package com.example.myactivityiiii;

import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.fragment.app.Fragment;

/*
* 新建一个Fragment的过程
*   1.自定义一个类，基础Fragment
*   2.配置该类的layout文件
*   3.重写onCreateView方法，加载该类的布局文件，返回一个View
* */
public class ListFragment extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(
                R.layout.fragment_list,container,false
        );
        return view;
    }
}

package com.example.myactivityiiii;

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

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

import java.util.zip.Inflater;

public class DetailFragment extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View view = inflater.inflate(
                R.layout.fragment_detail,container,false
        );
        return view;
    }
}

<fragment
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:name="com.example.myactivityiiii.ListFragment"
    android:id="@+id/list"
    android:layout_weight="1"/>

<fragment
    android:layout_width="wrap_content"
    android:layout_height="match_parent"
    android:name="com.example.myactivityiiii.DetailFragment"
    android:id="@+id/detail"
    android:layout_weight="2"/>

<?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:orientation="horizontal"
    tools:context=".MainActivity">

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Main"
        >
    </TextView>

    <FrameLayout
        android:id="@+id/frame"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        >
    </FrameLayout>

</LinearLayout>

package com.example.myactivityiiii;

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

import android.os.Bundle;

/*
* Activity运行时添加Fragment
* */
public class MainActivity extends AppCompatActivity {

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

        DetailFragment detailFragment = new DetailFragment();
        //获取Fragment的transaction实例
        FragmentTransaction ft= getSupportFragmentManager().beginTransaction();
        //指定一个容器来添加detailFragment
        ft.add(R.id.frame,detailFragment);
        //提交事物
        ft.commit();

    }
}