How to Preserve the Selected Value of Dynamic Options in Angular Using ngFor

A guide to fixing the issue with selecting and preserving values in Angular when options are generated dynamically using ngFor. Learn how to solve this common problem effectively.
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How to Preserve the Selected Value of Dynamic Options in Angular Using ngFor

Angular provides an amazing facility for creating dynamic forms and displaying data with the ngFor directive. However, you might encounter a tricky situation where selecting an option in one dropdown affects others. This post addresses how to save the value of an option when options are generated dynamically using ngFor in Angular.

The Problem: Losing Selected Values

Understanding the Issue

In your Angular component, you may have a list of Fixtures, each containing a list of FixtureParticipants. You are using the ngFor directive to create a dropdown list for choosing Fixture Participants. However, when you select an option in one dropdown, it causes the options in all dropdowns to change simultaneously. This results in confusion and a poor user experience. Additionally, trying to log the selected value can result in unexpected outputs such as "[Object object]" when you expected a proper representation of the selected object.

Example Code Structure

Consider the following code used in Angular to generate the dropdown options dynamically:

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

The Solution: Fixing the Dropdown Selection

Correct Usage of ngModel and ngValue

The key to solving the issue of multiple dropdowns sharing the same selected value lies in using ngValue instead of ngModel. Here’s how to implement this solution effectively:

Update your HTML
Change your option binding from [value] to [ngValue] in your <select> dropdown. This ensures that each selection retains its own value when options are generated. Here's the improved code snippet:

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

Modify the Typescript Component
Ensure that the selectedFixtureParticipant$ is properly defined and initialized without the use of the Observable type for selected participant data. Your component class would look like this:

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

Resulting Behavior

With these changes:

Each dropdown retains its selection independently of others.

The console will now log clear representations of the selected fixtureParticipant value when you utilize JSON.stringify(newValue) effectively.

Bonus Tips

Use Angular’s async pipe when dealing with Observables to automatically subscribe and unsubscribe in the template.

Utilize Angular's built-in json pipe to present objects clearly for debugging.

Conclusion

By making these adjustments, you can efficiently manage and preserve selected values within dynamically generated dropdowns in Angular applications. This simplifies user interaction and improves the overall experience. If you previously faced this issue, try implementing the above solution and witness the change in behavior!