Dagger-Hilt：@ViewModelInject没有注入MyViewModel并崩溃吗？

Question

在探索Dagger-Hilt的ViewModelInject时，我遵循了https://developer.android.com/training/dependency-injection/hilt-jetpack#viewmodels我尝试将ViewModel注入到我的活动中，如下所示

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 { 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("DefaultKey")

    val showTextDataNotifier: LiveData
        get() = showTextLiveData

    fun fetchValue() {
        showTextLiveData.value = repository.getMessage()
    }
}


@Singleton
class Repository @Inject constructor() {
    fun getMessage() = "From Repository"
}

It崩溃抱怨

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)

我尝试使用视图模型工厂(非注入方法)手动创建ViewModel，它工作得很好。

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 { 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  create(key: String, modelClass: Class, 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("DefaultKey")

    val showTextDataNotifier: LiveData
        get() = showTextLiveData

    fun fetchValue() {
        showTextLiveData.value = repository.getMessage()
    }
}

@Singleton
class Repository @Inject constructor() {
    fun getMessage() = "From Repository"
}

我在使用的时候做错了什么吗？@ViewModelInject

Answer 1

显然，我错过了添加一个kapt，这是kapt 'androidx.hilt:hilt-compiler:1.0.0-alpha01'中的依赖项列表build.gradle如下所示

implementation 'androidx.fragment:fragment-ktx:1.2.5'
    implementation "androidx.lifecycle:lifecycle-viewmodel:2.2.0"
    implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"
    implementation "androidx.hilt:hilt-lifecycle-viewmodel:1.0.0-alpha01"
    implementation 'com.google.dagger:hilt-android:2.28-alpha'
    kapt 'androidx.hilt:hilt-compiler:1.0.0-alpha01'
    kapt 'com.google.dagger:hilt-android-compiler:2.28-alpha'

为了完整起见，下面是插件

apply plugin: 'dagger.hilt.android.plugin'
apply plugin: 'kotlin-kapt'

Answer 2

@ViewModelInject在较新的版本中已被弃用。hilt版本https://developer.android.com/reference/androidx/hilt/lifecycle/ViewModelInject

使用HiltViewModel

@HiltViewModel
class TasksViewModel @Inject constructor(
    val taskRepository: TaskRepository
) : ViewModel() {

}

Answer 3

尝试通过Find in Path (⇧⌘F或Ctrl+Shift+F)搜索ViewModel生成的java文件，如下所示。

如果没有自动生成的java文件。这意味着您忘记将此依赖项添加到模块的gradle文件中，该文件为@ViewModelInject注释。

kapt "androidx.hilt:hilt-compiler:$version"