Cannot create an instance of class ViewModel : <p>I am trying to write a sample app using Android architecture components and but even after trying for days I could not get it to work. It gives me the above exception.</p>

<p>Lifecycle owner:-</p>

<pre><code>public class MainActivity extends LifecycleActivity {

    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        TextView textView = findViewById(R.id.tv_user);
        PostViewModel viewModel = ViewModelProviders.of(this).get(PostViewModel.class);
        viewModel.loadPosts();
        viewModel.getPost().observe(this, new Observer&lt;Post&gt;() {
            @Override
            public void onChanged(@Nullable Post post) {
                if(post != null) {
                    textView.setText(post.toString());
                }
            }
        });
    }
}
</code></pre>

<p>ViewModel:-</p>

<pre><code>public class PostViewModel extends ViewModel {
    private MediatorLiveData&lt;Post&gt; post;
    private PostRepository postRepo;

    PostViewModel() {
        post = new MediatorLiveData&lt;&gt;();
        postRepo = new PostRepository();
    }

    public LiveData&lt;Post&gt; loadPosts() {
        post.addSource(postRepo.getPost(),
                post -&gt; this.post.setValue(post)
        );
        return post;
    }

    @NonNull
    public LiveData&lt;Post&gt; getPost() {
        return post;
    }
}
</code></pre>
