AS中級 フラグメント編①問題＆解説～Fragmentで１画面に２つの画面を入れる～できるけどダメな例

Fragmentで１画面に２つの画面を入れる際、できるけどダメな例を提示します。

activity_main.xmlや、fragment_top.xml、fragment_bottomは同じです。

ただし、本当にだめなのでしょうか?

なぜダメなのでしょうか?

MainActivity.java

package com.example.fragmentdemo;

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

import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

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

        TopFragment topFragment = new TopFragment();
        BottomFragment bottomFragment = new BottomFragment();

        //ここを修正
        FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();
        transaction.add(R.id.container1,topFragment);
        transaction.add(R.id.container2,bottomFragment);
        transaction.commit();
    }
}

TopFragment.java

package com.example.fragmentdemo;

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

import androidx.annotation.ColorInt;
import androidx.fragment.app.Fragment;

public class TopFragment extends Fragment {

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

BottomFragment.java

package com.example.fragmentdemo;

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

import androidx.annotation.ColorInt;
import androidx.fragment.app.Fragment;

public class BottomFragment extends Fragment {

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