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Learn how to notify `app.component` in Angular about user login/logout events and implement dynamic UI changes using a service for better user experience.
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This video is based on the question https://stackoverflow.com/q/74346041/ asked by the user 'Arvind Chourasiya' ( https://stackoverflow.com/u/8977696/ ) and on the answer https://stackoverflow.com/a/74346272/ provided by the user 'Octavian Mărculescu' ( https://stackoverflow.com/u/1440005/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Dynamically Update UI in Angular Based on User Login State

When building a web application in Angular, you often need to keep track of whether a user is logged in or logged out. This is crucial for displaying the appropriate UI elements, such as navigation bars. In this guide, we will explore how you can let your app.component know when a user logs in or out, allowing you to update the UI dynamically based on user authentication status.

The Problem

Typically, the app.component initializes first and shows the navigation bar based on the user's authentication state. When the user logs in, we need the app.component to be aware of this change, so it can display a different navigation bar (Navigation Bar # 2, for instance) compared to when the user is logged out (Navigation Bar # 1).

Here is a simplified code example of how the app.component.html might appear initially:

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Current Implementation

In our current setup, we are checking local storage for the isloggedin state within the app.component.ts constructor:

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However, the major challenge here is making sure that when localStorage’s isloggedin variable changes, the app.component is updated as well.

The Solution: Using a Service for State Management

To solve this problem efficiently, we can utilize an Angular service to manage the isLoggedIn state. This allows various components to subscribe to changes in the login status without directly inspecting the local storage.

Step 1: Create a Login Service

First, we'll create a new service named LoginService that will manage the logged-in state.

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Step 2: Update the Login Component

Next, we need to inject the LoginService into our login component to update the global login status when the user logs in or logs out.

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Make sure to also call this.loginService.updateLoggedInStatus(false); in your logout method.

Step 3: Modify the App Component

Now we’ll enhance the app.component to listen to changes in the login status. Instead of using a simple boolean property, we will utilize an observable.

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

Step 4: Update the Template with Async Pipe

Finally, we will modify the template of the app.component to use the async pipe, allowing it to react automatically to state changes.

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

Conclusion

By leveraging a service to manage the user's authentication state, we can efficiently update the UI in the app.component based on the login status. This approach not only ensures that the components remain decoupled but also enhances user experience by providing a responsive UI.

Now you have a robust solution for dynamically managing user login state in your Angular applications. Happy coding!