ViewPager嵌套ViewPager

ViewPager嵌套ViewPager的实现可以通过使用Fragment来实现。具体步骤如下：

1. 创建外层ViewPager的适配器，内层ViewPager的适配器和内层ViewPager的Fragment适配器；
2. 在外层ViewPager的Fragment中创建内层ViewPager，并设置内层ViewPager的适配器为内层ViewPager的适配器；
3. 在内层ViewPager的Fragment中创建需要的子Fragment，并设置内层ViewPager的Fragment适配器为子Fragment的适配器。

代码示例：

public class OuterFragment extends Fragment {

    private ViewPager mInnerViewPager;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_outer, container, false);
        mInnerViewPager = view.findViewById(R.id.inner_view_pager);

        InnerPagerAdapter innerPagerAdapter = new InnerPagerAdapter(getChildFragmentManager());
        mInnerViewPager.setAdapter(innerPagerAdapter);

        return view;
    }

    private class InnerPagerAdapter extends FragmentPagerAdapter {

        public InnerPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            return InnerFragment.newInstance(position);
        }

        @Override
        public int getCount() {
            return 3;
        }
    }
}

public class InnerFragment extends Fragment {

    private ViewPager mSubViewPager;

    public static InnerFragment newInstance(int position) {
        InnerFragment fragment = new InnerFragment();
        Bundle args = new Bundle();
        args.putInt("position", position);
        fragment.setArguments(args);
        return fragment;
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View view = inflater.inflate(R.layout.fragment_inner, container, false);
        mSubViewPager = view.findViewById(R.id.sub_view_pager);

        SubPagerAdapter subPagerAdapter = new SubPagerAdapter(getChildFragmentManager());
        mSubViewPager.setAdapter(subPagerAdapter);

        return view;
    }

    private class SubPagerAdapter extends FragmentPagerAdapter {

        public SubPagerAdapter(FragmentManager fm) {
            super(fm);
        }

        @Override
        public Fragment getItem(int position) {
            return SubFragment.newInstance(position);
        }

        @Override
        public int getCount() {
            return 3;
        }
    }
}

public class SubFragment extends Fragment {

    public static SubFragment newInstance(int position) {
        SubFragment fragment = new SubFragment();
        Bundle args = new Bundle();
        args.putInt("position", position);
        fragment.setArguments(args);
        return fragment;
    }

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

其中，fragment_outer.xml、fragment_inner.xml和fragment_sub.xml分别对应外层ViewPager的Fragment、内层ViewPager的Fragment和内层ViewPager的子Fragment的布局文件。