Implementing an Angular App Shell for Enhanced User Experience

An app shell pattern optimizes the perceived loading speed of Angular applications by progressively loading features and data. This challenge asks you to implement a basic app shell in Angular, ensuring a minimal, functional UI is displayed quickly while the rest of the application loads in the background. This is crucial for improving user engagement and perceived performance, especially in applications with complex feature sets.

Problem Description

You need to create an Angular application with a basic app shell structure. The shell should display a loading indicator while the main application content is being fetched. Once the content is loaded, the loading indicator should disappear, and the main content should be displayed. The application content will be simulated by a delay.

What needs to be achieved:

1. Create a new Angular project (if you don't have one already).
2. Implement a ShellComponent that acts as the app shell.
3. The ShellComponent should display a loading indicator (e.g., a simple spinner) initially.
4. After a simulated delay (3 seconds), the ShellComponent should display the main application content.
5. The main application content should be a simple component displaying a message like "Application Content Loaded!".

Key Requirements:

• The loading indicator must be visible during the initial loading phase.
• The main content must be displayed only after the simulated loading delay.
• The application should be structured in a way that clearly separates the shell from the main content.
• Use Angular's built-in features for component communication and data binding.

Expected Behavior:

Upon navigating to the application, the user should immediately see the loading indicator. After 3 seconds, the loading indicator should disappear, and the "Application Content Loaded!" message should be displayed.

Edge Cases to Consider:

• What happens if the loading process takes longer than expected? (For this challenge, assume the delay is always 3 seconds, but consider this for real-world scenarios).
• How would you handle errors during the loading process? (Not required for this challenge, but a good consideration).

Examples

Example 1:

Input: User navigates to the application.
Output: A loading spinner is displayed. After 3 seconds, the spinner disappears, and the message "Application Content Loaded!" is displayed.
Explanation: The ShellComponent initially displays the loading indicator. After the simulated delay, it switches to displaying the main application content.

Example 2:

Input: Application is refreshed.
Output: The loading spinner is displayed again. After 3 seconds, the spinner disappears, and the message "Application Content Loaded!" is displayed.
Explanation: The ShellComponent resets to its initial state (loading indicator) upon refresh.

Constraints

• The simulated loading delay must be exactly 3 seconds.
• The application should be a standard Angular application (no external libraries for loading indicators are required, though you can use them if you wish).
• The solution should be well-structured and maintainable.
• The application should be functional and demonstrate the core concept of an app shell.

Notes

• Consider using Angular's async pipe for handling asynchronous operations (although not strictly required for this simple example).
• Think about how you would pass data from the shell to the main content component in a more complex application.
• This is a simplified example. Real-world app shells often involve more sophisticated loading strategies and error handling. Focus on demonstrating the fundamental principle of progressive loading.
• You can use a simple HTML spinner for the loading indicator. No need for complex CSS styling.