Creating SharedViewModel in Android

Shared ViewModel

Sharing data between different components in an Android app is a common requirement. One effective way to achieve this is by using ViewModels. In this guide, we’ll explore various methods to create a SharedViewModel in Android.

1. activityViewModels()

The activityViewModels() delegate is a powerful tool for sharing a ViewModel across an entire activity. This is suitable for managing global app data such as user preferences or authentication state. Here's an example:

// Access shared ViewModel within composables
val sharedViewModel: MySharedViewModel by activityViewModels()
// Update and display data
Text(text = sharedViewModel.updatedEmail)
Button(onClick = { sharedViewModel.updateEmail("email@example.com") }) {
  Text("Email Update")
}kotl

2. navGraphViewModels()

When dealing with a navigation graph, use navGraphViewModels() to share a ViewModel across composables belonging to a specific navigation flow. This is useful for managing data related to a particular navigation path, like product details within a product list. Example:

// Access shared ViewModel within a navigation graph
val sharedViewModel: MySharedViewModel by navGraphViewModels(R.id.mobile_navigation)
// Display product information in composables
Text(text = sharedViewModel.name)
Image(sharedViewModel.image)

3. rememberViewModel()

Creating a ViewModel instance specific to a composable subtree rememberViewModel() is a handy option. This is useful when dealing with data relevant only to a particular part of the UI, like shopping cart items within a cart screen. Example:

// Create and access a ViewModel specific to a composable subtree
val sharedViewModel: MySharedViewModel = rememberViewModel()
// Use data and functions within composables
SharedItems(sharedViewModel.items)
CheckoutButton(onClick = { sharedViewModel.checkout() })

4. Dependency Injection (DI) Libraries

Consider using Dependency Injection (DI) libraries such as Hilt or Dagger for a more organized and testable approach. These libraries facilitate the injection of shared ViewModels into composables. Here’s a high-level overview:

@HiltViewModel class MySharedViewModel @Inject constructor() : ViewModel() 
{  // ViewModel code }

By adopting one or a combination of these approaches, you can efficiently manage shared data and functionality across different parts of your Android app. Choose the method that aligns with your app’s architecture and complexity.