Implementing Constructor Injection in Angular Components

Constructor injection is a fundamental design pattern in Angular that promotes testability, reusability, and maintainability by providing dependencies to a component through its constructor. This challenge will guide you through creating an Angular component that utilizes constructor injection to receive a service, demonstrating a best practice for dependency management.

Problem Description

You are tasked with creating a simple Angular component called DataDisplayComponent that displays data fetched from a service called DataService. The DataDisplayComponent should receive an instance of DataService via constructor injection. The component should then call a method on the DataService to retrieve data and display it in the component's template. The goal is to demonstrate how to properly inject a service into a component's constructor, allowing for easy testing and decoupling.

Key Requirements:

• Create a DataService that has a method called getData() which returns a Promise resolving to an array of strings. For simplicity, the data can be a hardcoded array of strings.
• Create a DataDisplayComponent that injects the DataService into its constructor.
• In the component's ngOnInit lifecycle hook, call getData() on the injected DataService.
• Store the retrieved data in a component property.
• Display the data in the component's template using *ngFor.

Expected Behavior:

When the component loads, it should fetch data from the DataService and display it in a list. If the DataService encounters an error, the component should display an error message.

Edge Cases to Consider:

• What happens if the DataService throws an error? The component should handle this gracefully and display an appropriate error message.
• Consider the asynchronous nature of the getData() method. Ensure the component waits for the data to be fetched before attempting to display it.

Examples

Example 1:

Input: DataService.getData() returns ["Item 1", "Item 2", "Item 3"]
Output: The DataDisplayComponent template displays a list:
<ul>
  <li>Item 1</li>
  <li>Item 2</li>
  <li>Item 3</li>
</ul>
Explanation: The component successfully fetched the data and rendered it in the template.

Example 2:

Input: DataService.getData() throws an error.
Output: The DataDisplayComponent template displays an error message:
<p>Error fetching data.</p>
Explanation: The component correctly handled the error and displayed an error message to the user.

Constraints

• The solution must be written in TypeScript.
• The DataService should use a Promise to simulate asynchronous data fetching.
• The component should use Angular's built-in *ngFor directive to display the data.
• Error handling should be implemented to gracefully handle potential errors from the DataService.
• The solution should be modular and follow Angular best practices.

Notes

• Remember that constructor injection provides a clean and testable way to manage dependencies.
• Consider using Angular's async pipe in the template to handle the asynchronous data fetching.
• Think about how to handle potential errors from the DataService and provide a user-friendly error message.
• Focus on demonstrating the core concept of constructor injection and its benefits. No complex styling or additional features are required.