【ANDROID STUDIO】 Runtime Fragment

package com.example.runtimefragment;

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

import androidx.fragment.app.Fragment;

public class FragmentOne extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_one,
                container, false);
    }
}

package com.example.runtimefragment;

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

import androidx.fragment.app.Fragment;

public class FragmentTwo extends Fragment {
    @Override
    public View onCreateView(LayoutInflater inflater,
                             ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_two,
                container, false);
    }
}

package com.example.runtimefragment;

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

import android.os.Bundle;
import android.view.View;

public class MainActivity extends AppCompatActivity {

    FragmentOne mFragmentOne;
    FragmentTwo mFragmentTwo;
    int showingFragment=0;

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

        mFragmentOne = new FragmentOne();
        mFragmentTwo = new FragmentTwo();
        getSupportFragmentManager().beginTransaction().add(R.id.frameLayout, mFragmentOne).commit();
        showingFragment = 1;
    }

    public void switchFragment(View view) {
        FragmentManager fragmentManager = getSupportFragmentManager();
        FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
        if (showingFragment == 1) {
            fragmentTransaction.replace(R.id.frameLayout, mFragmentTwo);
            showingFragment = 2;
        } else {
            fragmentTransaction.replace(R.id.frameLayout, mFragmentOne);
            showingFragment = 1;
        }
        fragmentTransaction.commit();
    }
}

<?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">
    <FrameLayout android:id="@+id/frameLayout"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_above="@+id/buttonSwitch"
        android:layout_alignParentTop="true">
    </FrameLayout>
    <Button android:id="@+id/buttonSwitch"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Switch"
        android:layout_alignParentBottom="true"
        android:layout_centerInParent="true"
        android:onClick="switchFragment"/>
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent">
    <TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Fragment One"
        android:id="@+id/textView"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />
</RelativeLayout>
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_height="match_parent"
    android:layout_width="match_parent">
    <TextView android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Fragment Two"
        android:id="@+id/textView"
        android:layout_centerVertical="true"
        android:layout_centerHorizontal="true" />
</RelativeLayout>