无法创建类ViewModel kotlin的实例 [英] Cannot create an instance of class ViewModel kotlin
问题描述
这是我的代码
class BookmarkViewModel(app: Application) : AndroidViewModel(app) {
private val dao = BookmarkDb.get(app).bookmarkDao()
companion object {
private const val PAGE_SIZE = PagingConstants.PERPAGE
/**
* If placeholders are enabled, PagedList will report the full size but some items might
* be null in onBind method (PagedListAdapter triggers a rebind when data is loaded).
* <p>
* If placeholders are disabled, onBind will never receive null but as more pages are
* loaded, the scrollbars will jitter as new pages are loaded. You should probably disable
* scrollbars if you disable placeholders.
*/
private const val ENABLE_PLACEHOLDERS = true
}
val allBookmarks = LivePagedListBuilder(dao.allBookmarkByDatetime(), PagedList.Config.Builder()
.setPageSize(PAGE_SIZE)
.setEnablePlaceholders(ENABLE_PLACEHOLDERS)
.build()).build()
fun insert(title: String, description: String, datetime: String) = ioThread {
dao.insert(Bookmark(id = 0, title = title, description = description, datetime = datetime))
}
fun remove(bookmark: Bookmark) = ioThread {
dao.delete(bookmark)
}
}
这是来自google示例. 在我想要之后:
This is from the google samples.. After I want to:
class BookmarkListFragment : FirstFragment() {
private var viewModel: BookmarkViewModel? = null
..
override fun onActivityCreated(savedInstanceState: Bundle?) {
super.onActivityCreated(savedInstanceState)
viewModel = ViewModelProviders.of(activity!!).get(BookmarkViewModel::class.java)
...
这是问题所在:
java.lang.RuntimeException:无法创建com.lacas.db.room.BookmarkViewModel类的实例
我可以在片段中使用它吗?
Can I use this in a fragment?
java.lang.RuntimeException:无法启动活动ComponentInfo {com.lacas.asd/com.lacas.asd.ui.activities.testtabs.TestTab2Activity}:java.lang.RuntimeException:无法创建com类的实例. lacas.asd.db.room.BookmarkViewModel 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2924) 在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) 在android.app.ActivityThread.-wrap14(ActivityThread.java) 在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1635) 在android.os.Handler.dispatchMessage(Handler.java:102) 在android.os.Looper.loop(Looper.java:154) 在android.app.ActivityThread.main(ActivityThread.java:6692) 在java.lang.reflect.Method.invoke(本机方法) 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:1468) 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) 原因:java.lang.RuntimeException:无法创建com.lacas.asd.db.room.BookmarkViewModel类的实例 在android.arch.lifecycle.ViewModelProvider $ AndroidViewModelFactory.create(ViewModelProvider.java:207) 在android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) 在android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity $ viewModel $ 2.invoke(TestTab2Activity.kt:34) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity $ viewModel $ 2.invoke(TestTab2Activity.kt:29) 在kotlin.UnsafeLazyImpl.getValue(Lazy.kt:154) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity.getViewModel(TestTab2Activity.kt) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity.onCreated(TestTab2Activity.kt:45) 在com.lacas.asd.base.BasePermissionsActivity.onCreate(BasePermissionsActivity.kt:34) 在android.app.Activity.performCreate(Activity.java:6912) 在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877) 在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) 在android.app.ActivityThread.-wrap14(ActivityThread.java) 在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1635) 在android.os.Handler.dispatchMessage(Handler.java:102) 在android.os.Looper.loop(Looper.java:154) 在android.app.ActivityThread.main(ActivityThread.java:6692) 在java.lang.reflect.Method.invoke(本机方法) 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:1468) 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) 造成原因:java.lang.reflect.InvocationTargetException 在java.lang.reflect.Constructor.newInstance0(本机方法) 在java.lang.reflect.Constructor.newInstance(Constructor.java:430) 在android.arch.lifecycle.ViewModelProvider $ AndroidViewModelFactory.create(ViewModelProvider.java:199) 在android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) 在android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity $ viewModel $ 2.invoke(TestTab2Activity.kt:34) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity $ viewModel $ 2.invoke(TestTab2Activity.kt:29) 在kotlin.UnsafeLazyImpl.getValue(Lazy.kt:154) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity.getViewModel(TestTab2Activity.kt) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity.onCreated(TestTab2Activity.kt:45) 在com.lacas.asd.base.BasePermissionsActivity.onCreate(BasePermissionsActivity.kt:34) 在android.app.Activity.performCreate(Activity.java:6912) 在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877) 在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) 在android.app.ActivityThread.-wrap14(ActivityThread.java) 在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1635) 在android.os.Handler.dispatchMessage(Handler.java:102) 在android.os.Looper.loop(Looper.java:154) 在android.app.ActivityThread.main(ActivityThread.java:6692) 在java.lang.reflect.Method.invoke(本机方法) 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:1468) 在com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) 由以下原因引起:java.lang.RuntimeException:找不到com.lacas.asd.db.room.BookmarkDb的实现. BookmarkDb_Impl不存在 在android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:93) 在android.arch.persistence.room.RoomDatabase $ Builder.build(RoomDatabase.java:630) 在com.lacas.asd.db.room.BookmarkDb $ Companion.get(BookmarkDb.kt:29) 在com.lacas.asd.db.room.BookmarkViewModel.(BookmarkViewModel.kt:14) 在java.lang.reflect.Constructor.newInstance0(本机方法) 在java.lang.reflect.Constructor.newInstance(Constructor.java:430) 在android.arch.lifecycle.ViewModelProvider $ AndroidViewModelFactory.create(ViewModelProvider.java:199) 在android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) 在android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity $ viewModel $ 2.invoke(TestTab2Activity.kt:34) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity $ viewModel $ 2.invoke(TestTab2Activity.kt:29) 在kotlin.UnsafeLazyImpl.getValue(Lazy.kt:154) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity.getViewModel(TestTab2Activity.kt) 在com.lacas.asd.ui.activities.testtabs.TestTab2Activity.onCreated(TestTab2Activity.kt:45) 在com.lacas.asd.base.BasePermissionsActivity.onCreate(BasePermissionsActivity.kt:34) 在android.app.Activity.performCreate(Activity.java:6912) 在android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) 在android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877) 在android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) 在android.app.ActivityThread.-wrap14(ActivityThread.java) 在android.app.ActivityThread $ H.handleMessage(ActivityThread.java:1635) 在android.os.Handler.dispatchMessage(Handler.java:102) 在android.os.Looper.loop(Looper.java:154) 在android.app.ActivityThread.main(ActivityThread.java:6692) 在java.lang.reflect.Method.invoke(本机方法) 在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run(ZygoteInit.java:1468) com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.lacas.asd/com.lacas.asd.ui.activities.testtabs.TestTab2Activity}: java.lang.RuntimeException: Cannot create an instance of class com.lacas.asd.db.room.BookmarkViewModel at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2924) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1635) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6692) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) Caused by: java.lang.RuntimeException: Cannot create an instance of class com.lacas.asd.db.room.BookmarkViewModel at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:207) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity$viewModel$2.invoke(TestTab2Activity.kt:34) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity$viewModel$2.invoke(TestTab2Activity.kt:29) at kotlin.UnsafeLazyImpl.getValue(Lazy.kt:154) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity.getViewModel(TestTab2Activity.kt) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity.onCreated(TestTab2Activity.kt:45) at com.lacas.asd.base.BasePermissionsActivity.onCreate(BasePermissionsActivity.kt:34) at android.app.Activity.performCreate(Activity.java:6912) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1635) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6692) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Constructor.newInstance0(Native Method) at java.lang.reflect.Constructor.newInstance(Constructor.java:430) at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:199) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity$viewModel$2.invoke(TestTab2Activity.kt:34) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity$viewModel$2.invoke(TestTab2Activity.kt:29) at kotlin.UnsafeLazyImpl.getValue(Lazy.kt:154) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity.getViewModel(TestTab2Activity.kt) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity.onCreated(TestTab2Activity.kt:45) at com.lacas.asd.base.BasePermissionsActivity.onCreate(BasePermissionsActivity.kt:34) at android.app.Activity.performCreate(Activity.java:6912) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1635) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6692) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358) Caused by: java.lang.RuntimeException: cannot find implementation for com.lacas.asd.db.room.BookmarkDb. BookmarkDb_Impl does not exist at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:93) at android.arch.persistence.room.RoomDatabase$Builder.build(RoomDatabase.java:630) at com.lacas.asd.db.room.BookmarkDb$Companion.get(BookmarkDb.kt:29) at com.lacas.asd.db.room.BookmarkViewModel.(BookmarkViewModel.kt:14) at java.lang.reflect.Constructor.newInstance0(Native Method) at java.lang.reflect.Constructor.newInstance(Constructor.java:430) at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:199) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity$viewModel$2.invoke(TestTab2Activity.kt:34) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity$viewModel$2.invoke(TestTab2Activity.kt:29) at kotlin.UnsafeLazyImpl.getValue(Lazy.kt:154) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity.getViewModel(TestTab2Activity.kt) at com.lacas.asd.ui.activities.testtabs.TestTab2Activity.onCreated(TestTab2Activity.kt:45) at com.lacas.asd.base.BasePermissionsActivity.onCreate(BasePermissionsActivity.kt:34) at android.app.Activity.performCreate(Activity.java:6912) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1126) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2877) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2985) at android.app.ActivityThread.-wrap14(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1635) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6692) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1468) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1358)
推荐答案
有人在这里说:
Android机房持久性:AppDatabase_Impl不存在
解决方案是:
实现"androidx.lifecycle:lifecycle-extensions:$ lifecycle_version" kapt"androidx.lifecycle:lifecycle-compiler:$ lifecycle_version"
implementation "androidx.lifecycle:lifecycle-extensions:$lifecycle_version" kapt "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"
implementation "androidx.room:room-runtime:$roomVersion"
kapt "androidx.room:room-compiler:$roomVersion"
implementation "androidx.paging:paging-runtime:$paging_version"
这篇关于无法创建类ViewModel kotlin的实例的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
