolve such issues efficiently.

If you follow the structured approach outlined above, you'll improve your application logic and enhance your experience with Angular and RxJS. Happy coding!