How to Update Angular View from an Async Function with Progress Callbacks

Learn how to effectively update your Angular view from an async function, ensuring your UI responds to real-time data changes such as loading progress.
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How to Update Angular View from an Async Function with Progress Callbacks

Initializing a model or loading data asynchronously can often present challenges, especially when it comes to updating the user interface (UI) in Angular. One common issue developers encounter is the asynchronous method not updating the view until the entire process is completed. This can lead to a frustrating user experience, especially when you want to provide real-time feedback, such as displaying loading progress.

In this post, we will address this issue specifically by exploring how to update the Angular view while waiting for an async operation to complete, using an example involving progress callbacks from the TensorFlow.js library.

The Problem

You may have an asynchronous method that utilizes a loading function, such as loading a machine learning model with TensorFlow.js. The callback provides updates on the loading progress, but the Angular view does not reflect these updates. Here’s a simplified code snippet demonstrating this issue:

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

In the example above, the progress variable gets updated, but the view doesn’t reflect these changes until the loading process is complete. This typically occurs because the change detection in Angular is not triggered inside the asynchronous onProgress function.

The Solution

To remedy this situation, you can utilize Angular’s NgZone to explicitly inform Angular’s change detection mechanism of the updates. By encapsulating your progress updates within ngZone.run(), Angular will be notified to check for any changes and update the view accordingly.

Implementation Steps

Import NgZone: Make sure to import NgZone from @ angular/core.

Inject NgZone in the Constructor: Include NgZone in your component's constructor so you can use it within your methods.

Wrap Progress Updates: Inside the onProgress callback, wrap the progress assignment in ngZone.run(). This ensures that Angular’s change detection is triggered whenever the progress updates.

Here’s the updated code:

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

Explanation of the Code Changes

NgZone Injection: By injecting NgZone, we ensure that we can control the change detection context when necessary.

Using ngZone.run(): This function allows you to execute a piece of code inside the Angular zone, thus notifying Angular to perform change detection. This ensures that whenever this.progress is updated, it immediately reflects in the UI.

Conclusion

Updating the Angular view from an async function, particularly during a loading process, can be efficiently handled by utilizing Angular's powerful NgZone. By wrapping your logic in ngZone.run(), you can ensure that your UI remains responsive and accurately reflects real-time changes, enhancing the user experience.

Next time you're working with asynchronous operations in Angular, keep this approach in mind to ensure your view stays in sync with your data!