How to dynamically set the bundle from AbstractSavedStateViewModelFactory

Question

My ViewModelFactory:

class ViewModelFactory @Inject constructor(
    private val viewModelMap: MutableMap<Class<out ViewModel>, ViewModelAssistedFactory<out ViewModel>>,
    owner: SavedStateRegistryOwner,
    defaultArgs: Bundle?
) : AbstractSavedStateViewModelFactory(owner, defaultArgs) {

    @Throws(IllegalStateException::class)
    @Suppress("UNCHECKED_CAST")
    override fun <T : ViewModel?> create(key: String, modelClass: Class<T>, handle: SavedStateHandle): T {
        return viewModelMap[modelClass]?.create(handle) as? T ?: throw IllegalStateException("Unknown ViewModel class")
    }
}

Activity:

@Inject
lateinit var viewModelFactory: ViewModelFactory
protected val viewModel: ViewModel by lazy { ViewModelProvider(this, viewModelFactory).get(getViewModelClass()) }

ViewModel:

@AssistedInject.Factory
interface Factory : ViewModelAssistedFactory<SplashViewModel>

And I was wondering how can I provide the defaultArgs dynamically instead of:

ActivityModule

@Module
    companion object {
        @JvmStatic
        @Nullable
        @Provides
        fun provideDefaultArgs(): Bundle? {
            return null
        }
    }

The idea is to have the possibility to send a parameter to the ViewModel, let's say an ID for a DetailActivity. Normally I use an "init" method, but If I could use the StateHandle map would be even better. Something like this and this.

Makes sense? Is it possible?

This might sound crazy, but it sounds like you need to provide `ViewModelProvider.Factory` via AssistedInject. — EpicPandaForce, Jan 26 '20 at 17:33
Shouldn't we try to `AssistedInject` the `Bundle` like we do with the `ViewModelAssistedFactory`? — GuilhE, Jan 27 '20 at 10:37
Exactly. To get an instance of `AbstractSavedStateViewModelFactory` with the `Bundle` passed in through `AssistedInject`, you will end up creating the VMFactory through assisted injection. — EpicPandaForce, Jan 27 '20 at 11:29
can you please answer this https://stackoverflow.com/questions/60669372/retain-edittext-with-screen-rotation-using-databinding-library — NullByte08, Mar 13 '20 at 15:22

GuilhE · Accepted Answer · 2020-06-12T16:49:26.737

I came across 2 solutions:

Solution A:

Change our ViewModelFactory to:

class ViewModelFactory @Inject constructor(
    private val viewModelMap: MutableMap<Class<out ViewModel>, ViewModelAssistedFactory<out ViewModel>>
) {
    fun create(owner: SavedStateRegistryOwner, defaultArgs: Bundle? = null): AbstractSavedStateViewModelFactory {
        return object : AbstractSavedStateViewModelFactory(owner, defaultArgs) {
            @Suppress("UNCHECKED_CAST")
            override fun <T : ViewModel?> create(key: String, modelClass: Class<T>, handle: SavedStateHandle): T {
                return viewModelMap[modelClass]?.create(handle) as? T ?: throw IllegalStateException("Unknown ViewModel class")
            }
        }
    }
}

And finally:

@Inject
lateinit var viewModelFactory: ViewModelFactory
protected val viewModel: ViewModel by lazy { ViewModelProvider(this, viewModelFactory.create(this, args).get(getViewModelClass()) }

Also, we can simplify our ActivityModule to (example):

@AssistedModule
@Module(includes = [AssistedInject_SplashActivityModule::class])
abstract class SplashActivityModule{

    @Binds
    @IntoMap
    @ViewModelKey(SplashViewModel::class)
    abstract fun bindFactory(factory: SplashViewModel.Factory): ViewModelAssistedFactory<out ViewModel>
}

This post by Tomáš Mlynarič helped with this solution.

Solution B:

Create a Factory without injected dependencies:

class ViewModelFactoryAlt<out V : ViewModel>(
    private val viewModelFactory: ViewModelAssistedFactory<V>,
    owner: SavedStateRegistryOwner,
    defaultArgs: Bundle? = null
) : AbstractSavedStateViewModelFactory(owner, defaultArgs) {

    @Suppress("UNCHECKED_CAST")
    override fun <T : ViewModel> create(key: String, modelClass: Class<T>, handle: SavedStateHandle): T {
        return viewModelFactory.create(handle) as T
    }
}

Create our ViewModelAssitedFactory like:

class HelloWorldViewModelFactory @Inject constructor(
    private val dependencyA: DependencyA,
    ...
) : ViewModelAssistedFactory<HelloWorldViewModel> {
    override fun create(stateHandle: SavedStateHandle): HelloWorldViewModel {
        return HelloWorldViewModel(stateHandle, dependencyA, ...)
    }
}

And finally:

@Inject
lateinit var factory: HelloWorldViewModelFactory
private val viewModel: HelloWorldViewModel by viewModels { ViewModelFactoryAlt(factory, this, intent.extras) }

This post by Elye helped with this solution.

How to dynamically set the bundle from AbstractSavedStateViewModelFactory

1 Answers1