Скачать или смотреть How to Fix Async Pipe Not Updating View in Angular AfterViewInit

Learn why the Angular `async` pipe fails to update the view in `AfterViewInit` and how to implement solutions for effective change detection.
---
This video is based on the question https://stackoverflow.com/q/63376951/ asked by the user 'David' ( https://stackoverflow.com/u/10070613/ ) and on the answer https://stackoverflow.com/a/63376994/ provided by the user 'andsilver' ( https://stackoverflow.com/u/12364558/ ) 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: Angular - Async pipe not updating View when AfterViewInit emits a new value

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.
---
How to Fix Async Pipe Not Updating View in Angular AfterViewInit

When working with Angular, you might run into situations that seem puzzling, particularly when dealing with reactive programming and change detection strategies. One common issue developers face is related to the async pipe not updating the view when new values are emitted from the AfterViewInit lifecycle hook. In this guide, we’ll explore this issue in depth and provide you with clear solutions to ensure your view updates properly.

Understanding the Problem

Consider a simple Angular component that utilizes a BehaviorSubject to hold and emit values. You may expect that anytime a new value is pushed to the BehaviorSubject, the view should reflect this value immediately, particularly when using Angular’s async pipe in the template.

Here’s the essence of the problem:

OnInit: When you emit a value during the ngOnInit lifecycle hook, the view updates correctly.

AfterViewInit: However, if you try to emit a value post-initialization in ngAfterViewInit, the view doesn't update as expected.

This behavior can be confusing, leading developers to wonder if it’s a bug or misconfiguration.

Exploring the Solution

The reason behind this behavior lies in Angular’s change detection strategy, particularly when using the OnPush strategy. Let’s delve into the solution step-by-step.

Change Detection Strategy

OnPush Change Detection: By default, Angular checks for changes in the component hierarchy. When you use OnPush, however, Angular ignores changes unless:

An @ Input reference changes.

An event originates from the component or one of its children.

You manually trigger change detection.

Lifecycle Hooks:

ngOnInit: Called before the view is rendered, allowing changes to affect the view.

ngAfterViewInit: Fired after the initial view has been checked and rendered. Since OnPush is active, changes won't trigger a check automatically.

Implementing the Fix

To resolve the issue with the async pipe not updating the view after AfterViewInit, you can manually trigger change detection. This ensures that any updates to the view are recognized and rendered.

Here’s how to implement this:

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

Summary of Key Changes

In your ngAfterViewInit, after emitting the new value:

Add the line this.cd.detectChanges(); to manually trigger change detection. This will allow the async pipe to recognize that there has been a change and update the view accordingly.

Conclusion

By understanding the nuances of Angular’s change detection strategies and applying manual detection where necessary, you can ensure that your components behave as expected across all lifecycle hooks. Utilizing the async pipe efficiently can greatly improve the reactivity of your application, but always keep in mind how Angular manages change detection.

With the information and steps provided above, you should be well on your way to resolving the challenge of the async pipe not updating during AfterViewInit. Keep experimenting and adjusting your components to best leverage Angular's powerful features!