【ANDROID STUDIO】 Fragment Communication

package com.example.fragmentcommunication;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

public class DetailFragment extends Fragment {

    public static String KEY_COUNTRY_NAME = "KEY_COUNTRY_NAME";


    @Override
    public View onCreateView(LayoutInflater inflater,
                             ViewGroup container,
                             Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_detail, container, false);
    }

    @Override
    public void onViewCreated(@NonNull View view, @Nullable Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        Bundle bundle = getArguments();

        if (bundle != null && bundle.containsKey(KEY_COUNTRY_NAME)) {
            showSelectedCountry(bundle.getString(KEY_COUNTRY_NAME));
        }
    }

    public void showSelectedCountry(String countryName) {
        ((TextView) getView().findViewById(R.id.textViewCountryName)).setText(countryName);
    }
}

package com.example.fragmentcommunication;

import androidx.appcompat.app.AppCompatActivity;
import androidx.fragment.app.FragmentTransaction;

import android.os.Bundle;
import android.widget.FrameLayout;

public class MainActivity extends AppCompatActivity {

   boolean mDualPane;

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

       setContentView(R.layout.activity_main);

       MasterFragment masterFragment = null;
       FrameLayout frameLayout = findViewById(R.id.frameLayout);
       if (frameLayout != null) {
           mDualPane = false;
           FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
           masterFragment = (MasterFragment) getSupportFragmentManager()
                   .findFragmentByTag("MASTER");
           if (masterFragment == null) {
               masterFragment = new MasterFragment();
               fragmentTransaction.add(R.id.frameLayout, masterFragment, "MASTER");
           }
           DetailFragment detailFragment = (DetailFragment)
                   getSupportFragmentManager().findFragmentById(R.id.frameLayoutDetail);
           if (detailFragment != null) {
               fragmentTransaction.remove(detailFragment);
           }
           fragmentTransaction.commit();
       } else {
           mDualPane = true;
           FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
           masterFragment = (MasterFragment) getSupportFragmentManager()
                   .findFragmentById(R.id.frameLayoutMaster);
           if (masterFragment == null) {
               masterFragment = new MasterFragment();
               fragmentTransaction.add(R.id.frameLayoutMaster, masterFragment);
           }
           DetailFragment detailFragment = (DetailFragment) getSupportFragmentManager()
                   .findFragmentById(R.id.frameLayoutDetail);
           if (detailFragment == null) {
               detailFragment = new DetailFragment();
               fragmentTransaction.add(R.id.frameLayoutDetail, detailFragment);
           }
           fragmentTransaction.commit();
       }
       masterFragment.setOnMasterSelectedListener(new MasterFragment.OnMasterSelectedListener() {
           @Override
           public void onItemSelected(String countryName) {
               sendCountryName(countryName);
           }
       });
   }


   private void sendCountryName(String countryName) {
       DetailFragment detailFragment;
       if (mDualPane) {
           //Two pane layout
           detailFragment = (DetailFragment) getSupportFragmentManager().findFragmentById(R.id.frameLayoutDetail);
           detailFragment.showSelectedCountry(countryName);
       } else {
           // Single pane layout
           detailFragment = new DetailFragment();
           Bundle bundle = new Bundle();
           bundle.putString(DetailFragment.KEY_COUNTRY_NAME, countryName);
           detailFragment.setArguments(bundle);
           FragmentTransaction fragmentTransaction = getSupportFragmentManager().beginTransaction();
           fragmentTransaction.replace(R.id.frameLayout, detailFragment);
           fragmentTransaction.addToBackStack(null);
           fragmentTransaction.commit();
       }
   }
}
package com.example.fragmentcommunication;

import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListAdapter;
import android.widget.ListView;
import android.widget.TextView;

import androidx.fragment.app.ListFragment;

public class MasterFragment extends ListFragment {

    public interface OnMasterSelectedListener {
        public void onItemSelected(String countryName);
    }

    private OnMasterSelectedListener mOnMasterSelectedListener = null;

    public void setOnMasterSelectedListener(OnMasterSelectedListener listener) {
        mOnMasterSelectedListener = listener;
    }

    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        String[] countries = new String[]{"China", "France",
                "Germany", "India", "Russia", "United Kingdom",
                "United States"};

        ListAdapter countryAdapter = new ArrayAdapter<String>(
                getActivity(), android.R.layout.simple_list_item_1,
                countries);

        setListAdapter(countryAdapter);

        getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);

        getListView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                if (mOnMasterSelectedListener != null) {
                    mOnMasterSelectedListener.onItemSelected(((
                            TextView) view).getText().toString());
                }
            }
        });
    }
}
//layout

<?xml version="1.0" encoding="utf-8"?>
<androidx.constraintlayout.widget.ConstraintLayout 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"
    tools:context=".MainActivity">

    <FrameLayout android:id="@+id/frameLayout"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:layout_marginTop="8dp"
        app:layout_constraintBottom_toBottomOf="parent"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent" />

</androidx.constraintlayout.widget.ConstraintLayout>
<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView android:id="@+id/textViewCountryName"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />
</RelativeLayout>
//layout-land

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="horizontal">
    <FrameLayout android:id="@+id/frameLayoutMaster"
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="match_parent"/>
    <FrameLayout android:id="@+id/frameLayoutDetail"
        android:layout_width="0dp"
        android:layout_weight="1"
        android:layout_height="match_parent"/>
</LinearLayout>