FragmentPagerAdaper 实现页面切换 和 FragmentStatePagerAdapter 实现页面切换，区别，优缺点，实际开发使用哪种

1. Fragment 继承 v4 包
2. MyFragmentViewPagerAdapter 这个适配器并没有实现页面销毁方法，因此，页面较大，较多，内存压力会比较大
3. 实际开发推荐使用 FragmentStatePagerAdapter 此适配器

示例效果：

FragmentPagerAdaper 实现页面切换

Fragment1.java (除此之外还有3个一样的)

public class Fragment1 extends Fragment {
    @Nullable
    @Override
    public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {

        return inflater.inflate(R.layout.fragment_layout1,container,false);
    }
}

fragment_layout1.xml(除此之外还有3个一样的)

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <TextView
        android:text="Fragment1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
</LinearLayout>

activity_main.xml

<?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="vertical"
    tools:context=".MainActivity">

 <android.support.v4.view.ViewPager
     android:id="@+id/viewPager"
     android:layout_width="match_parent"
     android:layout_height="match_parent">

     <android.support.v4.view.PagerTabStrip
         android:id="@+id/pagerTabStrip"
         android:layout_width="match_parent"
         android:layout_height="wrap_content"></android.support.v4.view.PagerTabStrip>
 </android.support.v4.view.ViewPager>
</LinearLayout>

MyFragmentViewPagerAdapter.java

public class MyFragmentViewPagerAdapter extends FragmentPagerAdapter {
    private List<Fragment> datas;
    private List<String> titles;


    public MyFragmentViewPagerAdapter(FragmentManager fm, List<Fragment> datas, List<String> titles) {
        super(fm);
        this.datas = datas;
        this.titles = titles;
    }

    @Override
    public Fragment getItem(int i) {
        return datas.get(i);
    }

    @Override
    public int getCount() {
        return datas.size();
    }

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        return titles.get(position);
    }

    // 移除视图 未实现
}

MainActivity.java

public class MainActivity extends AppCompatActivity {

    private ViewPager viewPager;

    private List<Fragment> datas;
    private List<String> titles;
    private MyFragmentViewPagerAdapter myFragmentViewPagerAdapter;

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

        viewPager = findViewById(R.id.viewPager);

        init();
        myFragmentViewPagerAdapter = new MyFragmentViewPagerAdapter(getSupportFragmentManager(),datas
        ,titles);
        viewPager.setAdapter(myFragmentViewPagerAdapter);
    }

    private void init() {
        datas = new ArrayList<>();
        titles = new ArrayList<>();
        for (int i = 0; i < 3; i++) {
            titles.add("标题："+i);
        }
        datas.add(new Fragment1());
        datas.add(new Fragment2());
        datas.add(new Fragment3());
        datas.add(new Fragment1());
        titles.add("标题："+3);
    }
}

FragmentStatePagerAdapter 实现页面切换

MyFragmentViewPagerAdapter 稍作更改

public class MyFragmentViewPagerAdapter extends FragmentStatePagerAdapter {
    private List<Fragment> datas;
    private List<String> titles;


    public MyFragmentViewPagerAdapter(FragmentManager fm, List<Fragment> datas, List<String> titles) {
        super(fm);
        this.datas = datas;
        this.titles = titles;
    }

    @Override
    public Fragment getItem(int i) {
        return datas.get(i);
    }

    @Override
    public int getCount() {
        return datas.size();
    }

    @Nullable
    @Override
    public CharSequence getPageTitle(int position) {
        return titles.get(position);
    }

    // 相比较对 FragmentPagerAdaper 多添加下面两个方法
    @NonNull
    @Override
    public Object instantiateItem(@NonNull ViewGroup container, int position) {
        return super.instantiateItem(container, position);
    }

    @Override
    public void destroyItem(@NonNull ViewGroup container, int position, @NonNull Object object) {
        super.destroyItem(container, position, object);
    }
}

MainActivity.java 添加监听器

public class MainActivity extends AppCompatActivity implements ViewPager.OnPageChangeListener {

    private ViewPager viewPager;

    private List<Fragment> datas;
    private List<String> titles;
    private MyFragmentViewPagerAdapter myFragmentViewPagerAdapter;
    private String TAG = "MainActivity";

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

        viewPager = findViewById(R.id.viewPager);

        init();
        myFragmentViewPagerAdapter = new MyFragmentViewPagerAdapter(getSupportFragmentManager(), datas
                , titles);
        viewPager.setAdapter(myFragmentViewPagerAdapter);
        viewPager.addOnPageChangeListener(this);
    }

    private void init() {
        datas = new ArrayList<>();
        titles = new ArrayList<>();
        for (int i = 0; i < 3; i++) {
            titles.add("标题：" + i);
        }

        datas.add(new Fragment1());
        datas.add(new Fragment2());
        datas.add(new Fragment3());


        datas.add(new Fragment1());
        titles.add("标题：" + 3);


    }


    // 实现以下 3 个方法
    @Override
    public void onPageScrolled(int i, float v, int i1) {
        Log.d(TAG, "onPageScrolled(int i, float v, int i1)");
    }

    @Override
    public void onPageSelected(int i) {
        Log.d(TAG, "onPageSelected(int i)");
    }

    @Override
    public void onPageScrollStateChanged(int i) {
        Log.d(TAG, "onPageScrollStateChanged(int i)");
    }
}