Automatic resource cleanup in Jetpack ViewModels using AutoCloseable

When building Android applications with Jetpack ViewModels, proper resource management is crucial to prevent memory leaks and ensure efficient cleanup of services. In this post, we’ll explore an elegant pattern that leverages Kotlin’s AutoCloseable interface to clean up resources when a ViewModel is destroyed automatically.

The Problem

Traditionally, when a ViewModel needs to clean up resources, we override the onCleared() method:

class MyViewModel(private val itemsService: ItemsService) : ViewModel() {

    override fun onCleared() {
        super.onCleared()
        itemsService.cleanup()
    }
}

While this works, it requires boilerplate code for each service that needs cleanup.

AutoCloseable Pattern

Android’s ViewModel class supports automatic resource cleanup through the AutoCloseable interface. When a ViewModel is cleared, any services that implement AutoCloseable and are passed to the ViewModel constructor will automatically have their close() method invoked.

Implementing AutoCloseable Services

First, make your service implement AutoCloseable:

interface ItemsService : AutoCloseable {
    val items: Flow<List<Item>>
    suspend fun getItems(): List<Item>
    // ... other methods
}

Then implement the close() method:

class RealItemsService : ItemsService {
    private val scope = CoroutineScope(SupervisorJob() + Dispatchers.Default)

    [....]

    override fun close() {
        scope.cancel()
        println("ItemsService closed - resources cleaned up")
    }
}

Passing AutoCloseable Services to a ViewModel

Here’s the key: you can directly pass all your AutoCloseable services to the ViewModel constructor, and let the framework handle cleanup automatically.

class HomeViewModel(
    private val itemsService: ItemsService,
    private val customersService: CustomersService,
    private val invoiceService: InvoiceService
) : ViewModel(
    itemsService,
    customersService,
    invoiceService
) {

    [....]    
}

When HomeViewModel is cleared, the Android framework automatically calls close() on each of these services — no need to override onCleared() or introduce a custom BaseViewModel.

Conclusion

The AutoCloseable pattern in ViewModels provides an elegant solution for automatic resource management. By implementing AutoCloseable on your services and passing them to the ViewModel constructor, you ensure proper cleanup without writing repetitive boilerplate code. This approach leads to cleaner, more maintainable code while preventing memory leaks and ensuring resources are released appropriately.

Happy coding!

Comments

[Nikola Despotoski]

Viewmodels allow you to register any closable object without overriding clear function.

class MainViewModel @Inject constructor(myService : MyService...): ViewModel() {

    init { 
      addClosable(myService)
   }

}

Assuming the service class implements Closable or AutoClosable