Cannot create an instance of class ViewModel kotlin

Question

Here is my code

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)
    }
}

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)
...

And here is the problem:

java.lang.RuntimeException: Cannot create an instance of class com.lacas.db.room.BookmarkViewModel

Can I use this in a fragment?

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) 

Answer 1

As somebody said here:

Android room persistent: AppDatabase_Impl does not exist

the solution was:

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"