我是一个很新的android开发。我想隐藏导航抽屉时，用户没有登录。所以基本上，它会显示登录片段（更好地在全屏像Facebook android）。如果用户已经登录，导航抽屉将始终显示。
MainActivity.java

public class MainActivity extends AppCompatActivity {

private DrawerLayout navDrawerLayout;
private Toolbar toolbar;
private ActionBarDrawerToggle navDrawerToggle;

private SharedPreferences pref;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    toolbar = (Toolbar) findViewById(R.id.toolbar);
    setSupportActionBar(toolbar);

    navDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);

    // Find our drawer view
    NavigationView navDrawerView = (NavigationView) findViewById(R.id.navdrawer_view);
    // Setup drawer view
    setupDrawerContent(navDrawerView);

    navDrawerToggle = setupDrawerToggle();

    pref = getPreferences(0);
    initFirstFrame();
}

private ActionBarDrawerToggle setupDrawerToggle() {
    return new ActionBarDrawerToggle(this, navDrawerLayout, toolbar, R.string.drawer_open,  R.string.drawer_close);
}

private void setupDrawerContent(NavigationView navDrawerView) {
    navDrawerView.setNavigationItemSelectedListener(
            new NavigationView.OnNavigationItemSelectedListener() {
                @Override
                public boolean onNavigationItemSelected(MenuItem menuItem) {
                    selectDrawerItem(menuItem);
                    return true;
                }

            });
}

public void selectDrawerItem(MenuItem menuItem) {
    // Create a new fragment and specify the fragment to show based on nav item clicked
    Fragment fragment = null;
    Class fragmentClass;
    switch(menuItem.getItemId()) {
        case R.id.events:
            fragmentClass = EventsFragment.class;
            break;
        case R.id.pengumuman:
            fragmentClass = NewsFragment.class;
            break;
        case R.id.edit_profil:
            fragmentClass = ProfileFragment.class;
            break;
        default:
            fragmentClass = EventsFragment.class;
    }

    try {
        fragment = (Fragment) fragmentClass.newInstance();
    } catch (Exception e) {
        e.printStackTrace();
    }

    // Insert the fragment by replacing any existing fragment
    FragmentManager fragmentManager = getSupportFragmentManager();
    fragmentManager.beginTransaction().replace(R.id.frame_content, fragment).commit();

    // Highlight the selected item has been done by NavigationView
    menuItem.setChecked(true);
    // Set action bar title
    setTitle(menuItem.getTitle());
    // Close the navigation drawer
    navDrawerLayout.closeDrawers();
}

private void initFirstFrame(){
    Fragment fragment;
    if(pref.getBoolean(Constants.IS_LOGGED_IN,false)){
        fragment = new ProfileFragment();
    }else {
        fragment = new LoginFragment();
        // in this login fragment, navdrawer should be invisible, the toolbar too I guess
    }

    FragmentManager fragmentManager = getSupportFragmentManager();
    FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
    fragmentTransaction.replace(R.id.frame_content,fragment);
    fragmentTransaction.commit();
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    return navDrawerToggle.onOptionsItemSelected(item) || super.onOptionsItemSelected(item);
}

// 'onPostCreate' called when activity start-up is complete after 'onStart()'
// NOTE! Make sure to override the method with only a single 'Bundle' argument
@Override
protected void onPostCreate(Bundle savedInstanceState) {
    super.onPostCreate(savedInstanceState);
    // Sync the toggle state after onRestoreInstanceState has occurred
    navDrawerToggle.syncState();
}

@Override
public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    // Pass any configuration change to the drawer toggles
    navDrawerToggle.onConfigurationChanged(newConfig);
}

}