Inject ViewModels

Koject allows you to easily inject ViewModels into your Android application.

Setup for ViewModels

Add the appropriate dependencies for the injection target:

dependencies {
    // Inject ViewModel into Activity
    implementation("com.moriatsushi.koject:koject-android-activity:1.3.0")
    // Inject ViewModel into Fragment
    implementation("com.moriatsushi.koject:koject-android-fragment:1.3.0")
    // ViewModelFactory only
    implementation("com.moriatsushi.koject:koject-android-viewmodel:1.3.0")
}

Please also refer to the Setup document.

Using ViewModels

To define a ViewModel, specify the @ViewModelComponent and @Provides annotations. You can use constructor injection as with other types:

@Provides
@ViewModelComponent
class TopViewModel(
    private val userRepository: UserRepository,
    private val contentRepository: ContentRepository,
): ViewModel() {
    /* ... */
}

When using ViewModels, use the ComponentActivity.lazyViewModels() function:

class TopActivity : ComponentActivity() {
    private val viewModel: TopViewModel by lazyViewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        /* ... */
    }
}

For fragments, use the Fragment.lazyViewModels() function:

class TopFragment : Fragment() {
    private val viewModel: TopViewModel by lazyViewModels()

    override fun onCreateView(
        inflater: LayoutInflater,
        container: ViewGroup?,
        savedInstanceState: Bundle?,
    ): View? {
        /* ... */
    }
}

LINK

Refer to the documentation to inject ViewModels in Jetpack Compose.

MIGRATION (VERSION 1.3.0)

As of version v1.3.0, injectViewModels() has been renamed to lazyViewModels():

// Until v1.1.0
private val viewModel: TopViewModel by injectViewModels()

// Since v1.3.0
private val viewModel: TopViewModel by lazyViewModels()

Working with SavedStateHandle

SavedStateHandle is used to save ViewModel state. Koject allows you to inject SavedStateHandle out of the box.

@Provides
@ViewModelComponent
class SavedStateViewModel(
    private val savedStateHandle: SavedStateHandle
) : ViewModel() {
    /* ... */
}

class TopActivity : ComponentActivity() {
    private val viewModel: SavedStateViewModel by lazyViewModels()

    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        /* ... */
    }
}

Inject ViewModel's CoroutineScope

Types with ViewModelComponent annotations can only be injected into ViewModel and can inject ViewModel's CoroutineScope. The @ViewModelCoroutineScope qualifier is required to use the CoroutineScope.

@Provides
@ViewModelComponent
class ViewModelHelper(
    @ViewModelCoroutineScope
    val scope: CoroutineScope // same as ViewModel.viewModelScope
) {
    /* ... */
}

@Provides
@ViewModelComponent
class SomeViewModel(
    val helper: ViewModelHelper
): ViewModel() {
    /* ... */
}

LINK

Check the Android components documentation for all available components for Android.