How to use @For with ng-template?

2 min read 25-09-2024

In Angular development, working with templates can sometimes be challenging, especially for those who are just starting to explore the framework. One common scenario developers face is the effective use of @For directives alongside ng-template. In this article, we will clarify the use of @For with ng-template, provide an example, and offer insights into its application for building dynamic and efficient user interfaces.

Original Scenario

The problem scenario presented can be summarized as follows:

How can you effectively utilize the @For directive within an ng-template in Angular to iterate over a list of items?

Revised Explanation

To answer this question effectively, we must explore how the @For directive can be leveraged within Angular's ng-template for rendering lists or collections efficiently.

Code Example

Here’s a basic code snippet demonstrating the use of @For with ng-template in Angular:

<ng-template let-item *ngFor="let item of items">
  <div>
    {{ item.name }} - {{ item.value }}
  </div>
</ng-template>

Breakdown of the Code

ng-template: This is a structural directive that allows us to define a template that can be instantiated in the UI. It is not rendered on its own but can be displayed when combined with a directive like *ngFor.
let-item: This syntax allows you to declare a variable (item in this case) for each item in the collection you are iterating over.
*ngFor: This directive is used to iterate over the items array, where items is a component property holding an array of objects (each having properties such as name and value).

Practical Example

Suppose you are building a shopping list application, and you want to display a list of products with their names and prices. You can structure your Angular component and its template as follows:

Component Code (TypeScript):

import { Component } from '@angular/core';

@Component({
  selector: 'app-shopping-list',
  templateUrl: './shopping-list.component.html',
})
export class ShoppingListComponent {
  items = [
    { name: 'Apples', value: 2.5 },
    { name: 'Bananas', value: 1.5 },
    { name: 'Cherries', value: 3.0 },
  ];
}

Template Code (HTML):

<ng-template let-item *ngFor="let item of items">
  <div>
    {{ item.name }} - ${{ item.value }}
  </div>
</ng-template>

Additional Insights

Using ng-template with *ngFor offers several advantages:

Performance: ng-template can be more efficient as it does not render elements until they are needed.
Flexibility: You can define complex structures within your template that are only instantiated when necessary.
Reusability: Define a template once and use it in various parts of your application without duplicating the code.

Best Practices

Always ensure that the array you're looping through is well-defined and populated.
Utilize trackBy function in *ngFor for better performance in larger lists to minimize rendering operations.

Conclusion

Leveraging @For with ng-template in Angular provides developers with the flexibility and efficiency needed for dynamic UI generation. As you continue to develop your Angular applications, experiment with these directives to enhance your components and user experiences.

Useful Resources

By understanding and utilizing these concepts, you can greatly improve the performance and clarity of your Angular applications. Happy coding!