Wsrtjtyk

I am new to programming. I have 4 working activities with 4 xml layouts. I also copied this simple example fragment (I think I need 4 of those for my 4 activites) from a tutorial:

public class SelectFriends extends Fragment {





    public SelectFriends () {

        // Required empty public constructor

    }





    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        return inflater.inflate(R.layout.fragment_SelectFriends , container, false);

    }



}

This is the relevant part from MainActivity:

 @Override

    public boolean onNavigationItemSelected(@NonNull MenuItem item) {



        switch (item.getItemId()){

            case R.id.navigation_item1:

                getSupportFragmentManager().beginTransaction().setCustomAnimations(R.anim.fade_in, R.anim.fade_out).replace(R.id.container, SelectFriends).commit();

                return true;



            case R.id.navigation_item2:

                getSupportFragmentManager().beginTransaction().setCustomAnimations(R.anim.fade_in, R.anim.fade_out).replace(R.id.container, StartFood).commit();

                return true;

[...]



        }

        return false;

    }

I can start my activitie´s selectFriends.xml when I replace fragment_SelectFriends in @Override public View onCreateView with ID of selectFriends.xml . The problem is I don´t know where to put the corresponding Activity, so the selectFriends.xml shows up correctly with BottomNavigation but there is no interaction possible, of course. What is best practice? Internet is confusing me: am I understanding the use of fragments false? I don´t even understand why I should make fragments with BottomNavigation when the things I want to show in the different BottomNavigation displays are completely different from each other. Thank you

Let's start from your question:

How to correctly put my activities in Tutorial´s Bottom Navigation?

You will not put your activities in the Bottom Navigation.

You will have one Activity which will draw the layout of your screen. Secondly you will have a number of Fragment's which will represent some parts of your screen.

How many Fragment's? As many as the Bottom Navigation's options.
Take the Youtube app as an example.

The whole screen is an Activity, Youtube's MainActivity. As you can see the user pressed Subscriptions in the Bottom Navigation so the MainActivity called a SubscriptionsFragment to draw the subscriptions part of the screen (all the layout except the ActionBar at the top and the Bottom Navigation at the bottom.

If a user selects Home at the Bottom Navigation then the MainActivity will replace the part of the screen where the SubscriptionsFragment draw its layout with the HomeFragment's layout. And the same thing will happen with the other options of Youtube's Bottom Navigation bar.

So to clarify. There is only one activity here. The MainActivity. Not four. This activity commands 4 fragments to draw the 4 main parts of its screen (the home part with HomeFragment, the trending part with TrendingFragment, the subscription part with SubscriptionFragment and finally the library part with LibraryFragment.

From your last comment:

I have to put the two pieces of code that I posted above into one big
class?

No you don't have to. It is not necessary to create one file, such as MainActivity.java (where your MainActivity is defined), and then define the Fragment's classes inside the same file.

You want to display 4 screens using a bottom navigation, right? Create a file for your activity and four separate files, one per Fragment.

Example:

Your first file, SelectFriends.java, where SelectFriends fragment is defined, as you've posted above...

public class SelectFriends extends Fragment {





    public SelectFriends () {

        // Required empty public constructor

    }





    @Override

    public View onCreateView(LayoutInflater inflater, ViewGroup container,

                             Bundle savedInstanceState) {

        // Inflate the layout for this fragment

        return inflater.inflate(R.layout.fragment_SelectFriends , container, false);

    }



}

Three more separate files like this one, one per fragment.

And lastly your activity, again, as you've posted above.

public class MainActivity extends AppCompatActivity{



    @Override

    public void onCreate(Bundle savedInstanceState){

      // ... some code here

    }



    @Override

        public boolean onNavigationItemSelected(@NonNull MenuItem item) {



            switch (item.getItemId()){

                case R.id.navigation_item1:

                    ..

                // Here the activity figured out that the first item of the bottom navigation

                // was clicked, so it calls the support fragment manager to display a fragment

                // inside the container view

                    getSupportFragmentManager().beginTransaction()

                    .setCustomAnimations(R.anim.fade_in, R.anim.fade_out)

                    .replace(R.id.container, SelectFriends).commit();

                    return true;



                case R.id.navigation_item2:

                    getSupportFragmentManager().beginTransaction()

                    .setCustomAnimations(R.anim.fade_in, R.anim.fade_out)

                    .replace(R.id.container, StartFood).commit();

                    return true;

            }

            return false;

        }

    } 

Edit: Read the Ultimate Guide to Bottom Navigation on Android