i'm using a template for a navigation menu provided by android studio and i noticed the main activity sets the content view to a root view but I'm not sure which XML file that would be? I'm assuming it might be the XML view that first loads when i run the app (which would be fragment_home.xml) but I'm not sure if there's any specific code that is placed within an xml or java file for the root view?

this is the code for the main activity.java:

public class MainActivity extends AppCompatActivity {

    private AppBarConfiguration mAppBarConfiguration;
    private ActivityMainBinding binding;

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

        /*
        1. ON CREATE, SET MAIN SCREEN TO

        here instead of setting the main screen with findViewById, we are using BINDING!
        this is part of android jetpack!
         */
        binding = ActivityMainBinding.inflate(getLayoutInflater());  // inflate method creates an instance of the binding class for this activity to use
        setContentView(binding.getRoot());   // getRoot: a reference to the root view and passing it to setcontentview to make it the active view on the screen
                                             // when running the app, fragment_home shows up first. hence, this is the root view

        setSupportActionBar(binding.appBarMain.toolbar);
        binding.appBarMain.fab.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
                        .setAction("Action", null).show();
            }
        });
        DrawerLayout drawer = binding.drawerLayout;
        NavigationView navigationView = binding.navView;

        // Passing each menu ID as a set of Ids because each menu should be considered as top level destinations.
        mAppBarConfiguration = new AppBarConfiguration.Builder(R.id.nav_home, R.id.nav_gallery, R.id.nav_slideshow)
                .setOpenableLayout(drawer)
                .build();
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main);
        NavigationUI.setupActionBarWithNavController(this, navController, mAppBarConfiguration);
        NavigationUI.setupWithNavController(navigationView, navController);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onSupportNavigateUp() {
        NavController navController = Navigation.findNavController(this, R.id.nav_host_fragment_content_main);
        return NavigationUI.navigateUp(navController, mAppBarConfiguration)
                || super.onSupportNavigateUp();
    }
} 

and a pic of the structure of the project:

CodePudding user response：

activity_main.xml

The ActivityMainBinding is generated by viewbinding/databinding and if you cmd/ctrl click on it, it will bring you to activity_main.xml