In exploring the ViewModelInject of Dagger-Hilt, I follow the example in https://developer.android.com/training/dependency-injection/hilt-jetpack#viewmodels
I try to inject the ViewModel into my activity as follow
import android.app.Application
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.activity.viewModels
import androidx.hilt.Assisted
import androidx.hilt.lifecycle.ViewModelInject
import androidx.lifecycle.*
import androidx.savedstate.SavedStateRegistryOwner
import dagger.hilt.android.AndroidEntryPoint
import dagger.hilt.android.HiltAndroidApp
import kotlinx.android.synthetic.main.activity_main.*
import javax.inject.Inject
import javax.inject.Singleton
@HiltAndroidApp
class MainApplication: Application()
@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
private val viewModel: MyViewModel by viewModels()
private val textDataObserver =
Observer<String> { data -> text_view.text = data }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModel.showTextDataNotifier.observe(this, textDataObserver)
btn_fetch.setOnClickListener { viewModel.fetchValue() }
}
}
class MyViewModel @ViewModelInject constructor(
@Assisted val savedStateHandle: SavedStateHandle,
val repository: Repository
) :
ViewModel(), LifecycleObserver {
private val showTextLiveData
= savedStateHandle.getLiveData<String>("DefaultKey")
val showTextDataNotifier: LiveData<String>
get() = showTextLiveData
fun fetchValue() {
showTextLiveData.value = repository.getMessage()
}
}
@Singleton
class Repository @Inject constructor() {
fun getMessage() = "From Repository"
}
It crash complaining
Caused by: java.lang.RuntimeException: Cannot create an instance of class com.elyeproj.simplehilt.MyViewModel
at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:221)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:278)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.hilt.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:69)
I try manually creating the ViewModel using the view model factory (the non-injection approach), it works fine.
import android.app.Application
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import androidx.activity.viewModels
import androidx.hilt.Assisted
import androidx.hilt.lifecycle.ViewModelInject
import androidx.lifecycle.*
import androidx.savedstate.SavedStateRegistryOwner
import dagger.hilt.android.AndroidEntryPoint
import dagger.hilt.android.HiltAndroidApp
import kotlinx.android.synthetic.main.activity_main.*
import javax.inject.Inject
import javax.inject.Singleton
@HiltAndroidApp
class MainApplication: Application()
@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
private val viewModel: MyViewModel by viewModels{
MyViewModelFactory(this, Repository(), intent.extras)
}
private val textDataObserver =
Observer<String> { data -> text_view.text = data }
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_main)
viewModel.showTextDataNotifier.observe(this, textDataObserver)
btn_fetch.setOnClickListener { viewModel.fetchValue() }
}
}
class MyViewModelFactory(
owner: SavedStateRegistryOwner,
private val repository: Repository,
defaultArgs: Bundle? = null
) : AbstractSavedStateViewModelFactory(owner, defaultArgs) {
override fun <T : ViewModel> create(key: String, modelClass: Class<T>, handle: SavedStateHandle
): T {
return MyViewModel(
handle,
repository
) as T
}
}
class MyViewModel @ViewModelInject constructor(
@Assisted val savedStateHandle: SavedStateHandle,
val repository: Repository
) :
ViewModel(), LifecycleObserver {
private val showTextLiveData
= savedStateHandle.getLiveData<String>("DefaultKey")
val showTextDataNotifier: LiveData<String>
get() = showTextLiveData
fun fetchValue() {
showTextLiveData.value = repository.getMessage()
}
}
@Singleton
class Repository @Inject constructor() {
fun getMessage() = "From Repository"
}
Did I do anything wrong in the use of @ViewModelInject
?
Inject ViewModel objects with Hilt Provide a ViewModel by annotating it with @HiltViewModel and using the @Inject annotation in the ViewModel object's constructor. Note: To use Dagger's assisted injection with ViewModels, see the following Github issue.
Dagger and Hilt code can coexist in the same codebase. However, in most cases, it's best to use Hilt to manage all your use of Dagger on Android.
There are three steps to setting up and using a ViewModel: Separate out your data from your UI controller by creating a class that extends ViewModel. Set up communications between your ViewModel and your UI controller. Use your ViewModel in your UI controller.
Hilt provides a standard way to incorporate Dagger dependency injection into an Android application. The goals of Hilt are: To simplify Dagger-related infrastructure for Android apps. To create a standard set of components and scopes to ease setup, readability/understanding, and code sharing between apps.
@ViewModelInject
is deprecated in the newer hilt
version
https://developer.android.com/reference/androidx/hilt/lifecycle/ViewModelInject
Use HiltViewModel
@HiltViewModel
class TasksViewModel @Inject constructor(
val taskRepository: TaskRepository
) : ViewModel() {
}
I'd like to add that If you are on a multi-module project, you have to have kapt 'androidx.hilt:hilt-compiler:1.0.0-alpha01'
on the :app
module as well for it to work.
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