Fixing CalledFromWrongThreadException When Updating TextView in Kotlin Using Coroutines

Описание: Learn how to correctly use Kotlin Coroutines to update your UI components like TextView without crashing your Android application.
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This video is based on the question https://stackoverflow.com/q/65879622/ asked by the user 'Yurowitz' ( https://stackoverflow.com/u/14910363/ ) and on the answer https://stackoverflow.com/a/65879860/ provided by the user 'Ashique Bava' ( https://stackoverflow.com/u/14280831/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding the CalledFromWrongThreadException in Kotlin

As a newcomer to Kotlin programming, you might encounter several challenges as you dive deeper into Android development. One of the frequent problems that developers face is the CalledFromWrongThreadException, which arises when trying to manipulate UI elements from a background thread instead of the main (UI) thread.

This error is especially common among developers using Kotlin Coroutines for asynchronous programming. If you are attempting to update a TextView within a fragment after performing a task, such as clicking a button, it’s crucial to understand how to properly manage threads in your application.

The Problem: UI Updates Causing Crashes

In the case presented, the developer attempted to update a TextView every second after a button click using a Coroutine. However, the app crashed with the following error message:

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

This error indicates that the code attempting to update the UI is being executed on a background thread instead of the main thread. Let’s take a look at the problematic code:

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

The Solution: Updating UI on the Main Thread

To resolve the CalledFromWrongThreadException error, it is essential to switch the dispatcher to Dispatchers.Main, which will ensure that your TextView updates are executed on the main UI thread. Here's how you can modify your code:

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

Breakdown of the Updated Code:

GlobalScope.launch: Initiates a Coroutine in the global scope, which is a common approach for quick tasks, but should be used cautiously to avoid memory leaks.

for loop: Iterates from 1 to 10, incrementing the pingCount variable.

Async UI Update: By creating a nested GlobalScope.launch(Dispatchers.Main) block, you specify that the following code within that block is intended to run on the main thread.

Delay: The delay(1000) function pauses the Coroutine for 1 second between updates.

Best Practices for Using Kotlin Coroutines

Do Not Use GlobalScope: It's better to use lifecycleScope or viewModelScope provided by Android to manage the Coroutine's scope, thus preventing potential memory leaks.

Error Handling: Always consider adding error handling around your Coroutine to catch any exceptions gracefully.

Limit the Number of Active Coroutines: For performance reasons, avoid too many nested Coroutines which can cause overhead. Instead, structure your logic to handle state updates more efficiently.

Conclusion

By ensuring that UI updates are executed on the main thread using Dispatchers.Main, you can prevent the CalledFromWrongThreadException error while utilizing Kotlin Coroutines effectively. This approach is essential for smooth and responsive Android applications.
With a better understanding of threading in Kotlin, you can now confidently update your UI without crashing your app.

Now that you have a grasp of these concepts, happy coding!