Kotlin无法创建ViewModel的实例 [英] Kotlin cannot create an instance of ViewModel
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问题描述
我的ViewModel遇到以下错误:
I've been getting the following error against my ViewModel:
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cryptpass_kt/com.example.cryptpass_kt.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.example.cryptpass_kt.EntryViewModel
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2853)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2928)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6703)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
Caused by: java.lang.RuntimeException: Cannot create an instance of class com.example.cryptpass_kt.EntryViewModel
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:238)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:164)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:130)
at com.example.cryptpass_kt.MainActivity.onCreate(MainActivity.kt:40)
at android.app.Activity.performCreate(Activity.java:6980)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2806)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2928)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6703)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
Caused by: java.lang.reflect.InvocationTargetException
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:334)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:230)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:164)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:130)
at com.example.cryptpass_kt.MainActivity.onCreate(MainActivity.kt:40)
at android.app.Activity.performCreate(Activity.java:6980)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2806)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2928)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6703)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property allEntries has not been initialized
at com.example.cryptpass_kt.EntryRepository.getAllEntries(EntryRepository.kt:9)
at com.example.cryptpass_kt.EntryViewModel.<init>(EntryViewModel.kt:11)
at java.lang.reflect.Constructor.newInstance0(Native Method)
at java.lang.reflect.Constructor.newInstance(Constructor.java:334)
at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:230)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:164)
at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:130)
at com.example.cryptpass_kt.MainActivity.onCreate(MainActivity.kt:40)
at android.app.Activity.performCreate(Activity.java:6980)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2806)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2928)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1609)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6703)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:769)
错误指向我的应用中的3个位置.第一个是我的 MainActivity.kt 类的 onCreate()方法中的 viewModel 对象的初始化:
The error points to 3 locations in my app. The first one being the initiation of the viewModel object in my MainActivity.kt class' onCreate() method:
override fun onCreate(savedInstanceState: Bundle?) {
...
viewModel = ViewModelProviders.of(this).get(EntryViewModel::class.java)
viewModel.allEntries.observe(this, Observer { entries -> adapter.submitList(entries) })
...
}
第二个点是我的存储库类中的 LiveData 对象:
The 2ndpoint is the LiveData object in my repository class:
class EntryRepository(application: Application) {
private val entryDAO: EntryDAO
lateinit var allEntries: LiveData<List<Entry>>
...
}
第三个要点是 ViewModel 内的存储库对象:
And the 3rd point is the repository object inside the ViewModel:
class EntryViewModel(application: Application) : AndroidViewModel(application) {
private val repository: EntryRepository = EntryRepository(application)
val allEntries: LiveData<List<Entry>>
init {allEntries = repository.allEntries }
fun insert(entry: Entry) {repository.insert(entry)}
fun update(entry: Entry) {repository.update(entry)}
fun delete(entry: Entry) {repository.update(entry)}
fun deleteAll() {repository.deleteAllEntries()}
}
我第一次遇到此错误时，在S/O上被告知，这是由于我的gradle文件中有一些与AnroidX不兼容的实现.解决此问题后，问题仍然存在.
The first time I had this error, I was told on S/O that it was due the fact that I had some implementations in my gradle file that were not AnroidX compatible. After fixing that, the problem still exists.
推荐答案
Caused by: kotlin.UninitializedPropertyAccessException: lateinit property allEntries has not been initialized
在 EntryViewModel 中，您具有以下一行:
In EntryViewModel, you have this line:
init {allEntries = repository.allEntries }
您正在引用 EntryRepository 的 allEntries 属性.定义为 lateinit :
You are referencing the allEntries property of the EntryRepository. That is defined as lateinit:
lateinit var allEntries: LiveData<List<Entry>>
错误告诉您在尝试引用 allEntries 之前尚未为其分配值.如果要在可见的(非 private )属性上使用 lateinit ，则需要确保在为其分配值之前，其他任何对象都可以尝试使用该属性属性.
The error is telling you that you have not assigned a value to allEntries before trying to reference it. If you are going to use lateinit on a visible (non-private) property, you need to ensure that you assign a value to it before any other object can try using that property.
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