Скачать или смотреть How to Properly Bind a New Object in Angular 11 Templates Using ngModel

Learn how to solve common binding issues in Angular 11 templates, specifically when working with `ngModel` and dropdown selects. Follow our step-by-step guide to ensure correct object binding.
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How to Properly Bind a New Object in Angular 11 Templates Using ngModel

When working with Angular 11, one common issue developers face is the binding of new objects in templates. You may find yourself in a situation where selecting a different object from a dropdown seems to work, but the changes aren't reflected in your component. This can be quite confusing, especially if you’re coming from AngularJS.

In this guide, we’ll explore a specific case: binding a new object from a dropdown using ngModel and ensuring that when a user makes a selection, the correct object is returned to the component.

The Problem

Imagine you have a dropdown that allows users to select different queries (objects). However, every time a user changes their selection, the default object is returned instead of the selected one. This issue arises because of how Angular manages the ngModel binding.

Here's an overview of the relevant components you'd typically have in your component.ts and component.html:

Code Overview

Component.ts

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

Component.html

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

As we can see, the approach used in the dropdown leads to confusion. Let’s address this by updating the implementation.

The Solution

To ensure that your dropdown works correctly and binds the new object to the component, you should make the following changes to your HTML code:

Revised HTML Code

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

Key Changes

Use (ngModelChange) Instead of (change)

By switching to (ngModelChange)="onQueryChange($event)", you ensure that the change event is detected after the ngModel is updated. This is crucial because the (change) event in Angular may trigger before the model has been updated, leading to inconsistencies.

Adjust the ngValue Binding

Change [ngValue]="selectedQuery" to [ngValue]="opt". This ensures that each option in the dropdown binds to the actual object in the myQueries array, not just the default selectedQuery.

Additional Context

It's important to understand the behavior of (change) and (ngModelChange):

(change): This is a vanilla JavaScript event and can be triggered at times when Angular hasn't yet updated its value, which can lead to unexpected results.

(ngModelChange): This is emitted specifically by Angular’s ngModel, ensuring that your code reacts to the updated model, not the application logic outside of Angular.

If you only need to have the correct query stored in the selectedQuery attribute without taking any additional action upon change detection, simply using the updated ngValue binding will suffice. You can remove the (ngModelChange) listener in that case.

Conclusion

By understanding the nuances of ngModel and making simple adjustments to how you bind your dropdown options in Angular 11, you can ensure your components respond correctly to user inputs. Now your selection will properly reflect changes in your component and allow for a smoother user experience.

If you found this guide helpful or have further questions, feel free to leave a comment below!