Fragment的两种实现方法

第一种（FrameLayout）：
布局

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.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">

    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <FrameLayout
            android:id="@+id/frag"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="9" />

        <RadioGroup
            android:id="@+id/group"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:orientation="horizontal">

            <RadioButton
                android:id="@+id/button1"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:button="@null"
                android:gravity="center"
                android:text="button" />

            <RadioButton
                android:id="@+id/button2"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:button="@null"
                android:gravity="center"
                android:text="button" />
        </RadioGroup>
    </LinearLayout>
</android.support.constraint.ConstraintLayout>

Mainactivity

public class MainActivity extends FragmentActivity {

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    
	// 2 动态加载Fragment
	// 获取fragment管理者
    final FragmentManager manager = getSupportFragmentManager();
    
    // 开启事务
    final FragmentTransaction transaction = manager.beginTransaction();
    final Frag01 frag01 = new Frag01();
    final Frag02 frag02 = new Frag02();
    
    // 把fragment对象加到事务中
	// 参数（1，帧布局的id，2.fragment对象）
    transaction.add(R.id.frag,frag01);
    transaction.add(R.id.frag,frag02);
   
    // 显示和隐藏
    transaction.show(frag01).hide(frag02);    
	// 提交(提交后事务就失效了，如果想再用就重新创建事务)
    transaction.commit();
	
	// 找到radioGroup1
    RadioGroup group = findViewById(R.id.group);
    // 设置第一个单选框选中
    group.check(group.getChildAt(0).getId());
    
    // 选中状态改变
    group.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            FragmentTransaction transaction1 = manager.beginTransaction();
            switch (checkedId){
                case R.id.button1:
                    transaction1.show(frag01).hide(frag02);
                    break;
                case R.id.button2:
                    transaction1.show(frag02).hide(frag01);
                    break;
            }
            transaction1.commit();
        }
    });
}}

第二种（Fragment And ViewPager）:
布局

  	  <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical">

        <android.support.v4.view.ViewPager
            android:id="@+id/pager"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="9" />

        <View
            android:layout_width="match_parent"
            android:layout_height="1dp"
            android:background="#000" />

        <RadioGroup
            android:id="@+id/group"
            android:layout_width="match_parent"
            android:layout_height="0dp"
            android:layout_weight="1"
            android:orientation="horizontal">

            <RadioButton
                android:id="@+id/button1"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:button="@null"
                android:gravity="center"
                android:text="首页" />

            <RadioButton
                android:id="@+id/button2"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:button="@null"
                android:gravity="center"
                android:text="站点" />

            <RadioButton
                android:id="@+id/button3"
                android:layout_width="0dp"
                android:layout_height="match_parent"
                android:layout_weight="1"
                android:button="@null"
                android:gravity="center"
                android:text="主题" />
        </RadioGroup>
    </LinearLayout>

Mainavtivity:

public class MainActivity extends FragmentActivity {

private ViewPager pager;
private RadioGroup group;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
           //找控件
	        pager = findViewById(R.id.pager);
	        group = findViewById(R.id.group);
	        
	        //默认选中
	        group.check(group.getChildAt(0).getId());
	     
	        //添加fragment集合
	        final ArrayList<Fragment> list = new ArrayList<>();
	        list.add(new Frag01());
	        list.add(new Frag02());
	        list.add(new Frag03());
   		
   		//适配器
        pager.setAdapter(new FragmentPagerAdapter(getSupportFragmentManager()) {
            @Override
            public Fragment getItem(int i) {
                return list.get(i);
            }	
            @Override
            public int getCount() {
                return list.size();
            }
        });
        
		//页面切换
        pager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int i, float v, int i1) {	
            }
        @Override
        public void onPageSelected(int i) {
            group.check(group.getChildAt(i).getId());
        }
        @Override
        public void onPageScrollStateChanged(int i) {
        }
    });
    
    //按钮点击
    group.setOnCheckedChangeListener(new RadioGroup.OnCheckedChangeListener() {
        @Override
        public void onCheckedChanged(RadioGroup group, int checkedId) {
            switch (checkedId){
                case R.id.button1:
                    pager.setCurrentItem(0);
                    break;
                case R.id.button2:
                    pager.setCurrentItem(1);
                    break;
                case R.id.button3:
                    pager.setCurrentItem(2);
                    break;
            }
        }
    });

}}