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Learn how to create distinct ViewModels for each instance of a fragment in your Android app, ensuring they operate independently with custom fetchers.
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How to Create Different ViewModels for a Common Fragment in Android

In the world of Android development, managing the lifecycle and data of UI components can often be tricky, especially when you have multiple fragments that share similar layouts and functionalities. This is particularly challenging when each fragment requires a unique parameter for data fetching, such as the one described in this scenario.

Imagine having three fragments that look almost identical but need to operate with different data sources or parameters—let's call this parameter fetcher. The primary question here is: How do you ensure that each fragment has its own instance of a ViewModel while also passing the necessary fetcher parameter?

Understanding the Problem

When working with Kotlin and Android's architecture components, it’s common to retrieve a ViewModel for a fragment using:

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

However, this method will lead to all three fragments sharing the same instance of MyFragmentViewModel. Such a setup is problematic because each fragment should ideally manage its own data independently.

To solve this issue, we can utilize a custom ViewModelProvider.Factory. This factory pattern allows us to pass arguments—like our specific fetcher—to the ViewModel while creating a new instance for each fragment.

Step-by-Step Solution

1. Create a Custom ViewModel Factory

First, we need to subclass ViewModelProvider.Factory to create a custom factory. This factory will handle the instantiation of our MyFragmentViewModel with a specific fetcher.

Here’s how the factory implementation looks:

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

2. Use the Custom Factory in Your Fragment

Next, we need to modify the way we retrieve our ViewModel in the fragment. By providing our custom factory to the viewModels delegate, we can ensure that each fragment gets its unique instance of MyFragmentViewModel.

Here’s the updated code snippet:

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

3. Simplified Integration with Navigation

If you are using Android's Navigation component, you might want to streamline the parameter passing process. You can remove the fetcher argument from the fragment's constructor and leverage the SafeArgs plugin to pass an enum value or identifier that resolves to your different fetchers.

Conclusion

By employing a custom ViewModelProvider.Factory, you can create distinct ViewModels for each instance of a fragment, ensuring that they operate with their respective fetcher parameters. This approach not only adheres to good architectural practices but also maintains the independence of your fragment's data handling.

By following the steps outlined above, you can effectively create a scalable and maintainable architecture in your Android app.

Remember, structured and independent data management in your fragments is crucial for developing robust applications!