底部导航和碎片娱乐

Question

I have a bottom navigation which runs on my Main Activity

private void BottomNavigation_NavigationItemSelected(object sender, BottomNavigationView.NavigationItemSelectedEventArgs e)
{
 LoadFragment(e.Item.ItemId);
}

void LoadFragment(int id)
{
 Android.Support.V4.App.Fragment fragment = null;
 switch (id)
  {
  case Resource.Id.navigation_1:                    
  fragment = Fragment1.NewInstance();
  break;
  case Resource.Id.navigation_2:
  fragment = Fragment2.NewInstance();
  break;
  case Resource.Id.navigation_3:
  fragment = Fragment3.NewInstance();
  break;
 }
if (fragment == null)
return;

SupportFragmentManager.BeginTransaction()                
.Replace(Resource.Id.content_frame, fragment)
.Commit();
}

In my Fragment1 (which is Resource.Id.navigation_1 ) I am refreshing data

public async override void OnCreate(Bundle savedInstanceState)
{
  base.OnCreate(savedInstanceState);           
  RefreshItems(false);                    
}

The issue is, every time I click on navigation_1 for fragment1 , the data gets refreshed.

I don't want to load the fragment/data again once it's already loaded.

Is it possible in Xamarin?

Answer 1

You can check if current fragment also executed Here is a function

public Fragment find(String identifier) {
    Fragment fragment = (Fragment) getSupportFragmentManager().findFragmentByTag(identifier);
    return fragment;
}

and in BottomNavigationView you must check like this

if (find(fragment.getIdentifier()) != null) {
            return;
        }

Answer 2

I'd this problem sometime ago, however I was developing on native kotlin code, here goes the code I've used to handle this:

class Navigation(val supportFragmentManager: FragmentManager,
                 val filterIcon: ImageView ): BottomNavigationView.OnNavigationItemSelectedListener {

    override fun onNavigationItemSelected(item: MenuItem): Boolean {
        when(item.itemId){
            R.id.menu_bottom_home ->{
                changeFragment(HomeFragment(), Constants.FRAG_HOME_FRAGMENT)
                filterIcon.visibility = View.VISIBLE
            }

            R.id.menu_bottom_favorites ->{
                changeFragment(FavoritesFragment(), Constants.FRAG_FAVORITES_FRAGMENT)
                filterIcon.visibility = View.INVISIBLE
            }

            R.id.menu_bottom_reservations ->{
                changeFragment(ReservationFragment(), Constants.FRAG_RESERVATION_FRAGMENT)
                filterIcon.visibility = View.INVISIBLE
            }

            R.id.menu_bottom_profile ->{
                changeFragment(ProfileFragment(), Constants.FRAG_PROFILE_FRAGMENT)
                filterIcon.visibility = View.INVISIBLE
            }
        }

        return true
    }

    fun changeFragment(fragment: Fragment, tag : String){
        var contains: Fragment? = null
        var current: Fragment? = null
        if(supportFragmentManager.fragments != null &&  supportFragmentManager.fragments.isNotEmpty()) {
            contains = supportFragmentManager.fragments.firstOrNull { x -> x.tag == tag }
            current = supportFragmentManager.fragments.first { x -> x.isVisible }
        }

        if(current != null){
            supportFragmentManager.beginTransaction()
                    .hide(current).commit()

        }

        if(contains != null){
            supportFragmentManager.beginTransaction()
                    .show(contains).commit()
        }
        else{
            supportFragmentManager.beginTransaction()
                    .add(R.id.fl_fragment_container, fragment, tag)
                    .addToBackStack(tag)
                    .commit()
        }
    }
}

Then you just have to set setOnNavigationItemSelectedListener with your Navigation class like this:

bnv_navigation.setOnNavigationItemSelectedListener(Navigation(supportFragmentManager, iv_filter_bar))