无法创建视图模型类的实例

Question

我正在使用 MVVM 架构，但我不明白为什么会出现此错误？我的其他类具有相同的结构，并且它们运行良好。下面我分享了我的片段类和 ViewModel 类的代码以及错误

错误

E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.beyond.sellandtrack, PID: 5380
java.lang.RuntimeException: Cannot create an instance of class com.beyond.sellandtrack.screens.dashboard.DashboardViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:275)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150)
at com.beyond.sellandtrack.screens.dashboard.DashboardFragment.onCreateView(DashboardFragment.kt:33)
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698)
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320)
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187)
at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224)
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997)
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953)
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849)
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413)
at android.os.Handler.handleCallback(Handler.java:809)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:166)
at android.app.ActivityThread.main(ActivityThread.java:7555)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:963)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:334)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267)
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106) 
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185) 
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150) 
at com.beyond.sellandtrack.screens.dashboard.DashboardFragment.onCreateView(DashboardFragment.kt:33) 
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698) 
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320) 
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187) 
at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224) 
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997) 
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953) 
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849) 
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413) 
at android.os.Handler.handleCallback(Handler.java:809) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:166) 
at android.app.ActivityThread.main(ActivityThread.java:7555) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:963) 
Caused by: kotlin.KotlinNullPointerException
at com.beyond.sellandtrack.screens.dashboard.DashboardViewModel.<init>(DashboardViewModel.kt:20)
at java.lang.reflect.Constructor.newInstance0(Native Method) 
at java.lang.reflect.Constructor.newInstance(Constructor.java:334) 
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:267) 
at androidx.lifecycle.SavedStateViewModelFactory.create(SavedStateViewModelFactory.java:106) 
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:185) 
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:150) 
at com.beyond.sellandtrack.screens.dashboard.DashboardFragment.onCreateView(DashboardFragment.kt:33) 
at androidx.fragment.app.Fragment.performCreateView(Fragment.java:2698) 
at androidx.fragment.app.FragmentStateManager.createView(FragmentStateManager.java:320) 
at androidx.fragment.app.FragmentManager.moveToState(FragmentManager.java:1187) 
at androidx.fragment.app.FragmentManager.addAddedFragments(FragmentManager.java:2224) 
at androidx.fragment.app.FragmentManager.executeOpsTogether(FragmentManager.java:1997) 
at androidx.fragment.app.FragmentManager.removeRedundantOperationsAndExecute(FragmentManager.java:1953) 
at androidx.fragment.app.FragmentManager.execPendingActions(FragmentManager.java:1849) 
at androidx.fragment.app.FragmentManager$4.run(FragmentManager.java:413) 
at android.os.Handler.handleCallback(Handler.java:809) 
at android.os.Handler.dispatchMessage(Handler.java:102) 
at android.os.Looper.loop(Looper.java:166) 
at android.app.ActivityThread.main(ActivityThread.java:7555) 
at java.lang.reflect.Method.invoke(Native Method) 
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:469) 
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:963) 

I/进程：发送信号。PID： 5380 SIG： 9 与目标虚拟机断开连接，地址："本地主机：8600"，传输："套接字">

片段类

class DashboardFragment : Fragment() {
private lateinit var dashboardViewModel: DashboardViewModel
override fun onCreateView(
inflater: LayoutInflater, container: ViewGroup?,
savedInstanceState: Bundle?
): View? {
// Inflate the layout for this fragment
val binding = DataBindingUtil.inflate<FragmentDashboardBinding>(
inflater,R.layout.fragment_dashboard,container,false
)
dashboardViewModel= ViewModelProvider(this).get(DashboardViewModel::class.java)

视图模型类

class DashboardViewModel(application: Application) : AndroidViewModel(application) {
lateinit var user: User
private var auth : FirebaseAuth = FirebaseAuth.getInstance()
private var repository: Repository = Repository()
init {
user =  repository.getUserData()!!
}

Answer 1

您需要检查 getUserData 是否不为空。 在初始化块中

init {
user =  repository.getUserData()!! //you are forcefully marking this as non null
}

检查getUserData((是否在此处返回 null。这很可能是空的，这就是它失败的原因

Answer 2

我认为您应该尝试Koin注入并创建ViewModel的实例。 它易于使用，语法简短。 https://insert-koin.io/。

// Injected by constructor
class MyViewModel(val repo : MyRepository) : ViewModel()
// declared ViewModel using the viewModel keyword
val myModule : Module = module {
viewModel { MyViewModel(get()) } 
single { MyRepository() }
}
// Just get it
class MyActivity() : AppCompatActivity() {
// lazy inject MyViewModel
val myViewModel : MyViewModel by viewModel()
}

Answer 3

我认为你的 DashboardViewModel 类应该从 ViewModel(( 而不是 AndroidViewModel(( 扩展

实现"androidx.lifecycle：lifecycle-viewmodel-ktx：2.2.0">

import androidx.lifecycle.ViewModel
class DashboardViewModel : ViewModel()