Cannot create an instance of subclass of AndroidViewModel

Question

My ViewModel class is in Java and my Activity class is in Kotlin. I am getting the error

09-18 14:01:32.737 14082-14082/com.meme.archcompwordlist E/AndroidRuntime: FATAL EXCEPTION: main Process: com.meme.archcompwordlist, PID: 14082 java.lang.RuntimeException: Unable to start activity ComponentInfo{com.meme.archcompwordlist/com.meme.archcompwordlist.MainActivity}: java.lang.RuntimeException: Cannot create an instance of class com.meme.archcompwordlist.WordViewModel at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2665) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726) at android.app.ActivityThread.-wrap12(ActivityThread.java) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:154) at android.app.ActivityThread.main(ActivityThread.java:6119) at java.lang.reflect.Method.invoke(Native Method) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776) Caused by: java.lang.RuntimeException: Cannot create an instance of class com.meme.archcompwordlist.WordViewModel at android.arch.lifecycle.ViewModelProvider$AndroidViewModelFactory.create(ViewModelProvider.java:207) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:134) at android.arch.lifecycle.ViewModelProvider.get(ViewModelProvider.java:102) at com.meme.archcompwordlist.MainActivity.onCreate(MainActivity.kt:37) at android.app.Activity.performCreate(Activity.java:6679) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)  at android.app.ActivityThread.-wrap12(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6119)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)  Caused by: java.lang.reflect.InvocationTargetException at java.lang.reflect.Constructor.newInstance0(Native Method) at java.lang.reflect.Constructor.newInstance(Constructor.java:430) at android.arch.lifecycle.ViewModelProvider$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.meme.archcompwordlist.MainActivity.onCreate(MainActivity.kt:37)  at android.app.Activity.performCreate(Activity.java:6679)  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)  at android.app.ActivityThread.-wrap12(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6119)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)  Caused by: java.lang.RuntimeException: cannot find implementation for com.meme.archcompwordlist.room.WordRoomDatabase. WordRoomDatabase_Impl does not exist at android.arch.persistence.room.Room.getGeneratedImplementation(Room.java:93) at android.arch.persistence.room.RoomDatabase$Builder.build(RoomDatabase.java:630) at com.meme.archcompwordlist.room.WordRoomDatabase.getRoomDatabase(WordRoomDatabase.java:22) at com.meme.archcompwordlist.WordRepository.(WordRepository.java:21) at com.meme.archcompwordlist.WordViewModel.(WordViewModel.java:22) at java.lang.reflect.Constructor.newInstance0(Native Method)  at java.lang.reflect.Constructor.newInstance(Constructor.java:430)  at android.arch.lifecycle.ViewModelProvider$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.meme.archcompwordlist.MainActivity.onCreate(MainActivity.kt:37)  at android.app.Activity.performCreate(Activity.java:6679)  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1118)  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2618)  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2726)  at android.app.ActivityThread.-wrap12(ActivityThread.java)  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1477)  at android.os.Handler.dispatchMessage(Handler.java:102)  at android.os.Looper.loop(Looper.java:154)  at android.app.ActivityThread.main(ActivityThread.java:6119)  at java.lang.reflect.Method.invoke(Native Method)  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:886)  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:776)

Here is my AndroidViewModel class

public class WordViewModel extends AndroidViewModel {

    private WordRepository repository;

    private LiveData<List<WordEntity>> allWords;

    public WordViewModel(Application application){
        super(application);
        repository = new WordRepository(application);
        allWords = repository.getAllWords();
    }

    public LiveData<List<WordEntity>> getAllWords(){
        return allWords;
    }

    public void insert(WordEntity word){
        repository.insert(word);
    }

    public void deleteAllWords() {
        repository.deleteAllWords();
    }
}

And here is my activity class

class MainActivity : AppCompatActivity() {

    private lateinit var wordViewModel:WordViewModel
    private lateinit var newWord:EditText
    private lateinit var recyclerView:RecyclerView
    private lateinit var adapter:WordAdapter


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

        adapter= WordAdapter()
        recyclerView= findViewById<RecyclerView>(R.id.wordList)
        recyclerView.adapter=adapter

        //establish a connection to the current ViewModel
        wordViewModel= ViewModelProviders.of(this).get(WordViewModel::class.java)

        newWord = findViewById<EditText>(R.id.insertWord);
        findViewById<Button>(R.id.submitWord).setOnClickListener {
             fun onClick(v:View?){
                if(!TextUtils.isEmpty(newWord.getText())){
                    wordViewModel.insert(WordEntity(newWord.getText().toString()))
                }
            }
        }
        findViewById<Button>(R.id.deleteWords).setOnClickListener{
            fun onClick(v:View?){
                wordViewModel.deleteAllWords()
            }
        }


        wordViewModel.getAllWords().observe(this,Observer<List<WordEntity>>(){
            fun onChanged(words:List<WordEntity>){
            adapter.setWords(words)
        }
        })

    }

}

Could someone please help me identify what I am doing wrong? I am trying to pick-up Architecture Components after a long time away from Android. I am not entirely clear how to proceed.

Answer 1

I met the same problem and find resolution from How to fix 'Cannot create an instance of ViewModel class'?

You should pass a ViewModelProvider.AndroidViewModelFactory to ViewModelProvider as follow:

WordViewModel model = new ViewModelProvider(this, new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(WordViewModel.class);