Скачать или смотреть Resolving the Observable Issue in Angular's ngIf with the Async Pipe

Learn how to effectively utilize `Observable` with Angular's `ngIf` and async pipe to ensure your logic executes correctly.
---
This video is based on the question https://stackoverflow.com/q/64051799/ asked by the user 'Nero' ( https://stackoverflow.com/u/5053357/ ) and on the answer https://stackoverflow.com/a/64051889/ provided by the user 'Poul Kruijt' ( https://stackoverflow.com/u/3106920/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

Visit these links for original content and any more details, such as alternate solutions, latest updates/developments on topic, comments, revision history etc. For example, the original title of the Question was: Observable doesn't execute when used in ngIf

Also, Content (except music) licensed under CC BY-SA https://meta.stackexchange.com/help/l...
The original Question post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license, and the original Answer post is licensed under the 'CC BY-SA 4.0' ( https://creativecommons.org/licenses/... ) license.

If anything seems off to you, please feel free to write me at vlogize [AT] gmail [DOT] com.
---
Understanding the Observable Issue with Angular's ngIf

When working with Angular, it's common to use Observables to manage asynchronous data. However, certain scenarios, such as using an Observable with the ngIf directive, can lead to tricky issues where your code doesn’t execute as expected. In this guide, we'll address a specific problem: what to do when an observable chain inside ngOnInit doesn't execute as anticipated when controlled by a boolean observable in an ngIf condition.

The Problem

In Angular, you might attempt to control the execution of your code based on a boolean condition using an observable. Here's an example of a common scenario:

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

The Unexpected Behavior

You might face the situation where the code inside your pipe() call in ngOnInit does not execute. For instance:

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

Although you use the async pipe in the template, the contents inside the pipe() are never triggered. At first glance, this seems contradictory, as we expect the async pipe to handle subscriptions automatically.

The Solution

To resolve this issue, we need to ensure that the pipe method is properly assigned to the observable chain. Here’s how to correctly configure your ngOnInit method:

Revised Code

You should add the pipe to the observable you are declaring like this:

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

Explanation

Creating a New Observable: The key takeaway is that the pipe method creates a new Observable. The way you initially set it up, you were not storing the new observable created by pipe() on this.isAllowed$, therefore it never got subscribed to when using the async pipe in the template.

Using the Async Pipe: The async pipe does automatically subscribe to observables and thus updates the view when the data changes. However, if the observable itself is not properly created and assigned, the async pipe has no data to react to.

Conclusion

Understanding how to properly utilize Observables with Angular's ngIf and the async pipe is crucial for handling conditional rendering in your applications. By ensuring that you pipe your Observable correctly and store it, you can prevent these unexpected behaviors and allow your application to function as intended.

By following the guidelines in this post, you should be well on your way to avoiding similar problems in your Angular applications. Happy coding!