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Struggling to observe `MutableLiveData` changes in Android ViewModel? This guide provides a detailed solution for observing LiveData from an Activity effectively.
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This video is based on the question https://stackoverflow.com/q/66378723/ asked by the user 'Fabrizio Ferrari' ( https://stackoverflow.com/u/1924266/ ) and on the answer https://stackoverflow.com/a/66379692/ provided by the user 'Tenfour04' ( https://stackoverflow.com/u/506796/ ) at 'Stack Overflow' website. Thanks to these great users and Stackexchange community for their contributions.

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How to Properly Observe MutableLiveData in Android ViewModel: A Guide for Beginners

As a beginner Android developer, you might encounter challenges when working with LiveData and ViewModel. One common issue is the inability to observe changes in MutableLiveData from an Activity that is owned by a ViewModel. This can be a confusing scenario, especially if initial states are observed correctly but subsequent changes don't trigger the observer. In this guide, we'll explore a typical problem faced in this context and provide a structured solution.

The Problem

Imagine a scenario where you have a Fragment associated with a ViewModel that holds a boolean value (MyMusicViewOn) defined in MutableLiveData. When you try to switch between Fragments, you want the parent Activity to observe changes in this boolean value, but it seems to not trigger the observer after the initial state. This is a frequent issue that can occur if you're not using the right instance of the ViewModel.

Code Overview

Here are snippets from your ViewModel, Activity, and Fragment:

ViewModel

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Activity

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Fragment

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Why does it not work?

The issue here lies in how the Fragment initializes its ViewModel. By deploying viewModel = ViewModelProvider(this).get(MyMusicViewModel::class.java), you're creating a separate instance of the MyMusicViewModel within the Fragment rather than using the one managed by the Activity. Therefore, the observer set in the Activity cannot respond to changes in the Fragment's ViewModel.

The Solution

To ensure that both your Activity and Fragment are using the same instance of MyMusicViewModel, you should modify your Fragment code. Instead of creating its own instance, the Fragment should refer to the Activity's ViewModel. You can achieve this by using the activityViewModels delegate as shown below:

Updated Fragment Code

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Key Changes

Use private val viewModel: MyMusicViewModel by activityViewModels() instead of ViewModelProvider(this).get(MyMusicViewModel::class.java). This ensures that both the Activity and Fragment are observing the same instance.

Conclusion

By having your Fragment use the same instance of ViewModel as your Activity, you enable proper observation of MutableLiveData changes. This adjustment not only resolves the problem but also aligns your architecture with Android's best practices. Keep exploring and experimenting with these concepts to enhance your Android development skills! If you have any questions, feel free to reach out in the comments below.