title: Switch activity/fragment with bottom navigation
body: <p>I created an activity with a bottom navigation bar.
  I googled a lot things about it but now I don't know how to handle this exactly.
  Before, I just started another activity when the user clicks the bottom navigation but I think it's not good.</p>
  
  <p>How can I switch between the tabs?
  Do I have to work with fragments? And what about 'setContentView(int layoutResID)'? How can I do that? I'm confused...</p>
  
  <pre><code>private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener = new BottomNavigationView.OnNavigationItemSelectedListener() {
  
      @Override
      public boolean onNavigationItemSelected(@NonNull MenuItem item) {
          switch (item.getItemId()) {
              case R.id.navigation_home:
                  return true;
              case R.id.navigation_dashboard:
                  startActivity(dashboardActivity);
                  return true;
              case R.id.navigation_notifications:
                  startActivity(dashboardActivity);
                  return true;
          }
          return false;
      }
  
  };
  </code></pre>
  
  <p>Thank you very much for your help - I hope, you understood what I mean.</p>