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Discover how to fix the `IllegalMonitorStateException` when updating `MutableLiveData` in your Android application with proper patterns and practices.
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This video is based on the question https://stackoverflow.com/q/64842032/ asked by the user 'KingFish' ( https://stackoverflow.com/u/145129/ ) and on the answer https://stackoverflow.com/a/64844834/ provided by the user 'Sergey Melnik' ( https://stackoverflow.com/u/13819675/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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Understanding and Resolving IllegalMonitorStateException in Android's MutableLiveData

When developing Android applications, especially those utilizing the MVVM architecture, developers often encounter various exceptions that can hinder the functioning of their applications. One such issue arises when attempting to update MutableLiveData in the ViewModel layer and receiving an IllegalMonitorStateException. In this guide, we will tackle this problem by first understanding what causes this exception and then discussing practical solutions to effectively handle it.

The Problem: IllegalMonitorStateException

Imagine you have set up a login feature in your application using MutableLiveData. You call an API to log the user in, and upon receiving a response, you try to notify that the data has changed with .notify(). Instead of a successful update, you face the following crash:

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Why This Occurs

The root of the issue is tied to threading and how notifications work in Java. The notify() method should only be called when you are holding the intrinsic lock for the object (in this case, MutableLiveData). Since you're calling it in the response callback after an asynchronous operation, it's not guaranteed that the thread is holding the right lock, which leads to the exception.

The Solution: Correctly Updating MutableLiveData

To resolve this issue, we need to update our approach for updating MutableLiveData. Here are two effective methods to address the problem:

1. Using Callback Functions

Instead of relying on the notify() method, you can pass a callback function to the loginUser() method. This approach ensures that you stay in the right context when handling the response and updating your LiveData. Here's how it can be implemented:

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2. Using Synchronous Calls with execute()

If you require immediate updates without callbacks, you might consider using the execute() method for synchronous requests. However, this demands running the request on a separate thread to avoid blocking the main UI thread. Here’s a brief outline of how this can be done:

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Conclusion

By leveraging callback functions or intelligently utilizing synchronous requests in another thread, you can effectively avoid the IllegalMonitorStateException and handle MutableLiveData updates gracefully. Each method has its own advantages, and the choice depends on your specific requirements and design preferences.

Now that you are equipped with these solutions, you can refine your implementation of MutableLiveData without facing crashes. Happy coding!