CODEWITHSUNDEEP
javaandroidviewmodelandroid-livedata
Nouras
Nouras

Reputation: 129

Android LiveData, Cannot create an instance of class viewModel

Following the example given by android, I extended the ViewModel class 

public class NameViewModel extends ViewModel {
private MutableLiveData<String> currentName;

public MutableLiveData<String> getCurrentName() {
    if (currentName == null) {
        currentName = new MutableLiveData<String>();
    }
    return currentName;
}}

and i observed the LiveData objects

public class NameActivity extends AppCompatActivity {

private NameViewModel model;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    // Other code to setup the activity...

    // Get the ViewModel.
    model = new ViewModelProvider(this).get(NameViewModel.class);

    // Create the observer which updates the UI.
    final Observer<String> nameObserver = new Observer<String>() {
        @Override
        public void onChanged(@Nullable final String newName) {
            // Update the UI, in this case, a TextView.
            nameTextView.setText(newName);
        }
    };

    // Observe the LiveData, passing in this activity as the LifecycleOwner and the observer.
    model.getCurrentName().observe(this, nameObserver);
}}

and my dependencies in build.gradle are

dependencies {
    def lifecycle_version = "2.2.0"

    implementation fileTree(dir: 'libs', include: ['*.jar'])

    implementation 'androidx.appcompat:appcompat:1.0.2'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'

    // ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel:$lifecycle_version"
    // LiveData
    implementation "androidx.lifecycle:lifecycle-livedata:$lifecycle_version"
    // Lifecycles only (without ViewModel or LiveData)
    implementation "androidx.lifecycle:lifecycle-runtime:$lifecycle_version"


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

Running this code is giving Cannot create an instance of class NameViewModel, what am I doing wrong in here?

Upvotes: 0

Views: 620

Answers (5)

Дмитрий Резанов
Дмитрий Резанов

Reputation: 1

Instead: model = new ViewModelProvider(this).get(NameViewModel.class);

Try this: model = new ViewModelProvider(this,new ViewModelProvider.AndroidViewModelFactory(getApplication())).get(NameViewModel.class);

Upvotes: 0

tomasvalkering
tomasvalkering

Reputation: 26

You are missing the constructor in the ViewModel class, so add public NameViewModel() {}; to your ViewModel.

Upvotes: 1

Nouras
Nouras

Reputation: 129

I had NameViewModel in the same java file as NameActivity, where it should be in separate file NameViewModel.java, this fixed it.

Upvotes: 0

Some random IT boy
Some random IT boy

Reputation: 8477

Should you, perhaps, add an empty constructor in the ViewModel an call super() there?

Upvotes: 0

Amit Gupta
Amit Gupta

Reputation: 51

Nothing seems to be wrong with the code though.

Could you check if you have this particular dependency version in your build.gradle

 implementation 'androidx.lifecycle:lifecycle-viewmodel-ktx:2.2.0'

and could you please add your build.gradle .

Upvotes: 0

Related Questions