How to Properly Implement mat-list and mat-divider in Angular?

Introduction

When developing Angular applications, particularly with Angular Material, you might encounter issues regarding the mat-list and mat-divider components. Many developers wonder whether to use ngFor inside the mat-list or the mat-list-item and how to correctly place the mat-divider. Let’s delve into this topic to clarify which method is best.

Why This Issue Arises

The confusion around where to implement ngFor and the positioning of mat-divider often stems from how Angular handles component rendering. Using ngFor within the mat-list means that each item is rendered as part of the list itself; thus, the dividers are less likely to show correctly if their placement isn’t considered carefully. Conversely, applying ngFor to mat-list-item makes each list item independent and potentially isolates the divider within each item rendering.

The Correct Implementation

To implement it correctly, let’s consider both scenarios. The primary concern is ensuring that all elements appear correctly on your page. Below, I’ll provide structured examples and a definitive solution.

Example 1: ngFor on mat-list-item

Here’s the code where ngFor is applied directly to mat-list-item:

  
    

      
{{ item.title }}
      
{{ item.desc }}
      
{{ item.ad }}
    
    
  

In this implementation, every mat-list-item has its own divider, which may work, but there’s a drawback. You could end up with an extra divider at the end of your list.

Example 2: Correct Use of ngFor on mat-list

The more structured approach would be to apply ngFor to the mat-list like below:

  
    
      

        
{{ item.title }}
        
{{ item.desc }}
        
{{ item.ad }}
      
    
    
  

In this case, we’ve wrapped the mat-list-item with an ng-container. This solution avoids generating unnecessary dividers and ensures a cleaner structure.

Advantages of This Approach

• Cleaner DOM Structure: Reduces the risk of an extra divider at the end of the list.
• Easier Maintenance: Modifying the list does not affect how dividers are displayed.
• Better Styling Control: You can easily style individual list items and their dividers without overlap issues.

Frequently Asked Questions (FAQ)

1. Can I use mat-divider without mat-list?

Yes, mat-divider can be used in various components, not solely within mat-list. However, the visual context usually justifies its use within lists or similar structures.

2. What impact does placing ngFor on mat-list or mat-list-item have on performance?

Performance should not differ noticeably between the two approaches in most use cases. However, maintaining a clean and organized DOM makes your application easier to debug and enhances maintainability.

3. Why is my mat-divider not displaying correctly?

If a mat-divider is not showing, check your CSS styles to ensure nothing is overriding its default styles. Additionally, ensure it is placed correctly in relation to the list items.

Conclusion

Using ngFor effectively in Angular's mat-list requires careful attention to placement. By following the outlined structure and using ng-container, you optimize your lists for both functionality and design. Avoid placing dividers directly within the mat-list-item to maintain a seamless user experience. This best practice will enhance the performance and look of your application while leveraging Angular Material effectively.