View pager fragments removing

Question

My activity should handle portrait and landscape layouts in different ways: if layout is portrait, then in should use ViewPager with two fragments. If layout is landscape, then it should just divide screen on two parts and locate two fragments there. The problem is that when I switch from portrait to landscape, viewpager's fragments are not removed and onCreateView() is called for them.

Calling removing fragments with FragmentTransaction does nothing.

protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewModel = ViewModelProviders.of(this).get(MainViewModel.class);
        int orientation = getResources().getConfiguration().orientation;
        if (orientation == Configuration.ORIENTATION_LANDSCAPE) {
            FragmentManager fragmentManager = getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.weather_layout, new CurrentWeatherFragment(), "current");
            fragmentTransaction.replace(R.id.forecast_layout, new ForecastFragment(), "forecast");
            fragmentTransaction.commit();
        }
        else {
            ViewPager viewPager = findViewById(R.id.pager);
            WeatherPageAdapter weatherPageAdapter = new WeatherPageAdapter(getSupportFragmentManager());
            viewPager.setAdapter(weatherPageAdapter);
            viewPager.addOnPageChangeListener(new WeatherPageChangedListener());
            viewPager.setCurrentItem(viewModel.getViewPagerPosition(), false);
        }
    }

import androidx.fragment.app.Fragment;
import androidx.fragment.app.FragmentManager;
import androidx.fragment.app.FragmentPagerAdapter;
import com.example.android.myapplication.ui.fragments.CurrentWeatherFragment;
import com.example.android.myapplication.ui.fragments.ForecastFragment;

public class WeatherPageAdapter extends FragmentPagerAdapter {
    private static final int pageNumber = 2;

    public WeatherPageAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    }

    @Override
    public int getCount() {
        return pageNumber;
    }

    @Override
    public Fragment getItem(int i) {
        if (i == 0) {
            return new CurrentWeatherFragment();
        }
        else {
            return new ForecastFragment();
        }
    }
}

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:rowCount="7"
    android:columnCount="2"
    tools:context=".ui.activities.MainActivity">

    <androidx.viewpager.widget.ViewPager
            android:id="@+id/pager"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

</LinearLayout>

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:rowCount="7"
    android:columnCount="2"
    tools:context=".ui.activities.MainActivity"
    android:orientation="horizontal"
    android:baselineAligned="false">

    <FrameLayout
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:id="@+id/weather_layout">
    </FrameLayout>

    <FrameLayout
            android:layout_width="0dp"
            android:layout_height="match_parent"
            android:layout_weight="1"
            android:id="@+id/forecast_layout">
    </FrameLayout>

</LinearLayout>

Answer 1

In your earlier code, Do the following modification:

private ViewPager viewPager;
private WeatherPageAdapter weatherPageAdapter;


protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        viewModel = ViewModelProviders.of(this).get(MainViewModel.class);
        changeViewAsPerOrientation(getResources().getConfiguration().orientation);
    }

private void changeViewAsPerOrientation(Configuration newConfig) {
      for (Fragment fragment : getSupportFragmentManager().getFragments()) {
            getSupportFragmentManager().beginTransaction().remove(fragment).commit();
        }
      if (newConfig.orientation == Configuration.ORIENTATION_LANDSCAPE) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.weather_layout, new CurrentWeatherFragment(), "current");
        fragmentTransaction.replace(R.id.forecast_layout, new ForecastFragment(), "forecast");
        fragmentTransaction.commit();
      }
      else {
         if(viewPager == null || weatherPageAdapter == null) {
          viewPager = findViewById(R.id.pager);
          weatherPageAdapter = new  WeatherPageAdapter(getSupportFragmentManager());
          viewPager.addOnPageChangeListener(new WeatherPageChangedListener());
        } else {
          adapter.notifyDataSetChanged();
        }

        viewPager.setCurrentItem(viewModel.getViewPagerPosition(), false);
      }
    }

@Override
  public void onConfigurationChanged(Configuration newConfig) {
    super.onConfigurationChanged(newConfig);
    changeViewAsPerOrientation(newConfig);
  }