ViewModel has no zero argument constructor error - even when it has a zero argument constructor

Question

I'm new to Android and Java and am trying to make a location-based app.

EDIT

I've made a much, much simpler test code and get the same error. Here's the java:

package com.example.viewmodeltest;

import androidx.appcompat.app.AppCompatActivity;
import androidx.lifecycle.ViewModel;
import androidx.lifecycle.ViewModelProvider;

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    public class MyViewModel extends ViewModel {
        public int scoreTeamA = 0;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        MyViewModel locationViewModel = new ViewModelProvider(this).get(MyViewModel.class);
    }
}

I get the same error. Here are the dependencies in my app-level build.gradle:

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

    implementation 'androidx.appcompat:appcompat:1.1.0'
    implementation 'androidx.constraintlayout:constraintlayout:1.1.3'
    testImplementation 'junit:junit:4.12'
    androidTestImplementation 'androidx.test.ext:junit:1.1.1'
    androidTestImplementation 'androidx.test.espresso:espresso-core:3.2.0'

    //dependencies for ViewModel, LiveData, etc.
    def lifecycle_version = "2.2.0"
    def arch_version = "2.1.0"

    // 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:$lifecycle_version"
    // Saved state module for ViewModel
    implementation "androidx.lifecycle:lifecycle-viewmodel-savedstate:$lifecycle_version"
    // Annotation processor
    annotationProcessor "androidx.lifecycle:lifecycle-compiler:$lifecycle_version"
}

ORIGINAL POST

I'm attempting to use ViewModel and LiveData to update the user location as I understand that's the best way to be lifecycle-aware. I have a default maps activity...

public class MapsActivity extends AppCompatActivity implements OnMapReadyCallback {...}

A class which extends LiveData to store the user location...

public class LocationLiveData extends LiveData<Location> {
        private final Context context;
        private FusedLocationProviderClient fusedLocationClient;
        private LocationRequest locationRequest;

        public LocationLiveData(Context context) {
            this.context = context;
            this.fusedLocationClient = LocationServices.getFusedLocationProviderClient(context);
        }

        private void setLocationData(Location location) {
            Location value = new Location("SetInternal");
            value.setLatitude(location.getLatitude());
            value.setLongitude(location.getLongitude());
            setValue(value);
        }

        protected void createLocationRequest() {
            LocationRequest locationRequest = LocationRequest.create();
            locationRequest.setInterval(1000);
            locationRequest.setFastestInterval(500);
            locationRequest.setPriority(LocationRequest.PRIORITY_HIGH_ACCURACY);
        }

        private LocationCallback locationCallback = new LocationCallback() {
            @Override
            public void onLocationResult(LocationResult locationResult) {
                if (locationResult == null) {
                    return;
                }
                for (Location location : locationResult.getLocations()) {
                    setLocationData(location);
                }
            }
        };

        private void startLocationUpdates() {
            createLocationRequest();
            fusedLocationClient.requestLocationUpdates(locationRequest,
                    locationCallback,
                    Looper.getMainLooper());
        }

        @Override
        protected void onInactive() {
            super.onInactive();
            fusedLocationClient.removeLocationUpdates(locationCallback);
        }

        @Override
        protected void onActive() {
            super.onActive();
            fusedLocationClient.getLastLocation()
                    .addOnSuccessListener(new OnSuccessListener<Location>() {
                        @Override
                        public void onSuccess(Location location) {
                            if (location != null)
                                setValue(location);
                        }
                    });
            startLocationUpdates();
        }
    }

And a class which extends ViewModel to allow the main activity to reach the LocationLiveData.

 public class LocationViewModel extends ViewModel {
        private LocationLiveData locationLiveData;

        public LocationViewModel () {
            locationLiveData = new LocationLiveData(getApplicationContext());
        }

        public LocationLiveData getLocationLiveData() {
            return locationLiveData;
        }
    }

Then when I attempt to make an instance of locationViewModel in the onMapReady method:

LocationViewModel locationViewModel = new ViewModelProvider(this).get(LocationViewModel.class);

I get an error on that line:

Cannot create an instance of class com.example.MapsActivity$LocationViewModel

Caused by: java.lang.InstantiationException: java.lang.Class has no zero argument constructor

I get this error even if I take out the constructor entirely in locationViewModel, and also if I attempt to extend AndroidViewModel instead.

Any ideas? I've seen other similar queries but the answer has always been to take arguments out of the constructor - which I've already done!

Thanks a lot for any help

Answer 1

while using hilt I am facing the same issue when I forgot to add

@AndroidEntryPoint

above the activity declaration