ava.lang.RuntimeException: Cannot create an instance of class com.example.bookkeepers.BookViewModel

Question

I am developing a new book android app but app crashes when I am testing the code getting following exceptions from logcat

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.bookkeepers/com.example.bookkeepers.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.example.bookkeepers.BookViewModel at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2843) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2921) at android.app.ActivityThread.-wrap11(Unknown Source:0) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1639) at android.os.Handler.dispatchMessage(Handler.java:106) at android.os.Looper.loop(Looper.java:176) at android.app.ActivityThread.main(ActivityThread.java:6662) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:547) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:873) Caused by: java.lang.RuntimeException: Cannot create an instance of class com.example.bookkeepers.BookViewModel at androidx.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:208) at androidx.l

ifecycle.ViewModelProvider.get(ViewModelProvider.java:135) at androidx.lifecycle.ViewModelProvider.get(ViewModelProvider.java:103) at com.example.bookkeepers.MainActivity.onCreate(MainActivity.kt:30) at android.app.Activity.performCreate(Activity.java:7074) at android.app.Activity.performCreate(Activity.java:7065) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2796) ... 9 more 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$AndroidViewModelFactory.create(ViewModelProvider.java:200) ... 16 more Caused by: java.lang.RuntimeException: cannot find implementation for com.example.bookkeepers.BookRoomDatabase. BookRoomDatabase_Impl does not exist at androidx.room.Room.getGeneratedImplementation(Room.java:94) at androidx.room.RoomDatabase$Builder.build(RoomDatabase.java:952) at com.example.bookkeepers.BookRoomDatabase$Companion.getDatabase(BookRoomDatabase.kt:24) at com.example.bookkeepers.BookViewModel.(BookViewModel.kt:12) ... 19 more

below my BookViewModel class which extends AndroidViewModel class

class BookViewModel(application: Application) : AndroidViewModel(application) {

private val bookDao: BookDao

init {
    val bookDb = BookRoomDatabase.getDatabase(application)

    bookDao = bookDb!!.bookDao()
}


fun insert(book: Book) {
    InsertAsyncTask(bookDao).execute(book)
}

companion object {
    private class InsertAsyncTask(private val bookDao: BookDao) :
        AsyncTask<Book, Void, Void>() {
        override fun doInBackground(vararg books: Book): Void? {
            bookDao.insert(books[0])
            return null
        }

    }
}}

below MainActivity.kt class

MainActivity : AppCompatActivity() {

 lateinit var bookViewModel: BookViewModel

override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)
    setSupportActionBar(toolbar)

    fab.setOnClickListener { view ->
        val intent =  Intent(this, NewBookActivity::class.java)
        startActivityForResult(intent, NEW_NOTE_ACTIVITY_REQUEST_CODE)
    }
   bookViewModel = ViewModelProviders.of(this).get(BookViewModel::class.java)
}


override fun onActivityResult(requestCode: Int, resultCode: Int, data: Intent?) {
    super.onActivityResult(requestCode, resultCode, data)

    if (requestCode == NEW_NOTE_ACTIVITY_REQUEST_CODE && resultCode == Activity.RESULT_OK) {
        val id = UUID.randomUUID().toString()
        val authorName = data!!.getStringExtra(NewBookActivity.NEW_AUTHOR)
        val bookName = data!!.getStringExtra(NewBookActivity.NEW_BOOK)

        val book = Book(id, authorName, bookName)
        bookViewModel.insert(book)

        Toast.makeText(
            applicationContext,
            R.string.saved,
            Toast.LENGTH_LONG
        ).show()

    } else {
        Toast.makeText(
            applicationContext,
            R.string.not_saved,
            Toast.LENGTH_LONG
        ).show()
    }
}

companion object{
    private const val NEW_NOTE_ACTIVITY_REQUEST_CODE = 1
}}

below database class

  @Database(entities = [Book::class], version = 1)
 abstract class BookRoomDatabase :RoomDatabase() {


abstract fun bookDao():BookDao


companion object {

    private var bookRoomInstance:BookRoomDatabase? = null
    fun getDatabase(context: Context): BookRoomDatabase? {
        if (bookRoomInstance == null)
            synchronized(BookRoomDatabase::class.java){
                if(bookRoomInstance == null){
                    bookRoomInstance = Room.databaseBuilder<BookRoomDatabase>(context.applicationContext,
                        BookRoomDatabase::class.java, "book_database")
                        .build()
                }
            }
    return bookRoomInstance
    }

}}

below dao class

@Dao
 interface BookDao {
  @Insert
  fun insert(book: Book)
  }

below book entity class

@Entity(tableName = "books")
class Book(@PrimaryKey val id: String,

       @ColumnInfo(name = "author")
       val author: String,
       val book:String) {
}

I've never used Room but I notice you are trying to instantiate an Abstract class, I don't think that's possible. You should have a subclass of `BookRoomDatabase` that implements the abstract functions. I think that's why you are seeing the crash, because it can't create an instance of the abstract class. — jsmyth886, Aug 25 '19 at 11:09
can you post your Gradle dependencies of the Arch Components? — Ahmed Elshaer, Aug 25 '19 at 11:21
@jsmyth886 the abstract keyword is not a problem but a requirement in Room database. Check the docs: https://developer.android.com/training/data-storage/room — Andrew Chelix, Nov 25 '20 at 12:14

score 1 · Accepted Answer · answered Aug 25 '19 at 11:27

The idea behind it that you are using kotlin and in your app build.gradle you should be applying kapt plugin apply plugin 'kotlin-kapt' and using kapt instead of annotationProcessor

implementation "android.arch.lifecycle:extensions:$lifecycle_version"
kapt "android.arch.lifecycle:compiler:$lifecycle_version"

implementation "android.arch.persistence.room:runtime:$room_version"
kapt "android.arch.persistence.room:compiler:$room_version"

Check this answer https://stackoverflow.com/a/50487165/4614550

score 1 · Answer 2 · answered Nov 25 '20 at 12:12

1

The problem is that you're trying to instantiate the ViewModel without providing the required arguments application: Application. I posted an answer that solves this issue here: https://stackoverflow.com/a/65004171/13834895.

answered Nov 25 '20 at 12:12

Andrew Chelix

1,012
11
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ava.lang.RuntimeException: Cannot create an instance of class com.example.bookkeepers.BookViewModel

2 Answers2