SavedStateHandle Integration

eungabi 0.4.0 introduces a powerful SavedState mechanism, enabling seamless state preservation and data transfer in conjunction with ViewModels. With this new feature, each ViewModel can now access a SavedStateHandle object, a key-value map that allows you to store and retrieve data directly within the ViewModel. Crucially, the data within the ViewModelSavedState persists even through process termination and configuration changes, ensuring that your ViewModel's state remains intact.

Using SavedStateHandle in EunGabi

EunGabi provides several convenient ways to utilize SavedStateHandle for managing state across navigation events. Here are the primary methods:

1. Accessing SavedStateHandle via EunGabiController

You can access the SavedStateHandle of a specific EunGabiEntry by leveraging the EunGabiController.backStack. This allows you to retrieve the SavedStateHandle from any entry within the navigation back stack.

val controller = rememberEunGabiController()
val backStack by controller.backStack. collectAsState()
val handle = backStack.last().savedStateHandle 
val viewModel = viewModel { ViewModel(handle) }

Explanation:

• rememberEunGabiController(): Retrieves the current EunGabiController instance.
• controller.backStack.collectAsState(): Collects the current state of the back stack as a State object.
• backStack.last().savedStateHandle: Accesses the SavedStateHandle of the most recent entry in the back stack.
• viewModel { ViewModel(handle) }: Creates a ViewModel instance with the SavedStateHandle.

2. Accessing SavedStateHandle within NavGraphBuilder.composable()

Within the content block of NavGraphBuilder.composable(), you can directly access the SavedStateHandle of the current EunGabiEntry.

NavHost(...) { 
    composable(...) { entry -> 
        val handle = entry.savedStateHandle
        val viewModel = viewModel { ViewModel(handle) } 
    }
}

Explanation:

• composable(...) { entry -> ... }: The composable function provides the current EunGabiEntry as a parameter.
• entry.savedStateHandle: Directly accesses the SavedStateHandle associated with the current entry.
• viewModel { ViewModel(handle) }: Creates a ViewModel instance with the SavedStateHandle.

3. Using Parameter Default Values with eunGabiViewModel()

For a more streamlined approach, you can use the eunGabiViewModel(...) function to inject the SavedStateHandle directly into your composable function's parameters.

eunGabiViewModel automatically recognizes the currently active EunGabiEntry and provides the corresponding SavedStateHandle.

@Composable 
fun EunGabiScreen( 
    viewModel: EunGabiViewModel = eunGabiViewModel { handle -> EunGabiViewModel(handle) }
) { ... }

Explanation:

• eunGabiViewModel { handle -> EunGabiViewModel(handle) }: This function automatically provides the correct SavedStateHandle to the lambda, which you can then use to create your EunGabiViewModel.
• EunGabiViewModel(handle): Creates a EunGabiViewModel instance with the SavedStateHandle.

Hilt Integration

When using Hilt in your Android target, you can seamlessly inject the appropriate SavedStateHandle using hiltViewModel().

@Composable  
fun HiltView(viewModel: HiltViewModel = hiltViewModel()) {  
    val state by viewModel.state.collectAsState()  
    Text(text = state, modifier = Modifier.testTag("state"))  
}

Explanation:

• hiltViewModel(): This Hilt function automatically provides the correct SavedStateHandle to your HiltViewModel.
• viewModel.state.collectAsState(): Collects the current state of the ViewModel.

Tip

For a practical example of Hilt integration, refer to the EunGabiHiltTest.kt file in the EunGabi repository.

Koin Integration

Similarly, when using Koin in your KMP project, you can easily inject the SavedStateHandle using koinViewModel(). Koin, like Hilt, internally recognizes the current entry and provides the correct SavedStateHandle.

@Composable  
fun KoinView(  
    viewModel: KoinViewModel = koinViewModel()  
) {  
    val state by viewModel.state.collectAsState()  
    Text(text = state, modifier = Modifier.testTag("state"))  
}

Explanation:

• koinViewModel(): This Koin function automatically provides the correct SavedStateHandle to your KoinViewModel.
• viewModel.state.collectAsState(): Collects the current state of the ViewModel.

Tip

For a practical example of Koin integration, refer to the KoinViewModelTest.kt file in the EunGabi repository.