Скачать или смотреть Solving ViewContainer Issues with Angular Custom Structural Directives and *ngIf

Discover the solution to rebuilding `ViewContainers` in Angular when using custom structural directives with `*ngIf`. Learn how to effectively manage view updates with `ChangeDetectorRef`.
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This video is based on the question https://stackoverflow.com/q/65810687/ asked by the user 'cuznerdexter' ( https://stackoverflow.com/u/4594467/ ) and on the answer https://stackoverflow.com/a/65814680/ provided by the user 'cuznerdexter' ( https://stackoverflow.com/u/4594467/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem with Angular Custom Structural Directives

When working with Angular, developers often create custom structural directives to manage the visibility and rendering of components and templates dynamically. One common challenge arises when using these directives alongside *ngIf, which can lead to unexpected behavior, particularly with ViewContainer instances.

In this guide, we'll explore a specific issue where an Angular custom structural directive, namely one called permissionAccess, fails to rebuild the ViewContainer when it contains an *ngIf directive. This problem can arise in various scenarios, especially for developers manipulating views based on permission checks.

The Issue at Hand

Here's a breakdown of the reported problem:

A custom directive named permissionAccess is designed to check permissions from an NGRX store.

If no permissions are found, it clears the ViewContainer. If permissions are available, it attempts to rebuild this container using the injected TemplateRef.

Surprisingly, this process fails when any part of the HTML elements contains an *ngIf directive, leading to the ViewContainer not updating correctly.

Example Scenarios

Template that Works:

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

In this example, the directive works as intended, and the ViewContainer rebuilds without issues.

Template that Fails:

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

In this scenario, despite *ngIf being set to true, the directive fails to rebuild the ViewContainer.

The Proposed Solution

To tackle this issue, a practical approach involves ensuring the Angular change detection system is aware of updates made to the ViewContainer. This can be achieved by utilizing the ChangeDetectorRef service.

Step-by-Step Solution

Inject ChangeDetectorRef: Ensure that you inject ChangeDetectorRef into your directive’s constructor. This allows you to control change detection manually.

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

Update the ViewContainer and Trigger Change Detection: After creating the embedded view in the ViewContainer, call detectChanges() to manually trigger the change detection cycle. This will ensure that any changes are reflected in the UI.

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

Why This Works

The call to detectChanges() after manipulating the ViewContainer forces Angular to re-evaluate the view and update the UI accordingly. This should resolve any discrepancies caused by the presence of *ngIf directives, allowing for a seamless experience.

Conclusion

When working with Angular custom structural directives, particularly those interacting with *ngIf, understanding how Angular's change detection works is crucial. By integrating the ChangeDetectorRef into the flow, we can mitigate issues related to view updates and ensure that our application behaves reliably.

Feel free to dive into the code, try out these steps, and observe how your application responds. Happy coding!