无法创建 class 视图模型的实例 - Kotlin

Question

我目前正在做一个项目，用 Dagger-Hilt 练习依赖注入，但是我无法让我的 ViewModel 实例化，我已经看过关于同一主题的其他一些问题，大多数点Gradle 的问题，但这并没有为我解决问题，Stacktrace 中的所有错误都来自内部类，除了在 MainActivity

中涉及我的 ViewModel 的 2 行

这是堆栈跟踪：

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.practiceproject, PID: 9873
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.practiceproject/com.example.practiceproject.ui.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.example.practiceproject.ui.viewmodel.DogViewModel
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3270)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409)
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83)
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016)
    at android.os.Handler.dispatchMessage(Handler.java:107)
    at android.os.Looper.loop(Looper.java:214)
    at android.app.ActivityThread.main(ActivityThread.java:7356)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)
 Caused by: java.lang.RuntimeException: Cannot create an instance of class com.example.practiceproject.ui.viewmodel.DogViewModel
    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:112)
    at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:146)
    at dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:111)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187)
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
    at androidx.lifecycle.ViewModelLazy.getValue(ViewModelProvider.kt:54)
    at androidx.lifecycle.ViewModelLazy.getValue(ViewModelProvider.kt:41)
    at com.example.practiceproject.ui.MainActivity.getDogViewModel(MainActivity.kt:15)
    at com.example.practiceproject.ui.MainActivity.onCreate(MainActivity.kt:22)
    at android.app.Activity.performCreate(Activity.java:7802)
    at android.app.Activity.performCreate(Activity.java:7791)
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930) 
 Caused by: java.lang.InstantiationException: java.lang.Class<com.example.practiceproject.ui.viewmodel.DogViewModel> has no zero argument constructor
    at java.lang.Class.newInstance(Native Method)
    at androidx.lifecycle.ViewModelProvider$NewInstanceFactory.create(ViewModelProvider.java:219)
    at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:278) 
    at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:112) 
    at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:146) 
    at dagger.hilt.android.internal.lifecycle.HiltViewModelFactory.create(HiltViewModelFactory.java:111) 
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:187) 
    at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150) 
    at androidx.lifecycle.ViewModelLazy.getValue(ViewModelProvider.kt:54) 
    at androidx.lifecycle.ViewModelLazy.getValue(ViewModelProvider.kt:41) 
    at com.example.practiceproject.ui.MainActivity.getDogViewModel(MainActivity.kt:15) 
    at com.example.practiceproject.ui.MainActivity.onCreate(MainActivity.kt:22) 
    at android.app.Activity.performCreate(Activity.java:7802) 
    at android.app.Activity.performCreate(Activity.java:7791) 
    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1299) 
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3245) 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3409) 
    at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:83) 
    at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135) 
    at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95) 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2016) 
    at android.os.Handler.dispatchMessage(Handler.java:107) 
    at android.os.Looper.loop(Looper.java:214) 
    at android.app.ActivityThread.main(ActivityThread.java:7356) 
    at java.lang.reflect.Method.invoke(Native Method) 
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:492) 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:930)

这是视图模型：

class DogViewModel @Inject constructor(
private val getDefaultImages: GetDefaultImages
) : ViewModel() {

val dogModel = MutableLiveData<DogModel>()
val isLoading = MutableLiveData<Boolean>()

fun onCreate() {
    viewModelScope.launch {
        isLoading.value = true
        val result = getDefaultImages()
        if(!result.isNullOrEmpty()) {
            dogModel.value = result[0]
            isLoading.value = false
        }
    }
}

这就是我要声明的地方：

@AndroidEntryPoint
class MainActivity : AppCompatActivity() {
private lateinit var binding: ActivityMainBinding

private val dogViewModel: DogViewModel by viewModels()

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    binding = ActivityMainBinding.inflate(layoutInflater)
    setContentView(binding.root)

    dogViewModel.onCreate()

    dogViewModel.dogModel.observe(this) {
        initRecyclerView(it)
    }
}

Answer 1

如果不在 DogViewModel 中使用 getDefaultImages 对象，您可以删除它，它会起作用。如果使用它，则需要使用 ViewModelProvider.Factory:

将 GetDefaultImages class 的实例传递给 DogViewModel

@Suppress("UNCHECKED_CAST")
private val factory: ViewModelProvider.Factory = object : ViewModelProvider.Factory {
    override fun <T : ViewModel> create(modelClass: Class<T>): T {
        return DogViewModel(GetDefaultImages()) as T
    }

}

private val dogViewModel: MyViewModel by viewModels { factory }

Answer 2

您应该在视图模型顶部添加 @HiltViewModel 注释。

无法创建 class 视图模型的实例 - Kotlin

Cannot create an instance of class view model - Kotlin

android

viewmodel

kotlin

android-viewmodel