Скачать или смотреть How to Properly Retrieve LiveData on the Main Thread in Android

Learn how to effectively use LiveData in Android with MVVM architecture, ensuring data is retrieved and processed on the main thread before starting a new activity.
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This video is based on the question https://stackoverflow.com/q/63316352/ asked by the user 'WinterMute' ( https://stackoverflow.com/u/12170252/ ) and on the answer https://stackoverflow.com/a/63316831/ provided by the user 'Farid' ( https://stackoverflow.com/u/5197037/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the Problem: Retrieving LiveData on Main Thread in Android

When working with Android development, especially using Room, LiveData, and the MVVM pattern, developers may encounter challenges relating to data retrieval and UI updates. One common issue arises when trying to start an activity with data passed through an Intent after checking a condition within your data source.

In this article, we will discuss a specific problem regarding retrieving LiveData on the main thread. The issue arises when the new activity is launched before the LiveData retrieval process is complete, leading to a scenario where the required data is not yet available. Let’s break down the solution to this problem effectively.

The Code Problem

The original code snippet provided faces a timing issue. The process to retrieve additional data (in this case, activity extras) is done via a LiveData observer, but the Intent is being initialized and the new activity started too early.

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

In this example, without waiting for the LiveData to finish loading, the activity launches prematurely, resulting in missing data.

The Solution: Properly Implementing LiveData Observation

To address the problem, we need to ensure that we retrieve the data and only start the new activity after the data has been successfully loaded. Below are the steps on how to implement the solution:

Step 1: Move the startActivity Call

Instead of starting the activity right after setting up the observer, we move it inside the observer's callback. This guarantees that it is triggered only once the data retrieval is complete.

Step 2: Show Progress to the User (Optional)

While waiting for the LiveData retrieval process to complete, it is good practice to show a loading indicator, such as a progress bar, to enhance user experience. This will inform users that something is happening and prevent confusion.

Revised Code Example

Here's how the corrected code block should look:

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

Summary of Changes

Moved startActivity: The call to start the activity is now inside the observer's execution block, ensuring that it only occurs after the data has been handled.

Consider User Feedback: Optional suggestions include providing visual feedback while waiting for data retrieval (like a progress bar).

Conclusion

Retrieving LiveData on the main thread requires careful management of how and when activities are started based on whether data is available. By modifying the workflow to wait for LiveData to complete, you can prevent premature activity launching and ensure that your Intent carries the expected data. This not only improves functionality but also enhances user satisfaction with your app.

By implementing these changes, developers can effectively manage data loading and activity transitions in Android, leading to a smoother and more efficient application experience.