Dagger-Hilt：@ViewModelInject 沒有注入 MyViewModel 並崩潰？

Question

在探索 Dagger-Hilt 的 ViewModelInject 時，我遵循https://developer.android.com/training/dependency-injection/hilt-jetpack#viewmodels中的示例

我嘗試將 ViewModel 注入到我的活動中，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<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"
}

它崩潰抱怨

     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)

我嘗試使用視圖 model 工廠（非注入方法）手動創建 ViewModel，它工作正常。

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"
}

我在使用@ViewModelInject時做錯了嗎？

Answer 1

顯然我錯過了添加一個 kapt，即kapt 'androidx.hilt:hilt-compiler:1.0.0-alpha01'

我的build.gradle中的依賴項列表如下

    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'

為了完整起見，插件如下

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

Answer 2

@ViewModelInject在較新的hilt版本中已棄用

https://developer.android.com/reference/androidx/hilt/lifecycle/ViewModelInject

使用HiltViewModel

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

}

Answer 3

嘗試通過在路徑中查找（⇧⌘F 或 Ctrl+Shift+F）搜索 ViewModel 生成的 java 文件，如下所示。

如果沒有自動生成的 java 文件。 這意味着您忘記將此依賴項添加到模塊的 gradle 文件中，該文件會為每個@HiltViewModel注釋生成必要的 java 文件。

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

Answer 4

我想補充一點，如果您在一個多模塊項目中，則必須在:app模塊上安裝kapt 'androidx.hilt:hilt-compiler:1.0.0-alpha01'才能使其正常工作。

Answer 5

對我來說，所有依賴項都完美放置，但錯過了繼承 ViewModel class (androidx.lifecycle.ViewModel)

視圖模型（）

class MainViewModel @ViewModelInject constructor(): ViewModel() 

Answer 6

確保您的app/build.gradle中有以下依賴項：

    // ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel-ktx:2.3.0"
    implementation "androidx.lifecycle:lifecycle-extensions:2.2.0"

    // Hilt
    implementation 'com.google.dagger:hilt-android:2.33-beta'
    kapt 'com.google.dagger:hilt-compiler:2.33-beta'

    // Hilt ViewModel
    implementation "androidx.hilt:hilt-lifecycle-viewmodel:1.0.0-alpha03"
    kapt "androidx.hilt:hilt-compiler:1.0.0-beta01"