CODEWITHSUNDEEP
androidexceptionviewmodel
Lukas
Lukas

Reputation: 39

Android Studio: ViewModel Exception

I try creating a view model of a youtube tutorial, that's supposed to show all the entries from a database (but at this point it shoudl only display a Toast as there's no Recycler View yet)

I get the following exception when opening the activity:

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.tutorial/com.example.tutorial.Activity2}: java.lang.RuntimeException: Cannot create an instance of class com.example.tutorial.EventViewModel

......

at com.example.tutorial.Activity2.onCreate(Activity2.java:23)

Class looks as following:

public class Activity2 extends AppCompatActivity {
    private EventViewModel eventViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_2);

        eventViewModel = new ViewModelProvider(this).get(EventViewModel.class);
        eventViewModel.getAllEvents().observe(this, new Observer<List<Event>>() {
            @Override
            public void onChanged(List<Event> events) {
                Toast.makeText(Activity2.this, "thhthth", Toast.LENGTH_SHORT).show();
            }
        });

    }
}

ViewModel Class:

public class EventViewModel extends AndroidViewModel {
    private EventRepository repository;
    private LiveData<List<Event>> allEvents;

    public EventViewModel(@NonNull Application application) {
        super(application);
        repository = new EventRepository(application);
        allEvents = repository.getAllEvents();
    }

    public void insert(Event event) {
        repository.insert(event);
    }

    public void update(Event event) {
        repository.update(event);
    }

    public void delete(Event event) {
        repository.delete(event);
    }

    public LiveData<List<Event>> getAllEvents() {
        return allEvents;
    }


}

How can I fix this? (still an Android beginner btw :^) )

Thanks in advance!

Upvotes: 1

Views: 750

Answers (5)

c maly
c maly

Reputation: 1

https://stackoverflow.com/a/60857926/13614001

Android Studio - version 3.6.2

This worked for me.

Make sure you include the dependencies in the build.gradle(Module:app) and as well as the code changes.

More importantly "do the grade sync" after including the dependencies.

Upvotes: 0

AmmAr Yasser
AmmAr Yasser

Reputation: 391

because "ViewModelProviders" is deprecated, for java programmers, use this:100% gonna work

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    noteViewModel = new ViewModelProvider(this
            , ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication()))
            .get(NoteViewModel.class);

    noteViewModel.getAllNotes().observe(this, new Observer<List<Note>>() {
        @Override
        public void onChanged(List<Note> notes) {

            Toast.makeText(MainActivity.this, "Onchange ", Toast.LENGTH_SHORT).show();
        }
    });

Go to your build.gradle(Module:app)

def lifecycle_version = "2.2.0"
def room_version = "2.2.5"
implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
// LiveData
implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
annotationProcessor "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"

implementation "androidx.room:room-runtime:$room_version"
annotationProcessor "androidx.room:room-compiler:$room_version"

Upvotes: 1

CBS
CBS

Reputation: 126

This would work fine:

1.Go to your build.gradle(Module:app) and add this in the dependencies : 

`implementation "android.arch.lifecycle:extensions:$lifecycle_version"`

make sure to have the def lifecycle_version = "2.2.0" in your dependencies.
So it shoud look like this: 

dependencies {

    def lifecycle_version = "2.2.0"  //make sure to have this 

    //Some implementations ...  

    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'


    implementation "android.arch.lifecycle:extensions:$lifecycle_version" // make sure to have this too.

}

2.Go to your Activity (in your case it's the Activity2) and put this line: 

eventViewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication())).get(EventViewModel.class);

So your code should look like this: 

public class Activity2 extends AppCompatActivity {
    private EventViewModel eventViewModel;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_2);

        eventViewModel = new ViewModelProvider(this, ViewModelProvider.AndroidViewModelFactory.getInstance(this.getApplication())).get(EventViewModel.class);
        eventViewModel.getAllEvents().observe(this, new Observer<List<Event>>() {
            @Override
            public void onChanged(List<Event> events) {
                Toast.makeText(Activity2.this, "enjoy :)", Toast.LENGTH_SHORT).show();
            }
        });

    }
}

3.Run your app.

Upvotes: 4

Kelvin Herwanda Tandrio
Kelvin Herwanda Tandrio

Reputation: 140

You must define "eventViewModel" in method onCreate and don't make a general variable.

public class Activity2 extends AppCompatActivity {
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_2);

        EventViewModel eventViewModel = new ViewModelProvider(this).get(EventViewModel.class);
        ...
    }
}

Upvotes: 1

Johnny Be Good
Johnny Be Good

Reputation: 11

Your viewModel extends AndroidViewModel. Use AndroidViewModelFactory:

yourViewModel = new ViewModelProvider.AndroidViewModelFactory(getApplication()).create(YourViewModel.class);

Upvotes: 1

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