Search code examples
javaandroidbottomnavigationview

Android drawing app intended for a single View needs to work in multi-view Bottom Navigation Activity app

I'm a completely new Android dev and am rather lost at the moment. I'm following this tutorial as I try to enable drawing to a view in my app which is a "Bottom Navigation Activity" project that features three tabs--or fragments. See screenshot below:

enter image description here

The problem is that the tutorial is intended for an app with a single View and a single standard MainActivity. In this case, the following code is used in the onCreate()method in the project's MainActivity.java class:

public class MainActivity extends AppCompatActivity {
super.onCreate(savedInstanceState):
PaintView paintView = new PaintView(content: this):
setContentView(paintView);
  }

}

When I build a single view app, the code works great. No issues. But things can't work in my "Bottom Navigation Activity" project, because the fragments use a ViewModel type that doesn't offer the much needed methods of the View class. My app features 3 fragments, the first of which is named HomeFragment. It is on this fragment that I want all my drawing to take place. The default onCreateView() method for this fragment looks like so:

public class HomeFragment extends Fragment {

private HomeView Model homeViewModel;

public View onCreateView(@NonNull LayoutInflator inflater, ViewGroup container, Bundle savedInstanceState) {

homeViewModel = ViewModelProviders.of(fragment: this).get(HomeViewModel.class);
View root = inflater.inflate(R.layout.fragment_home, container, attachToRoot: false);

return root;
 }
}

See screenshot below to see what I've tried to do. You will see that I've added a View class to my project called PaintView (just as created in the tutorial), which contains all the drawing code.

enter image description here

Unfortunately it generates the following compilation error:

Inferred type com.example.mobile_testapp_android_2_ui.home.PaintView for type parameter T is not within its bound; should extend androidx.lifecycle.ViewModel

Any tips on how I can implement the tutorial's PaintView class so that I can use its methods to draw on the "HomeFragment" would be deeply appreciated.

Thank you and very cordially,

Wulf

Solution

  • What you are doing is trying to create a HomeViewModel object with the PaintView class which is not possible. If you want to set PaintView as the view of your HomeFragment, you need to return an object of it as :

        //you can return any kind of view object as you like
    public View onCreateView(@NonNull LayoutInflator inflater, ViewGroup container, Bundle savedInstanceState) {

        PaintView homeFragmentView = new PaintView(requireContext());

        // PaintView class must extends View class
        return homeFragmentView;

    }

    I hope, this helps.

    Learn more about Fragment here

    Learn more about ViewModel here