Скачать или смотреть How to Make Angular Reactive Forms Respond on First Touch Using valueChanges

Discover how to resolve the issue of Angular Reactive Forms responding only on the second touch of a mat-select by understanding the proper structure for `valueChanges` and event handling.
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This video is based on the question https://stackoverflow.com/q/74449447/ asked by the user 'Yoni' ( https://stackoverflow.com/u/9088906/ ) and on the answer https://stackoverflow.com/a/74449567/ provided by the user 'MoxxiManagarm' ( https://stackoverflow.com/u/11011793/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Make Angular Reactive Forms Respond on First Touch Using valueChanges

If you're working with Angular Reactive Forms and have encountered the frustrating issue where the valueChanges only responds after the second interaction, you're not alone. This is a common challenge among developers, especially when utilizing components like mat-select within a FormArray. Before we look into how to solve this, let’s break down the situation and then explore the solution methodically.

The Challenge You’re Facing

In your current implementation, you are using a mat-select control within a FormArray. The goal is to trigger the valueChanges event and execute a function to fetch data based on the selected value. However, you've noticed that the doSomething function only receives the new value after the second selection is made, which is not optimal for user experience.

Here’s a small snippet illustrating the issue:

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

Additionally, your HTML for the mat-select looks like this:

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

The Solution: Separating Events and valueChanges

To resolve this issue, it’s recommended to stop mixing events with valueChanges. Instead, you can choose to either manage events through (selectionChange) or handle it via valueChanges, but not both.

Option 1: Handling SelectionChange Directly

If you prefer to react immediately when a user makes a selection, you can modify the doSomething function to fetch data without relying on the valueChanges observable:

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

In this way, each time a selection is made, the data fetching occurs without waiting for a subsequent trigger.

Option 2: Utilizing valueChanges Efficiently

If you still want to leverage valueChanges for other purposes, set it up once during the initialization of your form. The recommended approach is to subscribe to valueChanges in the ngOnInit() lifecycle method like this:

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

This will ensure that any change in the selected value from the mat-select is handled correctly from the first interaction.

Conclusion

By separating the concerns of event handling and subscription to valueChanges, you can enhance the responsiveness of your Angular Reactive Forms. Choose the method that aligns with your use case, whether it’s directly reacting to selection changes or setting up an observable for continuous monitoring. Either way, these adjustments will significantly improve user experience and application efficiency.

With these tips in mind, you can now ensure that your Angular forms respond accurately and promptly, making your application smoother and more intuitive for users.